PBG 301 Principles and Methods of Plant Breeding PDF

PBG 301 Principles and Methods of Plant Breeding 2+1 Theory (2017 Lec 1: Objectives and role of plant breeding - historical perspective – activities in Plant Breeding Plant breeding is defined as a sci...

PBG 301 Principles and Methods of Plant Breeding 2+1 Theory (2017 Lec 1: Objectives and role of plant breeding - historical perspective – activities in Plant Breeding Plant breeding is defined as a science as well as an art of improving the genetic makeup of plants in relation to their economic use. Plant breeding can be accomplished through many different techniques ranging from simply selecting plants with desirable characteristics for propagation, to more complex molecular techniques. Plant breeding has been practiced for thousands of years, since near the beginning of human civilization. It is now practiced worldwide by individuals such as gardeners and farmers, or by professional plant breeders employed by organizations such as government institutions, universities, crop-specific industry associations or research centers. Simmonds (1979) defined that plant breeding is considered as a current phase of crop evolution. International development agencies believe that breeding new crops is important for ensuring food security by developing new varieties that are higher-yielding, resistant to pests and diseases, drought-resistant or regionally adapted to different environments and growing conditions. The plant breeding field can be divided in to three important areas. 1. Plant genetic resources (or) germplasm 2. Breeding techniques 3. Seed production techniques 1.Germplasm: It is the total variability found in plant species. It deals with collection, conservation, evaluation, documentation and utilization of cultivated and wild relatives of crop plants. 2. Breeding techniques: Deals with various genetic principles and procedures of crop improvement. 1. General breeding methods: This includes introduction, selection, and hybridization (inter varietal hybridization) 2. Special breeding techniques: Mutation breeding, polyploidy, wide hybridization and other special techniques like tissue culture and genetic engineering in crop improvement.  3. Seed production techniques: Deals with principles and methods of seed production. Objectives of plant breeding: The main objective of plant breeding is to develop superior plants over the existing ones in relation to their economic use. Thus, crop improvement with improved agronomic characters and resistance against biotic and abiotic stresses are the main objective and common objective of any breeding programme. A brief account of some important objectives are given below 1. Increased yield Majority of our breeding programmes aims at increased yield. This is achieved by developing more efficient genotypes. The classical examples are utilization of Dee Gee Woo Gen in rice and Norin10 in wheat. Identification and utilization of male sterile lines for hybrid variety development. 2. Improving the quality – it differ from crop to crop Rice -milling, cooking quality, aroma and grain colour Wheat- milling and baking quality and gluten content. Barley – malting quality pulses -Protein content and improving sulphur containing amino acids oilseeds- PUFA (Polyunsaturated fat) content 3. Elimination of toxic substance HCN content in jowar plants Lathyrogen content in Lathyrus sativus ( β-N-oxalyl-amino-L-alanine- BOAA) Erucic acid in Brassicas Cucurbitacin in cucurbits Gossypol in cotton 4. Resistance against biotic and abiotic stresses Biotic stress: Evolving pests and diseases resistant varieties there by reducing cost of cultivation, environmental pollution and saving beneficial insects. Abiotic stress: It is location specific problem. Soil factors and edaphic factors sometimes poses severe problems. Breeding resistant varieties is the easy way to combat abiotic stress. 5. Agronomic characteristics – modification of agronomic characters such as plant height, tillering, branching, erect or trailing habit etc., is often desirable. In cereals dwarfness highly associated with lodging resistant and fertilizer responsiveness. – E.g. Rice, Bajra 6. Photo and thermo- insensitivity: Photo and thermo – insensitive wheat and photo insensitive rice has permitted their cultivation in new areas. Eg. Redgram, sorghum. 7. Synchronized maturity – one time harvest eg. Pulses 9. Non-shattering nature – Avoid wastage during harvesting due to over maturity eg. Green gram, Brassicas 11. Determinate Growth habit – determinate growth – Pulses 12. Elimination or introduction of dormancy – Groundnut Roll of plant breeding Since the cultivable land is shrinking and there is no scope for increasing the area under cultivation, the only solution to meet the food requirement is by increasing the crop yield through genetic improvement of crop plants. There are two ways by which yield improvement is possible. 1. Enhancing the productivity of crops This can be done a) By the proper management of soil and crops involving suitable agronomic practices and harvesting physical resources. b) By using high potential crop varieties created by appropriate genetic manipulation of crop plants. 2. Stabilizing the productivity achieved This is done by using crop varieties that are bred especially for wide adaptation or for specific crop zones to offset the ill effects of unfavorable environmental conditions prevailing in the areas. Plant breeding, the past, present and future scopes Indian agriculture remained stagnant particularly during early sixties. Long spells of severe drought and serious outbreak of disease in some parts of the country led some futurologists to state that a possible doom in India by the end of the decade. However, we achieved breakthrough in crops such as rice, wheat, pearlmillet, jowar and maize. 1. The indica x japonica cross derivative ADT 27 is the first high yielding rice of Tamil Nadu. The identification of Dee Gee Woo Gen and release of Wonder rice IR 8 (Peta x DGWG) changed the scenario from poverty to problem of plenty. 2. Like wide identification of dwarfing gene in Japanese wheat variety Norin-10 by Borlaug and breeding of Mexican dwarf wheat varieties led to the release of wheat varieties life Kalyan sona in India.  3. In pearl millet, breeding by male sterile line Tift 23A at Tifton, Georgia by Burton and his coworker and later on its introduction to India led the release of hybrid bajra HB1 to HB4, which increased bajra production many fold. In Jowar, breeding of first male sterile line combined kafir 60A and its introduction into India led to the release of first hybrid sorghum CSH 1 (CK 60A x IS 84) during 1970s. 4. At present we are in search of alternate source of cytoplasm in almost all crops to breed hybrids with new source of cytoplasm to prevent the possibility of appearance of new pest and diseases. Thus, the future of plant breeding is a challenging task. The deployment of innovative breeding techniques will be a new tool to assist the conventional breeding techniques. Undesirable consequences of Plant Breeding 1. Genetic erosion: Disappearance of land races due to introduction of high yielding varieties. Eg. Introduction of IR 20 rice led to disappearance of land races of samba rice. 2. Narrow genetic base: Genetic vulnerability to pest and diseases. Tift 23A - Bajra - Susceptible downy mildew, T cytoplasm - Maize - susceptible to Helminthosporium 3. Minor disease and pest become major due to intensive resistance breeding RTV (Rice Tungro Virus) Grey mold in Bengalgram 4. Attainment of yield plateau: No more further increase in yield. History of Plant Breeding It started when man first chose certain plants for cultivation. There is no recorded history when the plant breeding started. As early as 700 BC Babylonians and Assyrians artificially pollinated the date palm. In 1717 Thomas Fairchild produced the first artificial hybrid popularly known as ‘ Fairchild mule’ by crossing carnation with sweet William. Joseph Koelreuter, German made extensive crosses in Tobacco between1760 - 1766 and emphasized hybrid vigour in F1. Thomas Andrew Knight (1759-1835) was the first man to produce several new fruit varieties by using artificial hybridization. Le Couteur, a farmer of the Isle of Jersey published his results on selection in wheat in the year 1843. He concluded that progenies from single plants were more uniform than the remaining population. Patrick Shireff a Scotsman practiced individual plant selection in wheat and oats and developed some valuable varieties.  Loui de -Vilmorin (1856) proposed the Vilmorin principle of Vilmorin isolation principle which is basic for progeny test. Nilsson-Ehle and his associates in Swedish Seed Association, Svalof Sweden (1890) refined the single plant selection. In 1903 Johannsen the famous ‘ pure line theory’ provided the genetic basis for individual plant selection. Which states that a pure line is progeny of a single self fertilized homozygous plant. He proposed this theory based on his studies in Phaseolus vulgaris. 1908 East and G.H. Shull studied the inbreeding in maize paved the way for the development of hybrids in maize and later several other crops. 1927 – Muller explained mutagenic action of X rays 1928 - Stadler produced mutations in barley First mutation breeding programme launched in 1929 in Sweden by Ake Gustafsson and co-workers. 1928 Inter specific cross by Karpechenko (Radish x Potato) 1937 doubling action of colchicine discovered independently by Blakeslee and Nebel. During 1960’ s Norman Borlaug and his associates developed Mexican semi dwarf wheat varieties, which paved the way for green revolution in wheat. The dwarfing gene was isolated from Japanese wheat variety Norin 10. Later on this Mexican dwarf were introduced in the India by Dr. M.S.Swaminathan and a number of high yielding wheat varieties like Kalyan Sona, Sonalika were developed. In rice the identification of dwarf gene Dee Geo Woo Gen from a dwarf , early maturing variety of japonica rice from Taiwan. By using this gene Taichung Native 1 (TN1) was developed in Taiwan and IR 8 developed at IRRI Philippines were introduced in India in 1966. Somatic hybridization -1972 -Carlson and co-workers – fusing the protoplasts of Nicotiana glauca x N. langsdorffii Nobilisation in sugarcane by C.A. Barber and T.S.Venkataraman is another monumental work in plant breeding. 