Crop Improvement and Seed Selection PDF

**Crop Improvement and Seed Selection \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_...

**Crop Improvement and Seed Selection \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_** **The objectives of crop improvement other than increase of yield are:** - Development of new varieties adapted to the various growing conditions - Improvement of horticultural characteristics - Development of varieties resistant to pests and diseases and - Improvement of the quality of horticultural products. With the beginning of genetics (the study of heredity and variation in living organisms), is a scientific basis for crop improvement may follow Mendel's Principles or non-Mendelian inheritance. **Mendelian Principles:** **i. Mendel's Principle of Uniformity in F1:** F1 offspring of a monohybrid cross of true-breeding strains resemble only one of the parents, showing the dominant trait. e.g. Smooth seeds (allele S) are completely dominant to wrinkled seeds (alleles). **ii. Mendel's Principle of Segregation:** Recessive characters masked in the F1 progeny of two true-breeding strains, reappear in a specific proportion of the F2 progeny. Two members of a gene pair segregate (separate) from each other during the formation of gametes. **iii. Mendel's Principle of Independent Assortment:** Alleles for different traits assort independently of one another. Genes on different chromosomes behave independently in gamete production. **Overview of gene expression →** **DNA:** deoxyribonucleic acid; Polynucleotide formed from covalently linked Deoxyribonucleotide units. It serves as the store of hereditary information within a cell and the carrier of this information from generation to generation. **RNA:** ribonucleic acid; transcribed DNA which will serve as template for synthesis of protein **POLYPEPTIDE:** a chain of proteins that make up a gene **GENE:** encodes proteins that produce a diverse range of traits or phenotype (observable characteristic); located within the CHROMOSOMES.  **Crop Improvement and Seed Selection \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_** **Seed/Sexual Propagation** *Seed propagation* is the most common method by which plants reproduce in nature because it is easy and cheap. Mostly of the horticultural crops are propagated through sexual propagation. Seed propagation is sometimes termed as *sexual propagation*. Seeds arise from the fusion of male and female gametes to form a single cell or zygote within the ovule of a flower. Disadvantage of using this method for horticultural trees is that plants from seeds tend to grow into taller plants, especially plantation and fruit trees. A *seed i*s a mature ovule that is consists of an embryo, its food reserves and the seed covering called testa or seedcoat. The embryo is the rudimentary plant that is usually the product of fertilization of the egg and sperm cell from a pollen tube. The seed coat originates from the integument of the ovule. The food reserves are contained either in the endosperm or in the fleshy cotyledon, which is a part of the embryo itself. The cotyledons are leaf-like parts and become the first foliar structures. The seeds are attached to the aril, the stalk that is attached to the fruit. The *embryo* is consisting of a radicle, a plumole and hypocotyl. The radicle is the future root, the plumole or epicotyl the future shoot, while the hypocotyl connects the radicle and plumule. The scar that remains after the seed breaks off from its attachment to the other parts of the fruit is called the hilum, while the opening is called micropyle. **Seed Germination** **Seed germination process** is as series of events which takes place when dry quiescent seeds imbibe water resulting in an increase in metabolic activity and the initiation of a seedling from the embryo or the resumption of embryo growth. The success of propagation from seeds depends on how fast the germination process is and how well the young plants grow, whether it is in the field or in the nursery. Providing the requirements of the processes of germination, photosynthesis and respiration at their optimum is necessary. For germination to be rapid therefore: *(a) the embryo must be alive (viable) and non-dormant; (b) moisture must be available and can reach the cotyledons and the endosperms which contain the activating or deactivating hormones and the stored food; (c) oxygen is available and can reach the storage tissues; and (d) temperature is optimum.* There are two types germination namely; epigenous and hypogenous germination. 1. *Epigenous germination* is when the hypocotyl elongates and brings the cotyledons above the ground and 2. *Hypogenous germination* is when epicotyl emerges and the cotyledons remain below the soil surface. **Dormancy** **Seed dormancy** is a physiological condition of a viable seed that prevents germination even in the presence of otherwise favourable germination conditions however; seed quiescence is a condition in which seed cannot germinate because of unfavourable conditions. Dormancy may arise from *(a) physical causes such as presence of mucilage's or hard seedcoat that is impermeable to water and oxygen, (b) physiological causes such as presence of chemical inhibitors which decreases time, inadequacy of growth regulators, (c) light sensitivity and (d) embryo dormancy.