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.( Modes of Pollination )
1) Autogamy or self pollination and
2) Allogamy or cross pollination.
Autogamy, or self pollination, is the transfer of pollen grains from the anther to the stigma of the same flower. The closest type of inbreeding is autogamy. Homozygozity is the result of autogamy. These animals achieve homozygous equilibrium and show no signs of inbreeding depression.(Modes of Pollination)
Mechanism promoting self-pollination
Bisexuality refers to the presence of male and female parts in the same flower. Self-pollination requires the existence of bisexual blooms. Hermaphrodite blooms are found on all self-pollinated plants. (Modes of Pollination)
Homogamy is the simultaneous maturation of a flower’s anthers and stigma. In most cases, homogamy is required for self-pollination.
Cleistogamy occurs when pollination and fertilisation occur in an unopened flower bud. Self-pollination is ensured, and cross-pollination is avoided. Cleistogamy has been seen in wheat, barley, oats, and a variety of other grass species.
Chasmogamy is defined as the opening of flowers only after pollination is complete. Wheat, barley, rice, and oats all contain this, which encourages self-pollination.
5. Position of Anthers
Self-pollination is assured in some species because stigmas are encircled by anthers. Tomato and brinjal are examples of this. The stamens and stigma are surrounded by the petals in certain legumes, allowing for self pollination. Greengram, blackgram, soybean, chickpea, and pea are some examples. (Modes of Pollination)
Allogamy, or cross pollination, is the transfer of pollen grains from one plant’s anther to another plant’s stigma. Outbreeding in this kind is the most prevalent. Heterozygosity is the result of allogamy. On selfing, these animals develop heterozygous balance and show substantial inbreeding depression. Cross pollination is aided by a mechanism. ( Modes of Pollination )
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.
Male and female flowers are found in the same inflorescence in several crops, such as mango, castor, and banana. In certain situations, like as in maize, they are on different inflorescences. Cucurbits, grapes, strawberries, cassava, and rubber are among more examples. Dioecy refers to the presence of staminate and pistillate blooms on distinct plants. Papaya, date palm, spinach, hemp, and asparagus are among the ingredients. (Modes of Pollination)
2. Dichogamy (from the Greek dikho-apart and gamous-marriage)
It describes when the anthers and stigma of the same flower mature at separate periods.
Even in hermaphrodite species, dichogamy encourages cross pollination. Dichogamy is of two types: viz.
i) protogyny and
Protogyny occurs when the pistil matures before the anthers, as in pearl millet. Protandry occurs when anthers develop before the pistil. It may be found in maize, sugarbeet, and a variety of other plants. ( Modes of Pollination )
Heterostyly refers to a flower’s styles and filaments being of various lengths. Linseed, for example, benefits from cross pollination.
Herkogamy is defined as a physical barrier against self-pollination, such as the presence of a hyline membrane around the anther. Such a barrier hinders pollen dehiscence and self-pollination in plants such as alfalfa. ( Modes of Pollination )
5. Self incompatibility
Self incompatibility is the inability of viable pollens to fertilise the same flower. It enhances cross pollination and inhibits self-pollination. Several crop species, such as Brassica, Radish, Nicotiana, and numerous grass species, have self-incompatibility. There are two forms of sporophytic algae: sporophytic and gametophytic.
Pollen grains are non-functional in some species. Male sterility is the term for this disorder. It enhances cross pollination and inhibits self-pollination. Genetic, cytoplasmic, and cytoplasmic genetic are the three categories. In hybrid seed development, it’s a valuable tool. Floral biology and the aforementioned mechanisms must be studied in order to determine the manner of pollination of distinct crop species.
Furthermore, if selfing has a negative impact on seed set and overall vigour, the species is cross pollinated. If selfing has no negative impact on these traits, it’s likely that the species is self-pollinated. Growing a seed combination of two distinct types together can be used to measure the percentage of cross pollination. Green and pigmented plants should be distinguishable between the two types. The seeds from the recessive (green) variety are gathered and planted in a different field the following year. Outcrossing or cross pollination will be shown by the percentage of pigmented plants in the green variety.
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
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.
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