1996 – Genetically modified insect resistant varieties of cotton, maize and soyabean commercially cultivated in U.S.A. History of Plant Breeding in India  Organized agricultural research in India dates back to 1871, when the government of India created the Department of Agriculture. The first scientist to be appointed in the department (in 1892) was an agricultural chemist. In 1905, the Imperial Agricultural Research Institute was established in Pusa, now in Bihar, this was the first agricultural research institute in the country. The buildings of this institute were damaged by an earthquake in 1934; the institute was, therefore, shifted to its present location in New Delhi in 1936. The name of the institute was changed to its present one. i. e. Indian Agricultural Research Institute, in the year 1946. Agricultural colleges were established at Kanpur, Pune, Sabour, Llyalpur and Coimbatore between the years 1901 and 1905. o The main objective of these colleges was to impart agricultural education and training. About this time, a number of Agricultural Research Farms were established in each province. But the progress in Agricultural research was disappointingly slow. o In view of this, the Imperial Council of Agricultural Research was established in 1929, its name was changed to the present Indian Council of Agricultural Research (ICAR) in 1946. The Indian Central Cotton Committee was established in 1921. The committee carried out many notable researches on breeding and cultivation of cotton, E. g Development of 70 improved varieties of cotton. Encouraged by these results, central commodity committees were set up on jute, sugarcane, tobacco, oilseed, coconut, arecanut, spices , cashewnut and lac. ( a total of 9 committees). Subsequently, these committees were merged in the ICAR. In 1956, a project for Intensification of Regional Research on Cotton, Oilseed and Millets (PIRRCOM) was initiated in order to intensify research on these crops. The PIRRCOM was located at 17 different centres spread throughout the country; it focused on cotton, castor, and groundnut, Brassica sp, Gingelly (Til), torai, taramira, jowar, and bajara. The all Indian Coordinated Maize Improvement Project was started in 1957, with the objective of exploiting heterosis. The first hybrid maize varieties developed under the project were released in 1961. The phenomenal success of this project prompted the ICAR to initiate coordinated project, for the improvement of other crops as well. The ICAR was reorganised twice in 1966 and 1973 with a view to improve its efficiency. The first agriculture university was established in 1960 at Pantnagar, Nainital (U.P). Subsequently, such universities were established in most other states of the country.  In some states, E. g U.P and Maharashtra, there are 4 universities each. The agriculture university have the responsibility for education, research and extension in the different areas of agriculture. In addition, over two dozen different Central Research Institute of ICAR are engaged in crop improvement activities. Activities in Plant Breeding The desired changes in genotypes of crop species and the consequent benefits to farmers are brought about by a series of interrelated and largely interdependent activities, namely, 1) Creation of variation – Genetic variation is a pre request for any genetic improvement in a crop. Hence in any plant breeding programme, this is the first step unless genetic variation pre-exists in the breeding programme. This can be created by domestication, germplasm collection, plant introduction, hybridization (intervarieteal, distant, somatic), mutation, polyploidy, somaclonal variation and genetic engineering. 2) Selection - The next step consists of identification and isolation of plants having the desirable combination of characters, and growing their progeny; this is called Selection. Selection is ordinarily based on phenotype, but marker-assisted selection is based on genotype of the concerned trait(s). The efficiency of selection determines the success of a breeding program. Various breeding methods have been designed to increase the efficacy of selection. Selection finally yields improved lines strains or populations that must be evaluated for their performance. 3) Evaluation – Newly selected lines/strains/populations are evaluated for yield and other traits and their performance is compared with the existing best varieties called checks. Evaluation is a stepwise process; in India, it is ordinarily conducted at several locations for three or more years under the concerned All India Coordinated Crop Improvement project. IF the new line/strain performed superior than checks, it is released as a new variety; the seeds can now be multiplied and more importantly certified for quality. 4) Multiplication - It large scale production of quality seed of the released and notified variety. Seed production is usually done by seed production agencies in a step-wise manner, and the seed is certified by a seed certification agency 5) Distribution – Certified seed is ultimately sold to the farmers who use it for commercial crop cultivation. This activity alone makes it possible to reap the economic benefits from the above activities in the form of (1) enhanced and (2) stable production of (3) superior produce (4) often at lower costs. Lec 2 : Centres of origin – contribution of Vavilov, Harlan, Zhukovosky – law of homologous series The cultivation of plants is one of man’ s oldest occupations and probably began when he selected some plants for his use. One of the old belief regarding to the origin of cultivated plants was that they came to man as a gift from God. By the end of 18th century people started questioning about the origin of cultivated plants. Darwin (1868) considered that the cultivated plants arose by profound modifications in the wild plant. Alphonse de Candolle (1863) a Swiss botanist first attempted to solve the mystery about evolution of crop plants. In his “ Origin of cultivated plants” he studied 247 plant species of cultivated plants. He classified the economic plants into six classes; 1. Plants cultivated 4000 years ago. 2. Plants cultivated 2000 years ago. 3. Plants cultivated less than 4000 years. 4. Plants cultivated 2000 to 4000 years. 5. Plants cultivated before the time of Columbus. 6. Plants cultivated after the time of Columbus. It is N.I.Vavilov who proposed the concept of ‘ centres of origin’. He proposed the concept based on his studies of a vast collection of plants at Institute of Plant Industry, Leningrad. The concept is that crop plants evolved from wild species in the area showing great diversity and that place is termed as primary centre of origin. Later on from the primary centre the crops moved to other places due to the activities of man. There are certain areas where some crops exhibit maximum diversity of forms but this may not be the centre of origin for that particular crop. Such centres are known as Secondary centres of origin. E.g. cow pea (China) The primary centre of origin for this crop is Africa but India exhibits maximum diversity for this crop. Vavilov centers are regions where a high diversity of crop wild relatives can be found, representing the natural relatives of domesticated crop plants. Nikolai Vavilov initially identified 8, later in 1935 Vavilov divided the centers into 12, giving the following list: 1. Chinese center 2. Indian(Hindustan) center  3. Indo-Malayan center 4. Central Asiatic center 5. Persian center 6. Mediterranean center 7. Abyssinia center 8. South American center 9. Central American center 10. Chilean center 11. Brazilian center 12. US center Vavilov originally proposed Eight main centres of origin. Eight main centres of origin are recognised by Vavilov, they are: 1.China 2.Hindustan 3.Central Asia 4.Asia minor 5.Mediterranian 6.Abyssinya 7.Central America 8.South America 1. The China centre: It consists of the mountainous regions of central and western China and the neighbouring low lands. It is the largest and oldest independent centre. The crops originated in this centre are: I.Primary centre of origin are: ii. Secondary centre of origin are: Soybeans Maize Radish Cowpea Proso millet Turnip Opium Sesame Brassica Onion 2.The Hindustan Centre: This includes Burma, Assam, Malaya, Java Borneo, Sumatra and Philippines, but excludes North West India, Punjab and North Western Frontier Provinces. The crops originated in this centre are: i. Primary centre of origin are: ii. Secondary centre of origin are: Rice Cucumber Redgram Radish Chickpea Noble canes Cowpea Cotton (Gossypium arboreum) Greengram Hemp Turmeric Coconut 3.The Central Asia Centre: It includes North West India, all of Afghanistan, the Soviet Republics of Tadjikistan and Tian Shan. It is also known as the Afghanistan centre of origin. The crops originated in this centre are: i. Primary centre of origin are: ii. Secondary centre of origin are: Wheat Rye Pea Broad bean Green gram Sesame Safflower Cotton(G.herbaceum) Onion Garlic 4.The Asia Minor Centre: This is also known as the Near East or the Persian Centre of Origin. It includes the interior of Asia Minor, the whole of Transcaucasia, Iran and Highlands of Turkmenistan. The crops originated in this centre are: i. Primary centre of origin are: ii. Secondary centre of origin are: Triticum Rape Rye Black Mustard Alfalfa Turnip Cabbage Oats 5.The Mediterranean Centre: The crops originated in this centre are: i. Primary centre of origin are: Many valuable cereals and legumes such as; Durum Wheat Chikpea Emmer Wheat Beets  Barley Peppermint Lentil Pea Broad bean 6.The Abyssinian Centre: It includes Ethiopia and hill country of Eritrea. The crops originated in this centre are: i. Primary centre of origin are: ii. Secondary centre of origin are: Barley Broad bean Sorghum Pearl millet Lentil Khesari Sunflower Castor Coffee Okra 7.Central American Centre: This includes South Mexico and Central America.It is also referred to as the Mexican Centre of Origin. The crops originated in this centre are: i. Primary centre of origin are: Maize Lima bean Melons Pumpkin Sweet Potato Arrowroot Cotton (G.hirsutum) 8. The South American Centre: This centre includes the high mountainous regions of Peru, Bolivia, Ecuador, Colombia, parts of Chile, and Brazil and whole of Peraguay The crops originated in this centre are: i. Primary centre of origin are: Potato Maize Lima bean Peanut  Egyptian cotton (G.barbadense) Tobacco Tapioca Later in, 1935, Vavilov divided the Hindustan Centre of Origin into two centres, viz., Indo Burma and Siam- Malaya-- Java Centre of Origin. The South American Centre was divided into three centres, namely, Peru, Chile and Brazil-Peraguay Centres of Origin. At the same time he introduced a new centre of origin, the U.S.A. Centre of origin. Two plant species, Sunflower(Helianthus annuus) and Jerusalem Artichoke (H.tuberosus) originated in the U.S.A. Centre of origin. Thus the centres of origin may be more appropriately called the centres of diversity. The centres of diversity may not be the centres of origin of the species concerned, but they are the areas of maximum diversity of the species. Within the large centres of diversity, small areas may exhibit much greater diversity than the centre as a whole. These areas are known as Microcentres. OBJECTIONS TO VAVILOV’ S THEORY According to Vavilov whenever a crop plant exhibits maximum diversity, that place is the centre of origin for that crop. But this view is no longer valid. E.g. maize and tomato. For maize the centre of diversity is Peru but archeological evidence shows Mexico as centre of origin. For tomato, South America is considered to be primary centre of origin but it is Mexico as per archeological evidence. Secondly Vavilov stated that primary centre is marked by a high frequency of dominant genes in the centre and recessive genes towards the periphery. But it is not so. E.g. Wheat, maize, oil palm Vavilov’ s claim that centre of origin confined to mountainous regions only. But this is not the case. For E.g. Maize exhibits maximum diversity in plains Many crops have more than one centre of origin