* **Types of dormancy** 1. **Primary** a. Exogenous or coat-imposed dormancy -- essential germination components not available b. Endogenous dormancy -- caused by environment during seed development and maturation 2. **Secondary** a. This is imposed by temperature, light/darkness, abnormal amount of water; chemical and gases. **Dormancy technology** a. *Ecodormancy* -- due to one or more unsuitable factors in the environment with non-specific effect b. *Paradormancy* -- due to physical factors or biochemical signals originating externally to affected structure c. *Endodormancy* -- regulated by physiological factors inside affected structure **Hastening Seed Dormancy/Breaking dormancy** *Scarification* -- is any treatment that removes the seedcoat or alters it, making it more permeable to water and air. This can be done mechanically by rubbing into a rough surface or the use of chemicals such as hydrogen peroxide and muriatic acid. **Types of scarification** c. *Physical scarification* -- soaking in water (tap, hot or boiling water) for a specified period of time. d. *Mechanical scarification* -- piercing, rubbing on sandpaper, filing grinding with abrasives e. *Chemical scarification* - treatment with sulphuric acid and organic solvents *Stratification* -- is the placement of seeds between layers of moist sand, soil, or sawdust at high or low temperature so the action of water high and low temperature will soften the seedcoat. The germination of the seeds of abaca is enhanced by this method. *Vernalization* -- is a seed treatment to cold temperature prior to germination. *Hardening* -- is done by gradual exposure to sunlight if the seedlings are kept in shaded area or gradual withdrawal of water and fertilizer. This becomes necessary to avoid transplanting shock. Transplanting shock refers to the temporary set-back in the growth after transplanting. **Asexual/Vegetative propagation** The vegetative propagation involves reproduction from vegetative parts of plants and is possible because the vegetative organs of many plants have the capacity for regeneration. The vegetative parts used can be classified into*: (a) those severed from the mother plant, (b) those still attached to the mother plant, and (c) those attached or united to another rooted plant. There are several reasons for using vegetative propagation.* These are: 1. The resulting plant process of the same characteristics as the mother since vegetative propagation involves no change in genetic make-up of the resulting plant. The exact duplicate of the chromosome system of the mother plant is reproduced during cell division. 2. It also allows reproduction of plants where seed propagation is impossible or difficult, such as in plants that produce no seeds or fruits with seeds do not or take long time to germinate. Examples are banana, pineapple and breadfruit. 3. Vegetative method is more efficient, convenient, and practical to use than seed propagation especially in the case of ornamentals. 4. Vegetatively propagated trees are usually smaller and bear fruits earlier than those grown in seeds. 5. It is also used for diocious plants where male and female plants are obtained among the seedlings coming from the seeds as in rambutan and pili. A conventional method of propagation includes *(a) separation and division, (b) cuttage, (c) layerage, (d) graftage and tissue culture.* A specific method of propagation may be more suitable for a certain species/variety under existing environmental conditions. 1. *Separation and division* involve the use of specialized or modified stems, roots, and plantlets as propagating materials. The specialized organs are the bulb, bulblet, corm, cannel, tuber, tuberous root, rhizome, bulbil, offset, sucker, slip, and the crown. **Separation** Is propagation using naturally detachable organs. It also applies to the process of separating a clump into several portions, each with a root system. The specialized organs are the bulb; bulblet, corm, cannel, tuber, tuberous root, rhizome, bulbil, offset, sucker, slip, and the crown are as follows. a. b. c. d. e. f. g. h. i. j. k. l. m. n. **Division** It is a method of asexual propagation wherein specialized or modified stems and roots are cut into pieces or sections with at least one bud or eye per section. 1. It is a method of vegetative propagation involving regeneration of structural parts in detached vegetative parts under favourable environmental conditions and included to form roots and shoots, thus producing a new independent plant. **Types of cutting** 1. *Root cutting* -- plant species with a natural tendency to send up sprouts or produce adventitious shoots from the roots can be propagated by root cutting. Examples are apple and breadfruit. 