ACS 102 Midterm - Modes of Crop Reproduction PDF

ACS 102 MIDTERM Lesson 1 MODES OF REPRODUCTION OF CROP SPECIES AND POLLINATION CONTROL Why is it important to control Pollination?  Types of Pollinators: ACHEMO Anthropophily- Human Chiropterophily- Bats Hydrophily- Water Entomophily- Insects Malaco...

ACS 102 MIDTERM Lesson 1 MODES OF REPRODUCTION OF CROP SPECIES AND POLLINATION CONTROL Why is it important to control Pollination?  Types of Pollinators: ACHEMO Anthropophily- Human Chiropterophily- Bats Hydrophily- Water Entomophily- Insects Malacophily- Snails Ornithophily- Birds  This topic explains the three modes of reproduction of crop species to understand their significance and mechanism. Tackles on what mode of reproduction is employed on a specific crop to obtain their optimum growth and production. On the other hand, breeding is important for acquiring higher yield, resistance to pests and tolerance to environmental stresses.  Plant reproduction is vital for the perpetuation of crop species, breeding is employed for the improvement of crop quality and characteristics to enhance farm productivity. MODES OF REPRODUCTION IN PLANTS The mode of reproduction in crop plants may be broadly grouped into three categories: Sexual, Apomictic and Vegetative. MODES OF REPRODUCTION IN PLANTS I. SEXUAL This process of reproduction involves the fusion of male and female gametes and formation of seed, so it is called the process of amphimixis. Depending on the nature of pollination the plants can be categorized as self-pollinated and cross pollinated. Pollination – is a process by which pollen grains are transferred from anthers to stigma. Two types of pollination: A. Self-pollination or Autogamy transfer of pollen grains from the anther to the stigma of same flower. is the closest form of inbreeding. 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 green gram, black gram, soybean, chickpea and pea. B. Cross-pollination or Allogamy transfer of pollen grains from the anther of one plant to the stigma of another plant. this is the common form of outbreeding. 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: monoecy – when male and female flowers are separate but present in the same plants. 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. dioecy – when staminate and pistillate flowers are present on different plants. 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: protogyny – when pistil matures before anthers, such as in pearl millet. protandry – when anthers mature before pistil, it is found in maize, sugar beet 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.  Mechanism promoting cross- pollination 4. Herkogamy – hindrance 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 a useful tool in hybrid seed production. Significance of Pollination The mode of pollination plays an important role in plant breeding. It has impact on five important aspects: 1. gene action 2. genetic constitution 3. adaptability 4. genetic purity 5. transfer of genes Classification of crop plants based on mode of pollination and mode of reproduction. Mode of pollination Examples of crop plants and reproduction A. Self-pollinated or Autogamous Species Rice, Wheat, Barley, Oats, Chickpea, Pea, Seed Propagated Cowpea, Lentil, Soybean, Common bean, Sesame, Chilies, Brinjal, Tomato, Okra, Peanut, etc. Vegetatively Propagated Potato B. Cross-pollinated or Allogamous Species Seed Propagated Corn, Rye, Alfalfa, Radish, Cabbage, Sunflower, Sugar beet, Spinach, Onion, Garlic, Turnip, Squash, Watermelon, Cucumber, Pumpkin, Oil palm, Carrot, Coconut, Papaya, etc. Vegetatively Propagated Sugarcane, Coffee, Cocoa, Tea, Apple, Pears, Peaches, Cherries, grapes, Almond Strawberries, Pine apple, Banana, Cashew, Cassava, Taro, Rubber, etc. C. Often Allogamous Sorghum, Cotton, Pigeon pea, Tobacco. Species Genetic consequences of self-pollination and cross- pollination. Self-pollination Cross-pollination Self-pollination leads to Cross pollination preserves and promotes a very rapid increase in heterozygosity in a population. Cross pollinated homozygosity. species are highly heterozygous and show mild Therefore, populations to of self-pollinated severe inbreeding depression and a considerable species are highly amount heterosis. homozygous. Self-pollinated species The breeding methods in such species aim at do not show inbreeding improving the crop species without reducing depression, but may heterozygosity to an appreciable degree. exhibit considerable heterosis. The aim of breeding Usually, hybrid or synthetic varieties are the aim methods generally, is to of breeder wherever the seed production of such develop homozygous varieties is economically feasible. varieties. The inbreeding mechanisms are generally under precise genetic control, but can be influenced by both the genetic background as well as the MODES OF REPRODUCTION IN PLANTS II. APOMIXIS – derived from two Greek word "apo" (away from) and "mixis" (act of mixing or mingling). refers to the occurrence of a sexual reproductive process in the place of normal sexual processes involving division and fertilization. a type of reproduction in which sexual organs of related structures take part but seeds are formed without union of gametes. Parthenocarpy- Formation of Fruits without undergoing fertilization. Apomixis Seeds formed in this way are vegetative in origin. The plants produced by apomixis are called