E.g. Balsam, Sorghum. In some crops centre of domestication cannot be determined for want of suitable evidence. `To counter the objection, Zhukovsky student of vavilov has proposed ‘ mega centre’ theory. He divided the world into 12 regions. Mega gene centres were the places where cultivated plant species exhibit diversity and micro gene centre is the place where wild species occur. Harlan stated that each crop may have been repeatedly domesticated at different times in different locations or may have been brought into cultivation in several regions simultaneously. We cannot pin point a single centre of origin. Harlan developed the idea of ‘ Centre’ and ‘ Non- centre’. According to him ‘ centre’ means places of agricultural origin and ‘ non centre’ where agriculture has been introduced. Harlan divided the world in to three centres and three non centres. LAW OF HOMOLOGOUS SERIES: This is proposed by N.I Vavilov. According to this law “ the characters found in one species also observed in other related species”. Thus diploid, tetraploid and hexaploid wheats show a series of identical characters. So also in case of diploid and tetraploid cotton. Similarly genus Secale duplicates the variation found in Triticum. Harlan's most recent theory (1992) Certain biomes or vegetation types may have been more conducive to domestication than others. A biome is a major regional terrestrial community with its own type of climate, vegetation and animal life. Biomes are not sharply separated, but merge gradually into one another over what is called an ecotone Plant Genetic Diversity Variety of genes and genotypes found in a crop species. Genetic diversity – broad genetic base to population. N.I. Vailov (1926, 1951) realized the importance. Proposed eight main centers of diversity and three subsidiary centers. Vavilov not covered Africa, Australia. Primary Centres of Diversity. - Regions of vast genetic diversity - Large number of dominant genes - Mostly have wild characters - Less crossing over - Natural selection operates. Secondary centers. - lesser genetic diversity - large number of recessive genes - have desirable characters - more crossing over - both natural and artificial selections operate. Microcenters  - Small areas – tremendous genetic diversity. - Study of evolution of cultivated species. Vavilov – parallel series of variation – Law of homologous series of variation. Particular variation in a crop another related spread Lec 3: Plant genetic resources – importance – germplasm – types – activities – gene erosion - gene bank – collection - conservation – types of conservation – Plant genetic resources. Plant genetic resources (PGR) are the basic materials that are essential for development of improved crop varieties designed to combine high yield potential with superior quality, resistance to diseases and pests, and also better adaptation to abiotic stress environments. Their continued availability to plant breeders is necessary not only for sustaining advances in crop productivity but also for stabilising production in the country. These resources of known or potential use to man constitute a broad spectrum of diverse gene pools representing assemblage of landraces, primitive cultivars, varieties of traditional agriculture as well as wild and weedy relatives of crop plants. In the last two decades or so, much attention has been drawn to indigenous locally adapted cultivars in particular because of the useful genetic variation they contain as an invaluable resource for present and future plant breeding, and the rapid rate at which they are disappearing through replacement by high yielding varieties. In addition, the natural habitats of wild relatives of crop plants are continuously getting eroded threatening survival of these populations. This diversity is not yet adequately represented in the existing collections at national, regional and international levels. Indian national programme on genetic conservation aims at exploring and collecting, classifying, evaluating, conserving and documenting this natural heritage for its current and future use. All these operations constitute a chain of activities that are now better understood and carried out by the national and international centres mandated with such responsibilities. The last thirty years have seen the great upsurge of this activity, with more awareness generated by the FAO, Biodiversity International (IPGRI), and the IARCs and also by the IUCN, UNESCO and the WWF in their concern for conservation of biodiversity with particular reference to in-situ aspects. Equally important in this context has been the phenomenal growth in biotechnology during the past two decades which has also created new awareness about the value of plant genetic resources since sexual process of fertilisation and recombination was no longer a pre-requisite to shuffling of desirable traits.  A broad outline of plant genetic resources' activities has already been presented in the first chapter as an introductory part. In the following chapter, importance of geographical areas of diversity of crop plants and the richness of this genetic wealth in the Indian subcontinent has been reflected. Subsequent chapters deal largely with the methodologies and approaches that are followed in executing PGR activities, viz. germplasm collection, introduction, exchange and quarantine, characterization and evaluation, maintenance, documentation, conservation and utilisation. In this chapter, the work carried out by the National Bureau of Plant Genetic Resources (NBPGR), the national nodal organisation for such activities, and its coordinating role in the management and monitoring of these activities has been highlighted with a view to focussing attention on the newly emerging Indian National Plant Genetic Resources System. Brief history in India Indian interest and abiding concern in the collection and utilisation of plant genetic resources dates back to the early decades of this century (Howard and Howard, 1910), though botanical accounts on available flora and the economic plants/products had been documented much earlier (Hooker, 1872-97; Watt, 1889-93). However, it was late Dr. B.P. Pal who truly focussed attention on the use of germplasm variability in crop improvement in national context. The publication of his paper, ‘The search for new genes', in fact, paved the way for augmenting genetic diversity for use in plant breeding (Pal, 1937; Pal and Singh, 1943). It was primarily due to his foresight and wisdom that a nucleus Plant Exploration and Collection Unit was established in 1946 in the Division of Botany at the Indian Agricultural Research Institute, New Delhi. This unit became a regular wing in 1956 that was raised to the status of a Division of Plant Introduction in 1961. The late Dr. Harbhajan Singh dedicated his entire services to operate and boost these activities from the beginning and particularly so during the 1960s-1970s. (Singh and Hardas, 1970; Singh, 1973). Dr. M.S. Swaminathan and Dr. A.B. Joshi further strengthened the foundations of these activities. To serve the needs of the ICAR crop research institutes, all India coordinated crop improvement projects and state agricultural universities, the Indian Council of Agricultural Research created a separate organisation named as National Bureau of Plant Genetic Resources (NBPGR) in 1976 alongwith two other Bureaus concerned with animal and fish genetic resources. PLANT GENETIC RESOURCES Sum total of genes in a crop species - ‘ Genetic resources’ or ‘ gene pool’ , ‘ genetic stock’ , ‘ germplasm’ - Whole library of different alleles of a species - Basic materials for initiation of breeding programme. Features: - Entire genetic variability - Land races, modern cultivars, obsolete cultivars, breeding stocks, wild forms, species - Cultivated & wild species - Collected from centers of diversity, gene bank, gene sanctuaries, farmers field, market and seed companies. - Basic material Classification of gene Pool 1) Area of collection 2) Domestication 3) Duration of conservation 4) Crossability in breeding program. 5) 1) Area of collection: a) Indigenous b) exotic 2) Domestication: a) Cultivated b) wild 3) Duration of conservation: a) Base collection: Base collections include maximum number of accessions available in a crop. Long term storage upto 50 years or more. Seed viability not less than 95% , Seeds with 5 + 1 % moisture content stored at -18OC to – 20OC. These collections are distributed only for the purpose of regeneration. It is also known as principle collection and refers to the whole collection. b) Active collections This category of germplasm is actively utilized in breeding programmes and are conserved for medium term (8-10 years or more). These collections are stored at zero degree cesius with moisture content around 8%. Germination test is carried out after every 5-10 years to assess the reduction in seed viability. c) Working collection: These collections are frequently utilized by breeders in their crop improvement programmes. These are stored for short term ( 3 to 5 years ). The seed is stored at 5OC – 10OC with moisture content of 8-10%. 4) Crossability in Breeding Program 1) Primary gene pool GP1: Intermating is easy – production of fertile hybrids. Same species or closely related. 2) Secondary gene pool GP2: Partial fertility on crossing with GP1 plants related species. 3) Tertiary gene pool GP3: Sterile hybrids on crossing with primary gene pool. Needs special techniques. Components of Genetic Resources Various plant materials constituting gene pool. 1) Land races: Primitive cultivars. - evolved under sub resistance agriculture - High level of genetic diversity – diseases, pests - Broad genetic base - Less uniform - Low yielders 2) Obsolete cultivars - Improved varieties of recent part - Replaced by new varieties. - Wheat varieties K68, K65, pb591 – Traditional Tall before Mexican wheat attractive grain color and good chapatti making. 3) Modern cultivars - Currently cultivated high yielding varieties. - High yield potential, uniformity, parents in breeding program Narrow genetic base - low adaptability. 4) Advanced breeding lines Pre-released plants developed by plant breeders. Not yet ready for release. 5) Wild forms of cultivated species. High degree of resistance. 6) Wild relatives. 1) Hybrid sterility problems in crossing 2) Hybrid invariability 3) Undesirable genes with desirable alleles. 