2. *Leaf cutting* -- plants with thick and heavy leaves can be propagated by leaf cuttings. This type of cuttings utilizes the leaf blade or leaf blade and petiole, to start a new plant. Examples snake plant, begonia and African violet. 3. *Stem cutting* -- is the most common type of cutting used. To propagate by stem cuttings, segments of a shoot or a branch with lateral or terminal buds are selected. Under favourable conditions, these stem cuttings are capable of developing adventitious roots at their basal portions, eventually producing new plant. These types of stem cutting and these are follows; a. *Hardwood cuttings* -- the propagating material for hardwood cuttings is usually leafless and should come from a branch produced during the previous growing season. Small and weakly growing interior shoots should not be used. The plant from which the branches are taken should be relatively healthy, vigorous and grown under full sunlight. A shoot or branch of moderate size and vigor is the most desirable one. The basal portion of cuttings is planted in the medium. b. *Semi-hardwood cuttings*- cuttings of this type usually taken from partially mature wood, with or without terminals which are healthy, vigorous and growing under full sunlight. Examples are grapes, citrus and passion fruit. c. *Softwood cuttings*- this type generally roots easier and quicker than other types but requires more attention. The cuttings are always made with the leaves intact and handled carefully to prevent wilting like passion fruit. d. *Herbaceous stem cuttings* -- this type of cuttings is treated like softwood cuttings. Herbaceous cuttings root much faster when treated with a root-promoting chemical and grown under high humidity. 2. **Layering** - a propagation method by which adventitious roots are included to a form on a stem while it is still attached to the parent plant, which supplies the nutrients and moisture while the roots of the plants are still forming. Below are the types of layering. a. b. c. d. 3. **Types of graftage** a. b. c. d. e. 4. a. b. c. 4. **Tissue culture techniques other than embryo culture --** can be started from a variety of plant parts which have cells capable of dividing (example: shoot-tip culture; meristem culture and endosperm culture).  **Crop Improvement and Seed Selection \_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_** **General methods of crop improvement** **Activities in plant breeding** 1. - naturally-existing variability a. Teosinte → Modern Corn→ b. c. - primary introduction --introduced variety is released for commercial cultivation without any alteration in the original genotype - secondary introduction --introduced variety subjected to selection or hybridized with local varieties to transfer one or few characters from this variety to the local varieties - creation of new variability **Four most common mating systems used in crop improvement:** 1. **Topcross** 2. **Polycross** 3. **Backcross** Parents: 4. **Hybrid cross** F1 single cross hybrid F1 3-way cross hybrid F1 double cross hybrid **Process in creating new variability in crops:** a. - inbreeding -- mating of individuals related by ancestry; leads to production of homozygous individuals Inbred -- product of inbreeding. Hence, consequently, a homozygous individual - selfing -- mating with oneself; most intense form of inbreeding hence approach to homozygosity is fastest - full sibbing -- crossing between members of selected pairs of plants; full sibs have both parents in common - half sibbing -- crossing one individual with several identified ones; half sibs have one common parent or pollen source - topcross -- cross between an inbred and an open-pollinated variety - testcross -- cross between a plant or line and a tester (tester may be an inbred, hybrid, synthetic, or open-pollinated variety) - backcross -- a cross between a hybrid and one of its parents; also a breeding method based on repeated backcrossing of the F1 (first generation offspring of a cross) and the subsequent generations to the recurrent parent usually to transfer a major trait controlled by one or a few genes from the donor (as the non-recurrent parent) and the recipient (as the recurrent parent). - polycross -- open pollination in isolation among a number of selected genotypes arranged in a manner that promotes random mating - reciprocal cross -- mating of two individuals in which each is used as the male parent in one cross and the female parent on the other - intraspecific cross -- crossing individuals belonging to the same species, ex. variety x variety cross - wide or distant cross -- crossing distantly-related individuals - interspecific -- crossing individuals belonging to different species - intergeneric -- crossing individuals belonging to different genera - Introgressive hybridization -- repeatedly backcrossing interspecific hybrids to one of the parental species leading to the transfer of some genes from one species to another - Barriers to production of distant hybrids: - failure of zygote formation - failure of zygote development - failure of hybrid seeding development - Techniques to overcome barriers to production of