apomictic which are of two types: obligate, producing only apomictic embryos, and facultative, producing both apomictic and normal embryos. The first discovery of this phenomenon is credited to Antonie van Leeuwenhoek as early as 1719 in Citrus seeds. Embryo- Is the miniature version of the plant. The embryo is a tiny plant that has a root, a stem, and one or more leaves. Apomixis is the phenomenon where there is no normal fertilization of the egg cell, hence no normal development of embryo from the egg cell. However, embryo may develop from an un-fertilized egg cell or from a cell other than the egg cell within the embryo sac or from the cell outside the embryo sac. Significance of Apomixis Apomictic plants tend to conserve the genetic structure and are also capable of maintaining heterozygote advantages. Due to prohibition of fertilization process, apomixis is the way for exploitation of maternal influence or perpetuation of maternal individuals or maternal properties. MODES OF REPRODUCTION IN PLANTS III. VEGETATIVE OR ASEXUAL In this type of reproduction, the vegetative parts of the plants act as propagule in place of seed. This mode is mostly found in all those plants where there is no seed set, long reproduction cycle and heterozygosity exists.  The following organs can act as propagule: 1. Modified Stem Underground modified stems that are used for propagation: Rhizomes (ginger, turmeric) Bulb Corm (colocasia, yam) (garlic)  The following organs can act as propagule: 1. Modified Stem Underground modified stems that are used for propagation: Tuber Stolon (potato) Sucker (strawberry) (chrysanthemum) The following organs can act as propagule: 2. Stem Cutting In many of the fruit crops the artificially produced clones or stem cuttings are used as propagative material. In sugarcane the nodal portions of stems, in fruit crops like mango, lemon, grapes – the different methods like layering, grafting, budding are applied to get the stem clone. The following organs can act as propagule: 3. Normal or Modified Root Normal roots of wood-apple, citrus and many such trees are used as units for propagation. Modified roots such as tuberous root (sweet potato), fasciculated root (dahlia, asparagus) are used as propagule. The following organs can act as propagule: 4. Bulbils In some plants the flower bud modified into globose bulb which are called bulbils can be used as multiplication unit. Significance of Vegetative Reproduction Asexual or vegetative reproduction leads to perpetuation of the same genotype with great conservation. It is very much advantageous because large number of genetically identical individuals can be obtained irrespective of the degree of heterozygosity of the genotype. At any stage of breeding programme if a breeder gets any desirable clone, it can be maintained through vegetative means. Mutation breeding, i.e., the search for desirable mutants both through natural and artificially induced mutation is very much helpful in case of vegetatively reproducing plants as the sexual reproduction can be avoided.  ACS 102 MIDTERM PRINCIPLES OF BREEDING FOR HIGH YIELDS, PESTS’ RESISTANCE AND TOLERANCE TO ENVIRONMENTAL STRESSES PRINCIPLES OF BREEDING FOR HIGH YIELDS, PESTS’ RESISTANCE AND TOLERANCE TO ENVIRONMENTAL STRESSES 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. PRINCIPLES OF BREEDING FOR HIGH YIELDS, PESTS’ RESISTANCE AND TOLERANCE TO ENVIRONMENTAL STRESSES 1. Increased yield Majority of breeding programmes aims at increased yield. This is achieved by developing more efficient genotypes. Plant breeding is vital to increase the genetic yield potential of all crops. Yields of major crops, for example, Chinese cereal production has increased steadily from 83.4 Mt in 1961 to 474.2 Mt in 2009, accounting for 9.5% of total global cereal production in 1961 and 21.8% in 2009. However, these yield increases are not totally due to the genetic potential of the new crop cultivars but also due to improved agronomic practices (e.g., application of fertilizer, irrigation). Crops have been armed with disease resistance to reduce yield loss. Lodging resistance also reduces yield loss resulting from harvest losses. PRINCIPLES OF BREEDING FOR HIGH YIELDS, PESTS’ RESISTANCE AND TOLERANCE TO ENVIRONMENTAL STRESSES 2. Improving the quality rice -milling, cooking quality, aroma and grain color wheat- milling and baking quality and gluten content pulses -Protein content and improving sulphur containing amino acids PRINCIPLES OF BREEDING FOR HIGH YIELDS, PESTS’ RESISTANCE AND TOLERANCE TO ENVIRONMENTAL STRESSES 3. Elimination of toxic substance Erucic acid in Brassicas Cucurbitacin in cucurbits PRINCIPLES OF BREEDING FOR HIGH YIELDS, PESTS’ RESISTANCE AND TOLERANCE TO ENVIRONMENTAL STRESSES 4. Resistance against biotic and abiotic stresses Biotic stress: Evolving pests and diseases resistant varieties thereby 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. PRINCIPLES OF BREEDING FOR HIGH YIELDS, PESTS’ RESISTANCE AND TOLERANCE TO ENVIRONMENTAL STRESSES 5. Change in maturity duration – evolution of early maturing varieties 6. Improved agronomic characters – production of more tillers – Rice 7. Reducing the plant height to prevent lodging – Rice 8. Photo insensitivity – Sorghum PRINCIPLES OF BREEDING FOR HIGH YIELDS, PESTS’ RESISTANCE AND TOLERANCE TO ENVIRONMENTAL STRESSES 9. Non-shattering nature – Brassicas 10. Synchronized maturity – Pulses