7) Mutants Mutant gene pool Dee-Geo-Woo-Gen in rice and Norin 10 in wheat. Valuable genetic resources. In seed propagated crops, 410 varieties have been released. GERMPLASM The germplasm collection is a collection of large number of genotypes of a crop species and its wild relatives. In other words it is the sum total of hereditary or genes present in a species. Therefore, germplasm consists of the following five types of materials: (1) land races, (2) obsolete varieties, (3) varieties in cultivation, (4) breeding lines, and (5) wild forms and wild relatives. Germplasm collections are also known as gene banks or gene pool or world collection. The term working germplasm refers to the smaller number of collections kept by a breeder for hybridization programme. Need for Germplasm Bank : a) The modernisation of agriculture and evolution of high yielding varieties and hybrids led to the replacement of the land races. For examples after the introduction of IR 20 rice for samba season all the local varieties like karthigai samba, Toppi sampa, Rubber samba, Thiruchengodu samba. Athur samba went out of cultivation. Along with them the beneficial genes also vanished. This is known as genetic erosion or in other words narrowing down of variability. So, to prevent the loss of variability in cultivated forms and their wild relatives (Genetic erosion) it is necessary to maintain germplasm. b) Nature has provided enormous variability for the use of mankind. We should not destroy them and preserve them for the use of future mankind. Germplasm conservation : Conservation is the management, preservation and use of known genetic resources so that they may yield the greatest sustainable benefit to the present generation, which maintaining their potential to meet the needs and aspirations of generations to come (IUCN, 1980) There are two methods of conserving germplasm: in situ and ex situ (Frankel and Soule, 1981). Conservation in situ involves the setting aside of natural reserves to conserve species in natural habitats. This type is also classified as dynamic evolutionary conservation. Plants and animals are conserved in entire biomes free to evolve through natural selection. Extinction of species is deterred but this method has little impact on useful plants. Gene Sanctuaries or Insitu conservation: The areas of diversity are protected from trespass of human beings by fencing the area so that the plant species are preserved under natural conditions. This is known as insitu conservation. E.g. Meghalaya for citrus, North Eastern Region for Musa, Oryza, Saccharum. Exsitu conservation: Conservation ex situ is the conservation of species out of their natural habitat (Hoyt, 1988). There are three main methods of ex situ conservation: seed banks, field genebanks and tissue culture. Collections of germplasm using any of these methods are often called genebanks. With the advent of biotechnology a genebank may also include a. collection of cloned DNA fragments from a single genome and, ideally, representing the whole of the genome. There are two types of conservations are Short term conservation: Based on the viability of the seeds the gene pool is to grown once in two years or more than two years. Each line is to be grown with proper spacing and care must be taken to ensure self pollination, so that the genetic architecture is not altered. For example in sorghum covering the panicle in boot leaf stage it ensures selfing. This short term conservation is a costly affair which requires much time, labour, land and cost. Further there is every chance for mixing up of genotypes while large number is handled annually. Long term conservation : To overcome this difficulty long term preservation in the cold storage the germplasm can be preserved. Using liquid nitrogen the germplasm can be stored for more than ten years. Complete information about the genotypes can be computerized and this is known as cataloguing and information retrieval system. Exploratory Surveys : NBPGR will arrange for survey and collection of germplasm. Explorations generally cover those that are likely to show great diversity of forms. Tribal areas will have more forms of diversity. Along with ICRISAT, NBPGR the TNAU has conducted exploratory surveys for collection of small millets, sorghum and pearl millet. The palamalai hills of Coimbatore is a rich source of diversity for sorghum. Sorghum halapense both 2n = 20 and 2n = 40 forms are available there. The Kodaikanal hills are having S.nitidum under natural conditions. In southern districts S.stafii is available. Anaikatti hills are rich source of diversity for small millets. Normally during surveys the samples collected will be of three kinds. a) Field Sample : Seeds collected from field or farm areas where it is available. b) Market sample : Types available in local shandies or market will be collected. c) Storage sample : By visiting the houses of farmers the seeds stored for sowing will be collected. Centres maintaining germplasm 1. Institute or plant Industry, Leningrad. 2. Royal Botanic Gardens, Kew, England. 3. USDA, Beltsville. 4. ICRISAT. Sorghum, Red gram, Ground nut, Pearl millet and Bengal gram 5. IRRI - Rice 6. World vegetable centre - Taiwan - Soybean 7. Biodiversity International (IPGRI ) - International Germplasm Repository. 8. NBPGR - National Germplasm Repository. Genetic erosion : The loss of genetic material (genes, genotypes) from individuals or populations is termed genetic erosion (IBPGR, 1991). Reason for genetic erosion 1. Changing patterns of land use such as clearing of forests, housing and industrial developments contribute to genetic erosion. 2. So does changing cultural practices particularly the widespread use of a limited number of standard varieties in lieu of the genetically rich old and traditional populations of cultivated species. 3. The threat of genetic erosion is real. There are several recorded epidemics due to diminished genetic diversity resulting into increased genetic vulnerability in major crops (NAS, 1972). a. 1840 famine in Ireland due to potato late blight (Phytophthora infestans) b. 1917 wheat less days in USA due to stern rust epidemics (Puccinia gram in is) c. 1943 famine in. Bengal, India due to brown spot disease of rice (Cochliobolus miyabeanus) and d. a typhoon Mid 1940s complete elimination of all oats derived from the variety Victoria in the U.S. due to the Victoria blight disease (Helminthosporium victoriae) e. 1970-71 southern corn leaf blight (Helminthosporiuni maydis) epidemic on all U.S. corn hybrids carrying the T-type cytoplasmic male sterility f. In rice, recent epidemics associated with the widely grown and muliple-cropped semidwarfs have been pointed out (Chang, 1979, 1984). Lec 4 Germplasm: evaluation – use of descriptors, documentation, utilization; Agencies – national and international; germplasm exchange – quarantine. Germplasm activities. 1) Exploration and collection. - Collection trips tapping genetic diversity from various sources. - assembling at one place. Reduction in genetic variability a) Replacement of land races with improved cultivars b) Modernization of agriculture – eliminates wild & weedy former. c) Extension of farming into wild habits. d) Grazing into wild habitats. e) Growth of cities. ii) Extraction: Permanent loss of a crop species. Process 1) Sources of collection: Centres of diversity gene bank gene sanctuaries seed companies farmers fields 2) Priority of collection: Endangered areas, endangered species 3) Agencies of collection: SAU ICAR (Biodiversity International) IPGRI 4) Method of collection: Expeditions, personal visit to gene bank, correspondence, exchange of material. 5) Method of sampling: Random sampling – biotic tolerant stresses Biosed sampling – distinct morphological characters. 6) Sample rice: 95% of total diversity should be caps there. 50 – 100 individuals, 50 seeds/ plant. Merits 1) Tapping crop genetic diversity 2) New material, prevents extraction Demerits entry of new disease, remote areas. 2. Conservation Protection of genetic diversity of plants from genetic erosion. In situ Conservation: under natural conduction. Establishment of biosphere reserves. - Costly method, several areas have to be conserved. Ex situ conservation: Preservation of germplasm in gene banks. Cheaper, easy, entire genetic diversity conserved. Seed Meristem easy Long term (50-100 years) Medium term (10-15 years) Short term (3-5 years) Robert (1973) – Orthodox – dried to low moisture content, no loss in validity. Eg: wheat, papaya, various beans. - recalcitrant Drastic loss in viability with a decrease in meristem below 12-13OC Eg: Cocoa, margo, tea, coffee, jackfruit, ruble. Meristem Merits – free from virus - Vegetatively propagated crop. - Perennial plants - Regeneration easy 3. Evaluation: 1) to identify gene sources 2) classification of germplasm. - by simple measures of dispersion (Range, standard deviation, SE, CV) - by metroglyph analysis of Anderson (1957) - D2 statistic of Maharlanobis (1936) 4. Documentation Compilation, analysis, classification, storage, dissemination of information. Information system. - provides information about various activities of plant genetic resistance. - 7.3 million germplasm accession – 200 crop species. Biodiversity International - (IPGRI) – descriptor 5. Distribution: Specific germplasm – supplied on demand. 6) Utilization use of germplasm in crop improvement programme cultivated germplasm - as a variety - as parent - as variant in gene pool. Wild – Transfer of resistance. Biodiversity International (IPGRI) – Supervised by consultative group on international Agricultural Research (CGIAR) CGIAR – 1972 by FAO, world bank. UNDP to establish international research Institutes. Biodiversity International (IPGRI) established by CGIAR in 1994. Conducting research and to promote an International Net work of plant Genetic Resources. IBPGR Till 1993 – IBPGR 1974. NBPGR NBPGR – by ICAR – 1976 – New Delhi 1946 – plant introduction started at IARI, New Delhi. 1961 – separate division of Plant Introduction – Dr. H.B. Singh 1976 – NBPGR Quarantine: 1914 – Destructive Insects and Pest Act. Photosanitary certificate. NBPGR, FRI – Dehradun and Botanical survey of India. Calcutta - Directorate of plant protection, Quarantine and storage - faredabad - good grains & produces imported for human consumption. Germplasm exchange The NBPGR, New Delhi has brought out a brochure 'Guidelines for the exchange of seed/planting material' (National Bureau of Plant Genetic Resources, 1986) and this had  been widely circulated among scientists in India. The guidelines for import of seed/planting material for research purposes have been revised (National Bureau of Plant Genetic Resources, 1989), in view of the enactment of New Seed Development Policy by the Government of India which has also been circulated amongst various scientists/institutes involved. The issuance of 'Import Permit' has been made mandatory by the NBPGR for import of all seed/planting material for research purposes. The salient features of the procedure are described below. Import All requests for indenting germplasm from abroad are to be made to the NBPGR giving specific details of the required material, stating the source/country as well as address of organisation/scientist through a prescribed application so that the Import Permit is issued and sent to concerned scientist(s) for sending the same to exporting organisation or the Bureau be requested to persue the import of desired material(s) from abroad. When requests are sent directly by an individual scientist to any foreign source without an 'Import Permit', the NBPGR needs to be kept informed of such requests for the issuance of 'Import Permit'. The concerned scientist/organisation abroad is advised to take into consideration the following requirements for mailing the material to India. 1. Only healthy, viable and clean seed material (free from soil, pests, pathogens and weeds) are to be forwarded without any seed treatment so as to facilitate proper quarantine examination. It may, however, be fumigated, if considered necessary. 