distant hybrids - use of bridge species -- species that can successfully cross with both parents - protoplast fusion -- combining protoplasts of the two parents to produce somatic hybrids - embryo rescue -- in vitro culture of young hybrid embryos before their breakdown - grafting - manipulation of ploidy level of either of the two parents in case they differ in ploidy or doubling chromosome number of the hybrid - Terms related to hybridization: - Alien addition line -- carries one chromosome pair from a different species in addition to the normal diploid chromosome complement of the parent species; alien addition chromosome or monosomic alien addition line has only one chromosome (not a pair) from another species. - Alien substitution line -- has one chromosome pair from a different species in place of one chromosome pair of the recipient species; alien substitution monosome or monosomic alien substitution line has a single chromosome (not a pair) from a different species in place of a single chromosome of the recipient species. - Heterosis -- or hybrid vigor; superiority of the F1 hybrid over its parents; may be positive or negative; ex. positive heterosis for yield and negative heterosis for days to maturity; types are: - mid-parent heterosis -- increase or decrease in the performance of the hybrid in comparison with the mid-parent value or average performance of the two parents - heterobeltiosis -- the increase or decrease in the performance of the hybrid in comparison the better parent of the cross combinations - standard heterosis -- the increase or decrease in the performance of a hybrid in comparison with the standard check variety of the region: type of heterosis practically important to breeders - Heterosis is expected to be high when inbreds used in producing the hybrids have high combining abilities - combining ability -- the ability of a genotype (inbred, pureline or synthetic) to transfer its desirable traits to its progeny: - general combining ability (GCA) -- average performance of a strain in a series of crosses; estimated using testers of broad genetic base and identifies mainly additive genetic effects. - Specific combining ability (SCA) -- deviation from performance predicted on the basis of general combining ability of parental lines; estimated by using testers of narrow genetic base and identifies both additive and non-additive gene action - Theories to support heterosis: - dominance hypothesis -- that heterosis is due to the accumulation of favorable dominant genes from the two parents of the hybrid - overdominance hypothesis -- that heterozygotes are more vigorous and productive than either homozygotes. - Inbreeding depression -- loss in vigor due to inbreeding - Mechanisms promoting self-pollination - cleistogamy -- flowers do not open at all ensuring complete self-pollination - chasmogany -- flowers open but only after pollination has taken place - stigmas closely surrounded by anthers - flowers open but stamen and stigma are hidden by other floral organs - stigma when receptive elongate through stamina columns - Mechanisms promoting cross pollination - dicliny or unisexuality -- flowers are either staminate (male) or pistillate (female) - monoecy -- staminate and pistillate flowers occur in the same plant either in the same or in different influorescences. - dioecy -- male and female flowers are present on different plants, the plants in such species are either male or female. - dichogamy -- stamens and pistils of hermaphrodite (perfect bisexual) flowers may mature at different times facilitating cross pollination - protogyny -- pistils mature before stamens - protandry -- stamnes mature before pistils - stigmas are covered with waxy film - self-incompatibility -- failure of pollen from a flower to fertilize the same flower or other flowers on the same plant - male sterility -- absence of functional pollen grains in otherwise hermaphrodite flowers - Systems of pollen control in controlled pollinations/crosses or hybridization - emasculation -- removal of immature anthers (or androecium) from a hermaphrodite flower using clip, hot water or suction/vacuum methods. - male sterility systems -- male gametes not functional but females gametes are fertile - cytoplasmic male sterility -- genes for male sterility in the cytoplasm particularly in the mitochondrion - genetic male sterility -- sterility controlled by a nuclear gene, usually recessive - cytoplasmic-genetic male sterility -- controlled by interaction between genetic factors present in the cytoplasm and nucleus; presence of a male sterility gene in the cytoplasm and a restorer gene in the nucleus results in the latter overcoming the effect of the former to restore fertility - environment-sensitive genetic male sterility (EGMS) -- genetic male sterility system conditioned by environmental factors - photoperiod sensitive genetic male sterility (PGMS) -- responds to photoperiod or duration of day length for expression of pollen sterility and fertility, ex. sterile under long day (\>13.75h) conditions and fertile under short day(\30°C), fertile