Chapter 4 Plant Reproductive Systems 1 3 Plant
- Slides: 42
Chapter 4. Plant Reproductive Systems 1
3. Plant Reproductive System 1) Type of plant life cycles and their implication in breeding 2) Basic types of floral morphology 3) Mechanisms of pollination and fertilization 4) Breeding implications of self- and cross-pollination 5) Constraints to pollination and their implication in breeding 6) Genetics and applications of male sterility in breeding 2
Importance of mode of reproduction to plant breeding Why breeders need to understand the mode of plant reproduction? Key reasons…. 1. The genetic structure of plants depends on their mode of reproduction 2. Artificial hybridization is needed to conduct genetic studies to understand the inheritance of trait of interest, and for transfer of genes of interest from one parent to another 3
Importance of mode of reproduction to plant breeding Why breeders need to understand the mode of plant reproduction? Key reasons…. 3. Artificial hybridization requires an effective control of pollination so that only the desired pollen is allowed to be involved in the cross 4. The mode of reproduction determines the procedures for multiplication and maintenance of cultivars developed by plant breeder 4
Overview of reproductive options in plant 1. Hermaphrodity versus unisexuality 2. Self-pollination versus cross-pollination 3. Self-fertilization versus cross-fertilization 4. Sexuality versus asexuality 5
Overview of reproductive options in plant 1. Hermaphrodity versus unisexuality Hermaphrodity: have both male and female sexual organs -> self-fertilization is possible -> promote a reduction in genetic variability 6
Overview of reproductive options in plant 1. Hermaphrodity versus unisexuality Unsexuality: have one kind of sexual organs -> cross-fertilization is possible -> promote genetic variability 7
Overview of reproductive options in plant 2. Self-pollination versus cross-pollination Self-pollination Cross-pollination 8
Sexual reproduction of flowering plant Sexual life cycle = alteration of generation Two basic growth phases of flowering plant 1) Vegetative phase: plant produces vegetative growth only 2) Reproductive phase: plant produces flowers The process of sexual reproduction 1) Meiosis: 2 n (diploid) -> n (haploid) = gametophyte generation phase 1) Fertilization: n (gamete) + n (gamete) -> 2 n (zygote) = sporophyte generation phase 9
Alternation of generation in flowering plants 10
Sexual reproduction of flowering plant Duration of plant growth cycles 1) 2) 3) 4) Annuals Biennials Perennials Monocarps Types of flower 1) 2) 3) 4) Complete flower (e. g. , soybean, tomato, cotton, tobacco) Incomplete flower (rice, wheat, corn) Perfect flower (=bisexual, wheat, tomato, pepper) Imperfect flower (staminate or pistilate flowers, cucumber) 11
Four life cycles of flowering plant 12
Sexual reproduction of flowering plant Types of flower 5) Monoecious plant (staminate and pistilate flower on the same plant, corn) 6) Dioecious plant (staminate and pistilate flower on the different plant, papya, asparagus) Gametogenesis In gametogenesis, gametes(n) are produced from specialized diploid cells called microspore mother cells in anthers and megaspore mother cells in the ovary to be united and transformed into an embryo 13
Four basic part of the typical flower 다양한 화기 구조 1. 완전화 (complete flower)와 불완전화 (incomplete flower) 2. 양성화(perfect flower)와 단성화(imperfect flower) 3. 자화(pistilate flower)와 웅화 (staminate flower) 4. 자웅동주 (monoecious plant)와 자웅이주 (dioecious plant) 5. 단화(solitary flower)와 화서(inflorescence) 14
Gametogenesis in Plant 15
Sexual reproduction of flowering plant Pollination & Fertilization 1) Pollination: the transfer of pollen grains from the anther to the stigma of a flower 2) Fertilization: one of the sperms unites with the egg cell, and the other sperm cell unites with the two polar nuclei (triple fusion) = double fertilization Self-pollination Mechanism that promote self-pollination : 1) Cleistrogamy; the condition that the flowers open only after it has been pollinated (wheat, barley, lettuce) 16
Sexual reproduction of flowering plant Self-pollination Genetic & breeding implication of self-pollination: 1) achieves a highest degree of inbreeding 2) promotes homozygosity of all gene loci and traits = the genotypes of gametes of a single plant are all the same 3) the progeny of a single plant is homogeneous 4) restricts the creation of new gene combination 5) Mutations are readily exposed through homozygosity 6) Specific breeding methods: pure-line selction, pedigree breeding, bulk population, and backcross breeding 17
Sexual reproduction of flowering plant Cross-pollination Mechanism that promote cross-pollination : 1) Dioecy: a plant is either female or male but not hermaphrodite 2) Monoecy: receive pollen from their own male flowers 3) Dichogamy; in hermaphroditic flowers, the stamens mature before the pistil is mature and receptive (protandry) or the reverse (protogyny) 4) Self-incompatibility; the pollen from a flower is not tolerated by its own stigma 5) Male sterility; the pollen of male is sterile 6) Heterostyly; significant difference in the lengths of the stamen and pistil 18
Sexual reproduction of flowering plant Cross-pollination Genetic & breeding implication of self-pollination: 1) Genotype of the sporophytic generation is heterozygous 2) Genotypes of gametes of a single plant are all different 3) New gene combinations are created in the next generation 4) When selfed, ‘Inbreeding depression’ occurs 5) Hybrid vigor is exploited in hybrid seed production 6) Usually population-based breeding methods; mass selection, reccurrent selection, synthetic cultivars 19