2. The material is required to be accompanied with an 'Import Permit' and 'Phytosanitary Certificate' with additional declaration, if any, based on crop inspection certifying that the material is free from particular pathogen(s)/insect(s). Preferably, two copies of the phytosanitary certificate, one inside the package and the other affixed outside for use by the quarantine authorities are required. It should further be ensured that the package of seed/planting material must be addressed to the Director, NBPGR, New Delhi, who has to take delivery of the seed/planting material and conduct quarantine examination. 3. The seed/planting material should not be sent to any scientist by name directly, since one point entry is necessary to have proper monitoring for quarantine requirements, for documentation of passport data and national accessioning (E.C. Number assignment referring to Exotic Collection). 4. The seed may preferably be sent by first class air mail addressed to the Director, National Bureau of Plant Genetic Resources, Pusa Campus, New Delhi - 110012. 5. The perishable plant propagules (scion/woods, budwoods, plant rhizomes, suckers, etc.) may preferably be sent by airfreight through any commercial airlines operating between source country and the Indira Gandhi International Airport, New Delhi so as to avoid delay in receipt and clearance. If unavoidable, the material can be sent on charge collect basis. An advance intimation of the despatch of such perishable materials to the NBPGR will help in prompt receipt and quick clearance of the material soon after its arrival. This will also avoid payment of demurrage charges. However, in case it is not possible to send by air freight, the same could be sent by courier service. 6. The sender should be requested to give full particulars of the seed/planting material along with the address of the concerned scientist to whom the material is to be made available after quarantine clearance by the Bureau. 7. Germplasm should be obtained in small quantities (3000 to 4000 seeds only) and, in case of vegetative materials, it should not exceed six scion woods, rhizomes, etc., while in case of rooted plants, the number should be kept to the minimum (1-2 plants each). Efforts should be made to avoid repeat introductions. When requests are routed through the NBPGR, this aspect is taken care of since supply of the required seed/planting material may possibly be arranged from sources within India, depending on its availability. Export Exchange of germplasm involves not only introductions but also the supply of seed and other materials to collaborating scientists/organisations abroad. While responding to such requests, the following guidelines are to be followed: 1. Requests for seed/planting material received from concerned organisations/agencies abroad have to be forwarded to the NBPGR with relevant information so that prompt decision on the supply of desired materials could be taken. 2. Despatch of the seed/planting materials is also to be channelised through the Bureau so that prompt inspection of the material could be done from quarantine angle and phytosanitary certificate be issued. 3. Only the healthy seed material (free from diseases, pests, weeds, soil clods, plant debris, etc.) should be sent to the Bureau in small quantity along with full details of the material(s) and the name and address of the recipient. Quarantine clearance and despatch normally takes about 7 to 10 days. 4. No seed dressing with insecticides or fungicides be given while despatching the seed to the Bureau. Quarantine: It is a strategy of control to prevent the spread of pests and diseases. It covers all regulatory actions taken to exclude animal or plant pests or pathogens from a site, area, country, or group of countries. For example, when animal or plant genetic resources are imported from another country or region, there is a risk that they may contain or carry pests or pathogens that could be damaging to agriculture. For this reason, countries use quarantine practices to protect their agriculture and living natural resources from potential damage or destruction Quarantine is usually a government responsibility, and the manner in which quarantine is executed differs among nations. National agencies responsible for plant quarantine may have other responsibilities, such as domestic pest control; research; pesticide registration, safety, and residue monitoring; or seed quality and labeling. - Lec 5: Modes of reproduction – sexual – asexual - self and cross fertilization – significance of pollination Modes of Reproduction Knowledge of the mode of reproduction and pollination is essential for a plant breeder, because these aspects help in deciding the breeding procedures to be used for the genetic improvement of a crop species. Choice of breeding procedure depends on the mode of reproduction and pollination of a crop species. Reproduction refers to the process by which living organisms give rise to the offspring of similar kind (species). In crop plants, the mode of reproduction is of two types: viz. 1) sexual reproduction and 2) asexual reproduction I. Sexual reproduction Multiplication of plants through embryos which have developed by fusion of male and female gametes is known as sexual reproduction. All the seed propagating species belong to this group. Sporogenesis Production of microspores and megaspores is known as sporogenesis. In anthers, microspores are formed through microsporogensis and in ovules, the megaspores are formed through megasporogenesis. Microsporogenesis The sporophytic cells in the pollen sacs of anther which undergo meiotic division to form haploid i.e., microspores are called microspore (MMC) or pollen mother cell (PMC) and the process is called microsporogenesis. Each PMC produce four microspores and each microspore after thickening of the wall transforms into pollen grain. Megasporogenesis A single sporophytic cell inside the ovule, which undergo meiotic division to form haploid megaspore, is called megaspore mother cell (MMC) and the process is called megasporogenesis. Each MMC produces four megaspores out of which three degenerate resulting in a single functional megaspore. Gametogenesis The production of male and female gametes in the microspores and megaspores is known as gametogenesis. Microgametogenesis  This is nothing but the production of male gametes or sperm. On maturation of the pollen, the microspore nucleus divides mitotically to produce a generative and a vegetative or tube nucleus. The pollen is generally released in this binucleate stage. The reach of pollen over the stigma is called pollination. After the pollination, the pollen germinates. The pollen tube enters the stigma and travels down the style. The generative nucleus at this phase undergoes another mitotic division to produce two male gametes or sperm nuclei. The pollen along with the pollen tube possessing a pair of sperm nuclei is called microgametophyte. The pollen tube enters the embryo sac through micropyle and discharges the two sperm nuclei. Megagametogenesis The nucleus of the functional megaspore undergoes three mitotic divisions to produce eight or more nuclei. The exact number of nuclei and their arrangement varies from one species to another. The megaspore nucleus divides thrice to produce eight nuclei. Three of these nuclei move to one pole and produce a central egg cell and two synergid cells on either side. Another three nuclei migrate to the opposite pole to develop into three antipodal cells. The two nuclei remaining in the center, the polar nuclei, fuse to form the secondary nucleus. The megaspore thus develops into a mature female gametophyte called megagametophyte or embryo sac. The development of embryo sac from a megaspore is known as megagametogeneis. The embryo sac generally contains one egg cell, two synergids with the apparent function of guiding the sperm nucleus towards the egg cell and three antipodals which forms the prothalamus cells and one diploid secondary nucleus. Fertilization The fusion of one of the two sperms with the egg cell producing a diploid zygote is known as fertilization. The fusion of the remaining sperm with the secondary nucleus leading to the formation of a triploid primary endosperm nucleus is termed as triple fusion. The primary endosperm nucleus after several mitotic divisions develops into mature endosperm, which nourishes the developing embryo. II. Asexual reproduction Multiplication of plants without the fusion of male and female gametes is known as asexual reproduction. Asexual reproduction can occur either by vegetative plant parts or by vegetative embryos which develop without sexual fusion (apomixis). Thus asexual reproduction is of two types: viz. a) vegetative reproduction and b) apomixis. Vegetative reproduction refers to multiplication of plants by means of various vegetative plant parts. Vegetative reproduction is again of two types: viz. i) Natural vegetative reproduction and  ii) Artificial vegetative reproduction. Natural vegetative reproduction In nature, multiplication of certain plants occurs by underground stems, sub aerial stems, roots and bulbils. In some crop species, underground stems (a modified group of stems) give rise to new plants. Underground stems are of four types: viz. rhizome, tuber, corm and bulb. The examples of plants which reproduce by means of underground stems are given below: Rhizome: Turmeric (Curcuma domestica), Ginger (Zingiber officinale) Tuber: Potato (Solanum tuberosum) Corm: Arvi (Colocasia esculenta), Bunda (C. antiquorum) Bulb: Garlic (Allium sativum), onion (A. cepa) Rhizome: Turmeric Tuber: Potato Bulb: Onion Sub aerial stems include runner, sucker, stolon, etc. These stems lead to vegetative reproduction in mint (Mentha sp) rose, strawberry, banana, etc. Bulbils are modified forms of flower. They develop into plants when fall on the ground. Bulbils are founding garlic. Artificial vegetative reproduction Multiplication of plants by vegetative parts through artificial method is known as artificial vegetative reproduction. Such reproduction occurs by cuttings of stem and roots, and by layering and grafting. Examples of such reproduction are given below: Stem cuttings: Sugarcane (Saccharum sp.) grapes (Vitis vinifera), roses, etc. Root cuttings: Sweet potato, citrus, lemon, etc. Layering and grafting are used in fruit and ornamental crops. Apomixis Apomixis refers to the development of seed without sexual fusion (fertilization). In apomixis embryo develops without fertilization. Thus apomixis is an asexual means of reproduction. Apomixis is found in many crop species. Reproduction in some species occurs only by apomixis. This apomixis is termed as obligate apomixis. But in some species sexual reproduction also occurs in addition to apomixis. Such apomixis is known as facultative apomixis. There are four types of apomixis: viz. 1) parthenogenesis, 2) apogamy, 3) apospory and 4) adventive embryony. 1. Parthenogenesis. Parthenogenesis refers to development of embryo from the egg cell without fertilization. 2. Apogamy. The origin of embryo from either synergids or antipodal cells of the embryosac is called as apogamy. 