at lower temperature (\ - physical mutagens -- β rays, α rays, fast and thermal neutrons, x-rays, γ rays, UV radiation - chemical mutagens -- alkylating agents, acridine dyes, base analogues, etc. - Chimera -- an individual with one genotype in some of its parts and another genotype in the others - periclinal chimera -- when the entire outer (outer periclinal) or inner (inner periclinal) layer of shoot apical meristem is affected. Outer layer gives the rise to the dermal system and part of mesophyll while the inner layer produces the rest of the plant - sectorial chimera -- only a part of the outer (outer sectorial) or inner (inner sectorial) layer is affected c. - euploidy -- change in chromosome number involving one or more complete genomes; chromosome number is an exact basic or genomic number, ex. triploids, tetraploids, pentaploids, etc. - autopolyploid -- when all the genomes present in a polyploidy species are identical - allopolyploid -- two or more distinct genomes are present - amphidiploid -- an allopolyploid that has two copies each genome present in it; have regular meiosis - segment allopolyploid -- contains two or more genomes which identical with each other except for some minor differences - aneuploidy -- change in chromosome number involving one or a few chromosomes of a genome; nullisomics, monosomics, trisomics, etc. - Somaclonal variation -- heritable variation for both qualitative and quantitative traits shown by plants regenerated from the tissue and cell cultures - Gametoclonal variation -- heritable variation shown by plants regenerated from pollen or anther culture d. 2. **Selection** -- identification of individuals or lines that are more desirable than others in a heterogeneous population - Natural selection -- change in gene frequencies from one generation to another because of differences in survival and reproductive abilities of parental genotypes in natural populations - Artificial selection -- change in gene frequencies brought about by man as is done in plant breeding where certain individuals or genotypes are not used as parent of the next generation **Modes of selection:** - Stabilizing or normalizing selection -- when adaptive individuals in the populations are selected in a constant environment through the years; keeps the population constant and eliminates the deviants; reduces the variability present in the population - Directional selection -- change towards a particular direction due to changing environments resulting also in change of the genetic constitution of the population; mode observed when breeders do artificial selection - Diversifying or disruptive selection -- opposite of stabilization selection; leads to either formation of subpopulation differing in characteristics or polymorphism in which each genotype is represented by a distinct phenotype **Traits selected for:** - Qualitative traits -- monogenic or oligogenic traits; show discrete or non-continuous variation, controlled by one or few genes, less influenced by the environment - Quantitative traits -- polygenic, metric or measurable traits; show continuous variation; controlled by many genes, highly influenced by environment **Bases of selection:** - Phenotype (P) can be accounted for the genotype (G), the environment € and the interaction between the genotype and the environment (GxE). **Components of phenotypic variance:** - Phenotypic variance -- sum of genotypic variance, environmental variance and GxE variance - Genotypic variance -- sum of additive and non-additive types of gene action a\. additive -- due to individual effects of genes **Intralocus interaction** -- dominance interactions; interaction between alleles in the same locus a\. complete dominance -- heterozygote is equal to the dominant homozygote in value b\. partial dominance -- value of the heterozygote is between the average of the two homozygotes and the value of the dominant homozygote c\. over dominance -- if the heterozygote has a value outside the range of the two homozygotes **Interlocus interaction** -- epistasis; interaction among alleles of different loci - Environmental variance -- effect of the environment on the phenotype and estimated by measuring variation in a genotypically uniform population grown in certain location - GxE interaction -- change in ranking and/or performance of genotypes when grown in different environments; estimated by computing variances of genotypes when grown in number of locations which are environmentally diverse **Heritability** -- potion of the phenotype variation among individuals that is due to genetic differences among them - broad-sense heritability is estimated from the ratio of the total genetic variance to the phenotypic variance - narrow-sense variance -- heritability is estimated from the ratio of the genetic variance to the phenotypic variance **Selection intensity** -- the percentage of individuals selected in a population **Selection differential** -- difference between the mean performance of genotypes selected from a population and the overall population mean **Gain from