Asexual reproduction Vegetative propagation Vegetative = bulbs, corms, rhizomes, stems, buds Mechanism that promote cross-pollination : 1) Flowering and fertility is reduced 2) Numerous plantlets are generated from small piece if vegetative materials by using cutting, grafting, micropropagation (tissue culture) 3) potato, yam, cassava, sugarcane, and many fruit trees 20
Asexual reproduction Vegetative propagation Genetic & breeding implication of vegetative propagation 1) Once a desirable genotype combination has been achieved, clonal cultivas can be released immediately following the cross. 2) Heterosis is fixed (maintained indefinitely) in the hybrid product 3) Clonal crops are perennial outcrossers and intolerant of inbreeding 4) General combining ability (GCA) and specific combining ability (SCA) can be fully exploited with appropriate breeding methods and population size 21
Apomixis Ability to develop seed without fertilization Apomictically produced seeds are clones of the mother plant = apomixis is the asexual production of seed Found from 10% of 400 plant families (Gramineae, Compositae, Rosaeae, and Asteraceae) and 1% of 40, 000 species (citrus, brerries, mango, perennial forage grasses) Facultative apomixis: produce both sexual and apomitic seed Obligate apomixis: produce only apomitic seeds 22
Apomixis Indicators of apomitics 1) Indicator of facultative apomitics: the progeny from a cross in a cross-pollinated species fails to segregate 2) Indicator of obligate apomitics: multiple floral feature, multiple seedlings per seed, the progeny of a cross shows a high number of identical homozygous individuals that resemble the mother plant in addition to the presence of individuals that are clearly different 23
Apomixis Benefits of apomixis: 1) A breeding tool to develop hybrids that can retain their original genetic properties indefinitely with repeated use 2) Breeders can use this tool to fix superior gene combination 3) No need to maintain and increase parental genotypes 4) No need for producers to purchase fresh hybrid seed each year 24
Apomixis Mechanisms of apomixis 1) Apospory 2) Diplospory 3) Adventitious embryo 4) Parthenogenesis 25
Constraints of sexual biology in plant breeding Some constraints are exploited as hybrid breeding tool Methods for controlling cross-pollination(crossing) 1) Mechanical control: removing anthers from bisexual flowers to prevent pollination (emasculation) 2) Chemical control; chemical hybridizing agents (gametocides, male steriliants, pollenocides, androcides) 3) Genetic control; male sterility, self-incompetibility 26
Onion flower…. . How would you cross-pollinate this plant? 27
Constraints of sexual biology in plant breeding Self-incompatibility =>a condition in which the pollen from a flower is not receptive on the stigma of the same flower and hence is incapable of setting seed 1) Heteromorphic incompatibility (Heterostyly) 2) Homomorphic incompatibility a) Gametophytic incompatibility; the ability of the pollen to function is determined by its own genotype and not the plant that produces it b) Sporophytic incompatibility; the incompatibility characteristics of pollen are determined by the plant that produce it 28
이형예 현상(Heterostyly) Genotype Ss ss 1. ss x ss = 불임 (sterile) 2. Ss x Ss = 불임 (sterile) 3. ss x Ss = 임 (fertile) 4. Ss x ss = 임 (fertile) 29
자가 불화합성 (Self-incompatibility) 1) 배우자 불화합성 (Gametophytic incompatibility) 가) 나) 다) 라) pollen의 genotype에 의해 임성/불임성이 결정 pollen은 haploid이며 dominance가 성립치 않음 S allele에 대한 heterozygote만 형성 됨 Style 내에서 pollen tube의 생장이 저해 됨 2) 아포체 불화합성 (Sporophytic incompatibility) 가) Pollen을 생성하는 sporophyte의 genotype에 의해 임성/불임성이 결정 나) Sporophyte은 diploid로서 dominance 관계가 성립 다) S allele에 대한 homozygote도 형성될 수 있음 라) Stigma 상에서 pollen tube 성장이 저해 됨 30
Application of selfincompatibility in practical plant breeding 31
Constraints of sexual biology in plant breeding Male sterility =>a condition in plants whereby the anther or pollen are nonfunction 1) Genetic (nuclear, genic) male sterility 2) Cytoplasmic (mitocondrial gene) male sterility 3) Cytoplasmic-genic sterility 32
Male sterility observed in the anther of rice flower fertile sterile Pollens Anther 33
Constraints of sexual biology in plant breeding Genetic Male sterility controlled by a single recessive nuclear gene, ms genetically male-sterile types => msms A pure population of genetic male-sterile plants can not be produced Male-sterile genes may be carried along at a high frequency in a self-pollinate crop if seeds from the male -sterile plants only are harvested and used to plant next generation 34
Genetic male sterility as used in practical breeding 35
Constraints of sexual biology in plant breeding Cytoplasmic Male sterility (CMS) Controlled by cytoplasm (mitochondrial gene) A cytoplasm without sterility gene = normal (N) cytoplasm A cytoplasm that cause male sterility = a sterile (s) cytoplasm or said to have cytoplasmic male sterility (CMS) CMS is transmitted through the egg (female plant= maternal factor) Fertility is restored by dominant fertility-restoring genes transmitted through the pollen gametes The pollen parent may have either CMS or normal cytoplasm 36
Maize tassel phenotype Fertile male flowers Sterile male flowers 37
Onion flower phenotype Fertile anther Sterile anther 38
Cytoplasmic male sterility 39
Constraints of sexual biology in plant breeding Cytoplasmic-genetic Male sterility (CMS) Fertility is restored by dominant fertility-restoring genes transmitted through the pollen gametes The pollen parent may have either CMS or normal cytoplasm Utilization in a breeding program 1) Eliminate emasculation in hybridization 2) Increase natural cross-pollination in self-pollinated crops 3) Facilitate commercial hybrid seed production 40
The three systems of cytoplasmic male sterility: The teree factors involved in CMS are the normal cytoplasm, the male-sterile cytoplasm, and the fertility restorer (Rf, rf) 41
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