3. Apospory. In apospory, first diploid cell of ovule lying outside the embryosac develops into another embryosac without reduction. The embryo then develops directly from the diploid egg cell without fertilization. 4. Adventive embryony. The development of embryo directly from the diploid cells of ovule lying outside the embryosac belonging to either nucellus or integuments is referred to as adventive embryony. Modes of Pollination The process by which pollen grains are transferred from anthers to stigma is referred as pollination. Pollination is of two types: viz. 1) Autogamy or self pollination and 2) Allogamy or cross pollination. I. Autogamy Transfer of pollen grains from the anther to the stigma of same flower is known as autogamy or self pollination. Autogamy is the closest form of inbreeding. Autogamy leads to homozygosity. Such species develop homozygous balance and do not exhibit significant inbreeding depression. Mechanism promoting self-pollination 1. Bisexuality Presence of male and female organs in the same flower is known as bisexuality. The presence of bisexual flowers is a must for self pollination. All the self pollinated plants have hermaphrodite flowers. 2. Homogamy Maturation of anthers and stigma of a flower at the same time is called homogamy. As a rule, homogamy is essential for self-pollination. 3. Cleistogamy When pollination and fertilization occur in unopened flower bud, it is known as cleistogamy. It ensures self pollination and prevents cross pollination. Cleistogamy has been reported in some varieties of wheat, barley, oats and several other grass species. 4. Chasmogamy Opening of flowers only after the completion of pollination is known as chasmogamy. This also promotes self pollination and is found in crops like wheat, barley, rice and oats. 5. Position of Anthers  In some species, stigmas are surrounded by anthers in such a way that self pollination is ensured. Such situation is found in tomato and brinjal. In some legumes, the stamens and stigma are enclosed by the petals in such a way that self pollination is ensured. Examples are greengram, blackgram, soybean, chickpea and pea. II. Allogamy Transfer of pollen grains from the anther of one plant to the stigma of another plant is called allogamy or cross pollination. This is the common form of outbreeding. Allogamy leads to heterozygosity. Such species develop heterozygous balance and exhibit significant inbreeding depression on selfing. Mechanism promoting cross-pollination 1. Dicliny It refers to unisexual flowers. This is of two types: viz. i) monoecy and ii) dioecy. When male and female flowers are separate but present in the same plants, it is known as monoecy. In some crops, the male and female flowers are present in the same inflorescence such as in mango, castor and banana. In some cases, they are on separate inflorescence as in maize. Other examples are cucurbits, grapes, strawberry, cassava and rubber. When staminate and pistillate flowers are present on different plants, it is called dioecy. It includes papaya, date palm, spinach, hemp and asparagus. 2. Dichogamy (from the Greek dikho-apart and gamous-marriage) It refers to maturation of anthers and stigma of the same flowers at different times. Dichogamy promotes cross pollination even in the hermaphrodite species. Dichogamy is of two types: viz. i) protogyny and ii) protandry. When pistil matures before anthers, it is called protogyny such as in pearl millet. When anthers mature before pistil, it is known as protandry. It is found in maize, sugarbeet and several other species. 3. Heterostyly When styles and filaments in a flower are of different lengths, it is called heterostyly. It promotes cross pollination, such as linseed. 4. Herkogamy Hinderance to self-pollination due to some physical barriers such as presence of hyline membrane around the anther is known as herkogamy. Such membrane does not allow the dehiscence of pollen and prevents self-pollination such as in alfalfa. 5. Self incompatibility  The inability of fertile pollens to fertilize the same flower is referred to as self incompatibility. It prevents self-pollination and promotes cross pollination. Self incompatibility is found in several crop species like Brassica, Radish, Nicotiana, and many grass species. It is of two types sporophytic and gametophytic. 6. Male sterility In some species, the pollen grains are non functional. Such condition is known as male sterility. It prevents self-pollination and promotes cross pollination. It is of three types: viz. genetic, cytoplasmic and cytoplasmic genetic. It is a useful tool in hybrid seed production. Study of floral biology and aforesaid mechanisms is essential for determining the mode of pollination of various crop species. Moreover, if selfing has adverse effects on seed setting and general vigour, it indicates that the species is cross pollinated. If selfing does not have any adverse effect on these characters, it suggests that the species is self-pollinated. The percentage of cross pollination can be determined by growing a seed mixture of two different varieties together. The two varieties should have marker characters say green and pigmented plants. The seeds are harvested from the recessive (green) variety and grown next year in separate field. The proportion of pigmented plants in green variety will indicate the percentage of out crossing or cross pollination. Significance of pollination The mode of pollination plays an important role in plant breeding. It has impact on five important aspects: viz. 1) gene action, 2) genetic constitution, 3) adaptability, 4) genetic purity and 5) transfer of genes. Classification of crop plants based on mode of pollination and mode of reproduction Mode of pollination and reproduction Examples of crop plants A. Autogamous Species 1. Seed Propagated Rice, Wheat, Barley, Oats, Chickpea, Pea, Cowpea, Lentil, Green gram, Black gram, Soybean, Common bean, Moth bean, Linseed, Sesame, Khesari, Sunhemp, Chillies, Brinjal, Tomato, Okra, Peanut, etc. 2. Vegetatively Propagated Potato B. Allogamous Species 1. Seed Propagated Corn, Pearlmillet, Rye, Alfalfa, Radish, Cabbage, Sunflower, Sugarbeet, Castor, Red clover, White clover, Safflower, Spinach, Onion, Garlic, Turnip, Squash, Muskmelon, Watermelon, Cucumber, Pumpkin, Kenaf, Oilpalm, Carrot, Coconut, Papaya, etc. 2. Vegetatively propagated Sugarcane, Coffee, Cocoa, Tea, Apple, Pears, Peaches, Cherries, grapes, Almond Strawberries, Pine apple, Banana, Cashew, Irish, Cassava, Taro, Rubber, etc. C. Often Allogamous Species Sorghum, Cotton, Triticale, Pigeonpea, Tobacco. Genetic consequences of self and cross-pollination S.No. Self-Pollination Cross-Pollination 1. Self pollination leads to a very rapid increase Cross pollination preserves and in homozygosity. Therefore, populations of promotes heterozygosity in a self – pollinated species are highly population. Cross pollinated species homozygous. are highly heterozygous and show mild to severe inbreeding depression and a considerable amount heterosis 2. Self pollinated species do not show The breeding methods in such inbreeding depression, but may exhibit species aim at improving the crop considerable heterosis. species without reducing heterozygosity to an appreciable degree 3. The aim of breeding methods generally is to Usually hybrid or synthetic varities develop homozygous varieties. The are the aim of breeder wherever the inbreeding mechanisams are generally under seed production of such varieties is precise genetic control, but can be influenced economically feasible. by both the genetic background as well as the environment. Lec 6. Self incompatibility – classifications – mechanisms – application – measures to overcome and limitations SELF INCOMPATABILITY Self incompatibility and sterility are the two mechanisms which encourage cross pollination. More than 300 species belonging to 20 families of angiosperms show self incompatibility Definition  In self incompatible plants, the flowers will produce functional or viable pollen grains which fail to fertilize the same flower or any other flower of the same plant. a) Self incompatible pollen grain may fail to germinate on the stigmatic surface. b) Some may germinate but fails to penetrate the stigmatic surface c) Some pollen grains may produce pollen tube which enters through stigmatic surface but its growth will be too slow. By the time the pollen tube enters the ovule the flower will drop. d) Some time fertilization is effected but embryo degenerates early. Reason Self incompatibility is appeared to be due to biochemical reaction, but precise nature of these reactions is not clearly understood. Classification of self incompatibility According to Lewis (1954) the self incompatibility is classified as follows. Self incompatibility Heteromorphic system Homomorphic system Distyly Tristyly Gametophytic System Sporophytic System Heteromorphyic system In this case there will be difference in the morphology of the flowers. For example in primula there are two types of flowers namely PIN and THRUM. PIN flowers have long style and short stamens while THRUM flowers have short style and long stamens. This type of difference is known as Distyly TRISTYLY is known in some plants like Lythrum. In this case the style of the flower may be either short, long or medium length. In case of distyly the only compatible mating is between PIN and THRUM. The relative position of anthers is determined by single gene S/s. The recessive ss produces PIN and heterozygotes Ss produces THRUM. Homozygous dominant SS is lethal and do not exist. The incompatibility reaction of pollen is determined by the genotype of the plant producing them. Allele S is dominant over s. This system is also known as heteromorphic - sporophytic system. Pollen grains produced by PIN flowers will be all s in genotype as well as in incompatibility reaction. Where as THRUM flowers will produce two types of gametes S and s but all of them would be S phenotypically. The mating between PIN and THRUM would produce Ss and ss progeny in equal frequencies. This system is of little importance in crop plants. It occurs in sweet potato and buck wheat. Mating Progeny Phenotype Genotype Genotype Phenotype Pin x Pin ss x ss Incom. mating - Pin x Thrum ss x Ss 1 ss : Ss 1 Thrum 1 Pin Thrum x Pin Ss x ss 1 Ss : ss 1 Thrum 1 Pin Thrum x Thrum Ss x Ss Incom. mating - Homomorphic System Here the incompatibility is not associated with morphological difference among flower. The incompatibility reaction of pollen may be controlled by the genotype of the plant on which it is produced – (Sporphytic control) or by its own genotype – (Gametophytic control). Gametophytic System First discovered by East and Mangelsdorf in 1925 in Nicotiana sanderae. Here the incompatible reaction of pollen is determined by its own genotype and not by the genotype of the plant on which pollen is produced. Generally the incompatibility reaction is determined by a single gene having multiple allele. E.g.Trifolium Nicotiana, Lycopersicon, Solanum, Petunia. Here Codominance is assumed Genotype of Plant S1 S2 S3 S4 (Sporophyte) Genotype of gametes S1 S2 S3 S4 Incompatible reaction of pollen S1 S2 S3 S4 Incompatible reaction Of style S1 S2 S3 S4 Mating S1S2 x S1 S2 - Fullly Incompatible S1S2 x S1 S3 - Partially compatible  S1S2 x S3 S4 - Fully compatible. Sporophytic System Here also the self incompatibility is governed by a single gene S with multiple alleles. More than 30 alleles are known in Brassica oleracea. Here dominance is assumed. The incompatibility reaction is determined by the genotype of the plant on which pollen grain is produced and not by the genotype of the pollen. This system is more complicated. The allele may exhibit dominance, co-dominance or competition. This system was first reported by Hugues and Babcock in 1950 in Crepis foetida and by Gerstal in Parthenium argentatum. The sporophytic system is found in radish, brassicas and spinach. Lewis has summarized the characteristics of sporophytic system as follows. 