selection** -- genetic gain, genetic responses from selection, genetic advance from selection; increase in mean performance of a population that is realized with each cycle of selection; estimated based on selection intensity, heritability of the character and the phenotypic variance. **Methods of selection** d. - mass selection -- plants are chosen and harvested on the basis and phenotype and the seeds composited without progeny testing; appropriate for qualitative characters with simple genetic inheritance - pureline selection -- procedure for isolating purelines from a mixed population Pureline -- progeny from self-pollination of a single homozygous plant - pedigree selection -- selection for plants with the desired combination of characters is started in the F2 (product of selfing F1) generation and continued in succeeding generations until genetic purity is reached; requires detailed record-keeping (pedigree records); suited to individual plant selections - bulk population -- seeds harvested in the F2 and succeeding generations are bulked and grown, with selection delayed until the F5 or F6, at which time the segregation will have virtually ceased - single-seed descent -- progenies of the F2 plants are advanced rapidly through succeeding generations from single seeds; selection done at F5 and later generations - doubled haploid -- haploid plants are generated from anthers of F1 plants or by other means, and the chromosomes of the haploid plants are doubled with colchicine to produce homozygous diploid plants; selection may start in early generation plants e. **Cross-pollinated crops** Population improvement approach -- increasing the frequency of genes in the population of the desire breeding objective - recurrent selection -- any breeding system designed to increase the frequency of the desired alleles for particular quantitatively inherited character by repeated cycles of selection - mass selection -- individual plants are chosen for their desirable traits and the seeds harvested from the selected plants are bulked to grow in the following generation without any form of progeny evaluation - half-sib family selection -- new population is constituted by compositing half-sib lines selected from progeny performance rather than phenotypic appearance; ear-to-row selection; without pollen control - full-sib family selection -- crosses are made between selected pairs of plants in the source population, with the crossed seeds used for progeny tests and for reconstituting of new population; measure the combining ability from mating specific pairs of plants - S1 progeny selection -- utilized to evaluate selected plants from an open-pollinated source S1 is the progeny following self-pollination of plants in an open-pollinated population or in the F2 following a cross - reciprocal recurrent selection -- improves two populations simultaneously; plants are selected in each of the two populations, with the selected plants of one population being self and outcrossed as the tester to the selected plants in the other population; remnant seed from the plants with superior testcross progenies are grown and intercrossed to reconstitute the two populations. 3. Sequences in the conduct of yield tests: - observational yield test -- may test separate groups of experimental lines; uses incomplete block design or triple lattice design with 2-3 replications in one location - preliminary yield test -- evaluation including a check variety using incomplete block design with 2-3 replications in at least 2 locations - general yield test -- uses randomized complete block design with 3 replications in at least 3 locations - advanced yield test -- elite lines from general yield tests evaluated using randomized complete block design with 4 replications in 6-10 locations - Superior lines are approved to be released as a variety by the National Seed Industry Council (NSIC); the variety must have passed the tests for distinctiveness (D), uniformity (U) and stability (S) or the DUS test. 4. **Seed --** seed or any other propagating material used for raising a crop **Seed multiplication involves:** a. **seed production** -- should observe proper isolation procedures to maintain genetic purity of the variety **Isolation** -- separation of a population of plants from other genotypes with which they are capable of mating - - b. **seed processing** -- drying , cleaning and grading, testing (purity, viability and moisture content determination), treating (disinfectants and protectants), bagging and labeling **Types of varieties:** - hybrids -- first generation offspring of a cross between two individuals differing in one or more genes - synthetics -- seed mixture of strains, clones, inbreds, or hybrids maintained by open-pollination for a specified number of generations; the component units are propagated and the synthetic reconstituted at regular intervals - composites -- mixture of genotypes from several sources, maintained by normal pollination - inbred -- a pureline originating by self-pollination and selection - multilines -- or blends; composite of isolines **Isolines** -- lines that are genetically similar except for one gene - open-pollinated variety -- variety maintained by natural cross pollination - landraces -- farmer-selected cultivated forms **Hybrid seed production** - 3-line system -- male sterile line (A), maintainer line (B) and restorer line (R) - 2-line system -- male sterile line, the expression of which is influenced by environment and any inbred variety as pollen parent - 1-line system -- use of apomixes to produce the F1 seeds and maintain the genotype of the F1 5. **Classes of seeds** - Breeder seeds: planting materials (seed or vegetative propagules) produced by or under direct control or supervision of the breeder (controlled by the originating plant breeder); starting point of all the subsequent classes of seeds; seeds obtained from uniform panicles by breeders; 100% pure; source of foundation seeds. - Foundation seeds (basic seed): seeds produced from breeder seeds and maintained according to required standards of the government; highest form of certified seeds in the commercial seed market, and produced in close supervision in an agricultural experimental station; source of registered and/or certified seeds; 98% pure with at least 85% germination rate; carry a red tag - Registered seeds (first generation seed): produced from foundation or breeder seeds and carry a green tag; must meet the quality standards set by certifying agency before they can be produced as source of certified seeds; sometimes omitted in the process. - Certified seeds (second generation seed): produced from foundation, registered or certified seeds and carry a blue tag; can be used for commercial production of crops but not for producing more certified seeds, instead, can be used for producing uncertified seeds or good seeds. - Good seeds: produced from varieties not yet approved by the National Seed Industry Council (previously Philippine Seed Board), but may meet standards set by other certifying agencies. 6. - primary centers -- where domestication occurred - secondary centers -- where variation continued after domestication **Germplasm storage** - as seeds in cold/refrigerated rooms - maintained as living plants in field or through slow growth in vitro - cryopreservation or freeze-preservation 7. **Domestication altered modern crop lines from its progenitor:** e.g. Teosinte (Zea mays ssp. mexicana) inflorescence has no cob allowing the seed to separate and dispersed easily when they mature, compared with modern corn (Zea mays ssp. mays L.) with types that retain seed on the ear leading to development of the cob. **Biotechnology:** (broad definition) refers to the use of living organisms or their components to provide useful products. e.g. making wine, beer, or bread; composting organic materials; releasing parasitic wasps to control insect pests; breeding plants or animals; and producing crops and livestock. 1. 2. 3. 4. 5. a. b. 6. a. 1. **DNA markers:** identify locations where the sequences differ among varieties or breeding lines. These can be locations within genes or in the DNA between genes, so long as they are unique sequences and differ between the plants of interest. Greater numbers of DNA-based markers can be identified to cover all regions of an organism's DNA, and they are not based on the developmental stage of the plant, as many protein based markers are. 2. **Protein markers:** based on differences in the proteins that are synthesized from the genes. Abundant proteins that are not enzymes, such as the seed storage proteins of cereal grains, can also be separated and stained to reveal specific size patterns characteristic of different genotypes. a. a. a. 7. - **Year 1996 to 2001:** global production area for transgenic crops (e.g. soybean, cotton, corn and canola) increased from 0 to 50 million hectares - **Calgene's Flavr Savr tomato:** first commercial food product derived from a transgenic crop variety; commercialized in year 1994 (presently no longer available in the market); Recombinant DNA and transformation techniques allow plant breeders to use genes from essentially any source as tools for crop improvement. - **Golden Rice:** accumulation of beta-carotene (which is converted into vitamin A when consumed by animals) in rice grains: scientists used genes from daffodil, pea, a bacterium, and a virus. Transgenic plant methods enable these four well characterized genes to be inserted into a transgenic plant, producing a highly specific change in only the trait of interest. - **Bt corn:** Corn that has been inserted with BT toxin gene from Bacillus thuringiensis bacteria in order for the corn to be poisonous to corn borer (with alkaline gut) but not to humans (with acidic stomach). b. c. -  References Sheaffer, C.C. & Moncada, K.M. (2012). Introduction to Agronomy: Food, Crops, and Environment, 2nd ed. Delmar, Cengage Learning, New York, USA. Acquaah, G. (2009). Horticulture, Principles and Practices, 4th ed. Pearson Education, Inc., New Jersey, USA Lantican, R.M.(2001)The Science and Practice of Crop production. SEARCA, Los Baños, Laguna, Philippines.