1. There are frequent reciprocal differences. 2. Incompatibility can occur with female parent 3. A family can consist of three incompatibility groups. 4. Homozygotes are a normal part of the system 5. An incompatibility group may contain two genotypes. MACHANISM OF SELF INCOMPATABILITY This is quite complex and is poorly understood. The various phenomena observed in Self Incompatibility is grouped in to three categories. a) Pollen - Stigma interaction b) Pollen tube - Style interaction. c) Pollen tube - Ovule interaction. a) Pollen - Stigma interaction : This occurs just after the pollen grains reach the stigma and generally prevents pollen from germination. Prviously it was thought that binucleate condition of pollen in gamatophytic system and trinucleate condition in sporophytic system was the reason for self incompatability. But later on it was observed that they are not the reason for S1. Under homomorphic system of incompatability there are differences in the stigmatic surface which prevents pollen germination. In gametophytic system the stigma surface is plumose having elongated receptive cells which is commonly known as wet stigma. The pollen grain germinates on reaching the stigma and incompatability reaction occurs at a later stage. In the sporophytic system the stigma is papillate and dry and covered with hydrated layer of protein known as pellicle. This pellicle is involved in incompatability reaction. With in few minutes of reaching the stigmatic surface the pollen releases an exince excudate which is either protein or glycero protein. This reacts with pellicel and induces callose formation which further prevents the growth of pollen tube. Pollen - Stigma interaction Gametophytic Sporophytic System System Stigma surface Plumose Commonly Stigma surface Papillate and dry. Covered with known as wet Stigma hydrated layere of protein known as pellicle which involves in incompatibility reaction. Pollen grain germinates and Pollen grain releases exine exudate which is incompatibility reaction occurs at a protein or Glycero-protein. later stage. This protein reaction with pellicle and induces callose formation and arrests growth of pollen type. b) Pollen Tube - Style interaction : Pollen grains germinate and Pollen tube penetrates the stigmatic surface. But in incompatible combinations the growth of pollen tube is retarded with in the style as in Petunia, Lycopersicon, Lilium. The protein and poly saccharine synthesis in the pollen tube stops resulting in bursting up of pollen tube and leading to death of nuclei. c) Pollen tube - Ovule interaction : In Theobroma cacao pollen tube reaches the ovule and fertilisation occurs but the embryo degenerates later due to some biochemical reaction. Relevance of Self incompatibility in Plant Breeding : Self incompatibility may be used for Hybrid seed production. a) By planting two self incompatible but cross compatible varieties alternatively seeds obtained from both the lines are hybrids. b) Alternatively by planting a self incompatible variety along with self compatible variety, the seeds obtained from self incompatible line will be a hybrid. Hybrid seed production was made in brassicas, clover, Trifolium Solanaceous and Asteraceae crops. But there are certain difficulties in this. a) Production and maintenance of inbred line by hand pollination is tedious and costly. b) Continuos selfing leads to break down of self incompatibility and self fertile lines will appear. c) Environmental factors such as high temperature and high humidity reduce self incompatibility. d) Bees often prefers to stay with in particular parental line which in turn increases the proportion of selfed seed. Elimination of Self incompatibility : 1) In a single gene gametophytic system by doubling the chromosome number we can elimate self incompatibility. 2) By induced mutagenesis to produce self fertile lines. 3) By transferring self compatible alleles from related species thro’ back cross breeding. Overcoming Self incompatibility 1. By bud pollination : Application of matured pollen to immature stigma. 2. By surgical technique : Removal of the stigmatic surface E.g. Brassicas or removal of style E.g. Petunias. 3. End of season pollination : In some cases self incompatibility is reduced towards the end of flowering period. Pollination at that time may be successful. 4. Use of high temperature : Exposure of pistil to 600C will induce pseudo fertility. 5. Irradiation :Grafting : Grafing of a branch to another branch.Double pollination : Application of a mixture of incompatible and compatible pollen grains. Lec 7 -Sterility – male sterility – introduction – classification – CMS,GMS,CGMS - inheritance and applications MALE STERILITY Male sterility is characterized by nonfunctional pollen grains, while female gametes function normally. It occurs in nature sporadically. Morphological features of male sterility: The male sterility may be due to mutation, chromosomal aberrations, cytoplasmic factors or interaction of cytoplasmic and genetic factors. Because of any of the above reasons the following morphological changes may occur in male sterile plants. 1. Viable pollen grains are not formed. The sterile pollen grains will be transparent and rarely takes up stain faintly. 2. Non dehiscence of anthers, even though viable pollens are enclosed within. This may be due to hard outer layer which restrict the release of pollen grains. 3. Androecium may abort before the pollen grains are formed. 4. Androecium may be malformed, thus there is no possibility of pollen grain formation. Kinds of male sterility, maintenance and uses: Male sterility may be conditioned due to cytoplasmic or genetic factors or due to interaction of both. Environment also induces male sterility. Depending on these factors male sterility can be classified in to a) Cytoplasmic male sterility (CMS) b) Genetic male sterility (GMS) i) Environmental induced male sterility which is again sub divided in to i) TGMS (Theromosensitive) Two line breeding ii) PGMS (Photo sensitive) ii) Transgenic male sterility c) Cytoplasmic-genetic male sterility (CGMS) (Three line breeding, A , B and R line) A line or MS line: This term represents a male sterile line belonging to any one of the above categories. The A line is always used as a female parent in hybrid seed production. B line or maintainer line: This line is used to maintain the sterility of A line. The B line is isogenic line which is identical for all traits except for fertility status. R line and restoration of fertility: It is otherwise known as Restorer line which restores fertility in the A line. The crossing between A x R lines results in F1 fertile hybrid seeds which is of commercial value. 1. Cytoplasmic Male Sterility (CMS): It occurs due to the mutation of mitochondria or some other cytoplasmic factors outside the nucleus. Nuclear genes are not involved here. There is considerable evidence that gene or genes conditioning cytoplasmic male sterility. Particularly in maize DNA reside in mitochondria and may be located in a plasmid like element. Genetic structure f Sterile Maintenance x f F A line sterile B line fertile f sterile Since mother contributes the cytoplasm to the offspring, the sterility is transferred to the F1 Uses: Since there are no R lines available, this type of sterility is useful only in crops where seed is not the end product. For example in onion and many ornamental plants the hybrids developed exhibit maximum hybrid vigour with respect to longer vegetative duration and larger flower size and larger bulb size. In certain ornamental species, or in species where a vegetative part is of economic value. Cytoplasmic male sterility has successfully been exploited in maize for producing double cross hybrids. GENETIC MALE STERILITY : (GMS) Genetic male sterility is normally governed by nuclear recessive genes ms ms. Exception to this is safflower where male sterility is governed by dominant gene Ms Ms. This type of male sterility is used in Redgram and Castor for production of hybrids. Genetic structure : A line ms ms In Redgram there are number of GMS lines are available. E.g. Ms Co5, Ms T21 Maintenance : In genetic male sterility, the sterile lien will be maintained from heterozygous condition. The genetic structure of heterozygous line will be. Ms ms When this heterozygous line is grown in the field it will segregate in the ratio of 1 Fertile : 1 sterile. Sterile Fertile ms Ms ms ms 1 : 1 The pollen from the Fertile line will pollinate the sterile line and as a result seed set will be there in the sterile line. These seeds are to be harvested and used for hybrid seed production. For hybrid seed production, the seeds collected from sterile plants will be grown using double the seed rate since it will segregate in the ratio of 1 fertile : 1 sterile line. At the time of flowering, the fertile line will be identified by yellow plumpy anthers and removed from the field. Only the sterile line will remain in field. These will be pollinated by the R line and the F1 obtained will be hybrid redgram. Utilisation: Hybrid Development. Eg: Redgram Ms T21 x ICPL 87109 A line R line ms Ms F ms F Ms Ms F ms Hybrid  CoRH 1 Utilization in Plant Breeding Genetic male sterility may be used in hybrid seed production. The progeny from ms ms x Ms ms crosses are used as female, and are inter planted with a homozygous male fertile (Ms Ms) pollinator. The genotypes of ms ms and Ms ms lines are identical except for the ms locus, i.e., they are isogenic ; they are known as male sterile (A) and maintainer (B) lines, respectively. The female line would, therefore, contain both male sterile and male fertile plants ; the latter must be identified and removed before pollen shedding. This is done by identifying the male fertile plants in seedling stage either due to the pleiotropic effect of the ms gene or due to the phenotypic effect of a closely-linked gene. Pollen dispersal from the male (pollintor) line should be good for a satisfactory seed set in the female line. however, generally pollen dispersal is poor and good, closely-linked markers are rare. Rouging of male fertile plants from the female lines is costly as a result of which the cost of hybrid seed is higher. Due to these difficulties, genetic male sterility has been exploited commercially only in a few countries. In USA, it is being successfully used in Castor. In India, it is being used for hybrid seed production of arhar by some private seed companies, e.g., Maharashtra Hybrid Seed Co. Ltd., India, produced and sold 50 Q seed of a hybrid variety of arhar, Suggestions have been made for its use in several other crops, e.g., Cotton, barley, tomato, sunflower, cucurbits etc., but it is not yet practically feasible. DIFFICULTIES IN USE OF GMS 1. Maintenance of GMS requires skilled labour to identify fertile and sterile line. Labelling is time consuming and costly 2. In hybrid seed production plot identification of fertile line and removing them is costly. 3. Use of double the seed rate of GMS line is costly. 4. In crops like castor high temperature leads to break down of male sterility. CYTOPLASMIC – GENEIC MALE STERILITY This is a case of cytoplasmic male sterility where dominant nuclear gene restores fertility. This system is utilised for the production of hybrids in bajra, jowar, maize, rice, wheat and many other crops. Genetic Structure A line ms ms Male sterile. Maintenance A line B line ms x ms S ms F ms sterile Fertile ms S ms Male sterile line The A line which is male sterile is maintained by crossing it with isogenic B line which is also known as maintainer line. The B line is similar to that of A line in all characters (isogenic) except fertile cytoplasm. UTILISATION : The male sterile. A line is crossed with R line ( Restorer) Which restores fertility in F1. A line R line ms Ms S ms Ms F Sterile Fertile Ms S ms Hybrid Fertile DIFFERENT TYPES OF MATING IN CGMS LINE ms ms ms S ms x F ms _____ S ms Sterile Fertile Sterile ms Ms Ms S ms x S/F Ms ______ S ms Sterile Fertile Fertile ms Ms S ms x S/F ms Ms ms S ms and S ms Fertile Sterile. Transfer of Male Sterility from Exotic lines to Nature lines: Most of the times the MS lines obtained from other countries may not be suitable to our condition. Examples are: Crop Source of cytoplasm Drawbacks Maize Texas Cytoplasm Susceptible to Helminthosporium leaf blight Sorghum Combined kafir Black glumes and chalky endosperm Pearlmillet Tift 23 A (Tifton) Susceptible to Green ear & downy mildew Rice Wild abortive incomplete panicle exertion Sunflower H petiolaris, H gigantis Tobacco Microcephalan Reduced vigour in F1 hybrids Wheat Aegilops caudata Susceptible to pistiloidy Due to these drawbacks, the well adapted local lines should be converted into male sterile lines. This can be done by repeated back crossing of the local lines to the exotic MS lines. Transfer of Male Sterility to a New Strain – back cross breeding Maintenance of Male Sterile Line or A line: Since A line does not produce pollen, seed is not formed for maintaining A line. It has to be crossed with its fertile counterpart having similar nuclear genes with fertile cytoplasm which is known as B-line. Production of Hybrid seed: For production of hybrid seed, A-line has to be kept as female parent and the pollen parent should posses the restorer genes in order to induce fertility and seed development in the next generation. Such line is known as restorer line and denoted as ‘ R'line. The A line & R line should be of different genetic constitution and should be able to give maximum heterosis Limitations of CGMS lines. 1. Fertility restoration is a problem. E.g. Rice. 2. Seed set will be low in crops like Rice where special techniques are to be adopted to increase seed set. 3. Break down of male sterility at higher temperature. 4. In crops like wheat having a polyploidy series it is difficult to develop effective R line. 5. Undesirable effect of cytoplasm. E.g. Texas cytoplasm in maize became susceptible to Helminthasporium. In bajra Tift 23 A cytoplasm became susceptible to downy mildew. 6. Modifier genes may reduce effectiveness of cytoplasmic male sterility. LINE BREEDING The process of using different lines (genotype) and producing hybrid is known as line breeding. This terminology is used in production of rice hybrids. The different kinds of line breeding are. a) One line method b) Two line method c) Three line method a) One line method of rice breeding : Rice hybrids can be developed and propagated through the following concepts. - Vegetative propagation. This can be done by ratooning followed by stubble planting. - Micropropagation employing tissue culture technique. - Anther culture hybrids. The anthers of F1 hybrid can be cultured and plant lets developed. - Apomictic lines. b) Two line method of rice breeding.  Two line hybrids can be evolved through application of gametocides and use of environmentally induced genic male sterility. To the selected female parent pollen suppressors can be sprayed at the time of flowering so that it will arrest the production of pollen and thus temporary male sterility is induced. The best combiner is used as a male parent and hybrid is produced. The EGMS system is used successfully in china. Both TGMS and PGMS lines were identified. In this system male sterility is mainly controlled by one or two pairs of recessive nuclear genes and has no relation to cytoplasm. In this system only two lines viz. male sterile and Restorer lines are used. Maintainer line is not needed because by growing the male sterile line in suitable atmosphere the sterility is maintained. In this method there is no negative effect due to sterile cytoplasm. Three line method or CGMS System This system nowadays known as CGMS system involving three lines viz. a) Cytoplasmic genic male sterile line. b) Maintainer or B line and c) Restorer line. TRANSFER OF MALE STERILITY OF A NEW STRAIN Lec 8: TGMS, PGMS, Gametocides, Transgenic male sterility and applicationsTemperature Sensitive Genetic Male Sterility (TGMS): Plants are sterile when temperature exceeds 32˚C/24˚C (day /night) and becomes fertile when the temperature is below 24˚C/18˚C (day /night). However, in few cases, sterility is observed at lower temperature and fertility is observed at higher temperatures. Such type of male sterility is referred to as “ Reverse TGMS type”. This can be utilized in tropical and subtropical countries, where there are large temperature differences across locations, regions and seasons and at different attitudes. It is used to development of two – line hybrids. Photoperiod Sensitive Genetic Male Sterility (PGMS): The line is sterile when the photoperiod (day light) exceeds 14 hrs and same line becomes fertile when subjected to photoperiod of < 13 hrs. PGMS is useful and can be deployed in termperate countries where the day length differs considerably during different seasons. TGMS and PGMS are used for development of hybrid rice in China during eighties. Trangenic Genetic male sterility (TrGMS) Transfer of gene into an genome of aan organism by recombinant DNA technology is called transgene. Barnase/Barstar system is good example of transgenic male sterility. Barnase gene of Bacillus amyloliquefaciens encodes an RNase. Barnase gene is driven by TA29 promoter expressed only in tapetum cells causing their degeneration. Transgenic tobacco and Brassica napus plants with Barnase genes where complete male sterile. Another gener Barstar from the same bacterium encodes a protein which is inhibitor of Barnase Rnase. Hence the transgenic plants expressing both Barstar and Barnase are fully male fertile. Barnase gene has been linked with bar gene, which is resistant to specific herbicide phosphinothricin. Male sterile line can be maintained by crossing it with any male fertile line. Resultant progenies are 1:1 sterile: fertile. Fertile can be easily eliminated by herbicide spray. Gametocides/ Chemically Hybridizing Agents Chemical induction of sterility in plants has been of interest since 1950 when the potential for selective male sterility was first demonstrated. Various terms have been used since 1950 to describe chemicals that induce male. These criteria are essential to sterility in plants. The most commonly used maximize the efficiency of hybrid seed term is gametocide (or) selective gametocide. This terminology was introduced by Eaton (1957) who demonstrated the potential of producing Gossypium hirsutum hybrids through the use of sodium-a, ~- dichloro- isobutyrate (FW-450). Over years many investigator have used such terms as male sterilant, selective male sterilant, pollen suppressant, pollenicide and androcide. Later, the term Chemical Hybridizing Agents (CHAs) is used after the entire primary objective is to produce a hybrid. The first reports of chemically induced male sterility were those by Moore (in 1950) and Nylor induced male sterility in maize using Maleic hydrazide (MH). Laibach and Kribban reported that αNAA and ᵝ- IAA increased the proportion of staminate flowers in cucumber (Cucumis sativus). Important CHAs 1. Zinc methyl arsenate and sodium methylarsenate are commercially used. Sodium methyl arsenate has been popular in rice hybrid production (usually at 150 mg/l) as foliar spary 15 days before heading. Due to toxic effect 5 day before heading is more effective. 2. Ethephon (Ethrel) : It is used in barley, mustard, oats etc., 750+4000mg/l and 0.2 to 12kg/ha depending on crop. Ethrel produces some adverse effects like delayed vegetative growth and low female fertility. Etheral spray before meiosis limits its adverse effect on female fertility. 3. Gibberellic Acid (GA3) : It is commonly applicable maize, barley, wheat, rice and sunflower. It should be sprayed before meiosis initiation after meiosis it is in effective. 4. LY195259: It is very effective but negative effects on seed set and seed quality 5. RH0007 (Hybrex) Used commercially in wheat. 0.2 kg/ha Advantages: 1. Any line can be used as female parent. The lengthy and cumbersome production of CMS, GMS and CGMS lines for hybrid seed production becomes unnecessary 2. Any line can be used as female parent and any line can be used as male parent, restorer gene not required 3. Hybrid seed production only based on two lines 4. Maintenance of parental line achieved through selfing. 5. In CHAs F2s are fully fertile. This would allow for commercial cultivation. Limitations: 1. The expression and duration of CHA- induced male sterility is stage specific 2. Vulnerable to prevailing environmental condition 3. Incomplete male sterility might lead to the production of selfed seed on the female parent 4. Many CHAs are toxic to plants and animals 5. Some CHAs eg arsenicals and WL 84811 may produce carryover residual effect in F1 seeds 6. Sme CHAS stimulate neoplamic growth affect human growth 7. CHAs are generally genotype- dose and application stage specific. Lec 9 - Apomixis – introduction - classification-applications; Parthenocarpy and its types. INTRODUCTION:  Apomixis, derived from two greek word “ APO” (away from) and “ mixis” (act of mixing or mingling). It refers to the occurrence of an sexual reproductive process in the place of normal sexual processes involving reduction division and fertilization. In other words apomixis is a type of reproduction in which sexual organs of related structures take part but seeds are formed without union of gametes. Seeds formed in this way are vegetative in origin. When apomixis is the only method of reproduction in a plant species, it is known as obligate apomixis. On the other hand, if gametic and apomictic reproduction occur in the same plant, it is known as facultative apomixis. The first discovery of this phenomenon is credited to Leuwenhock as early as 1719 in Citrus seeds. Apomixis is widely distributed among higher plants. More than 300 species belonging to 35 families are apomictic. It is most common in Grami