Many summer residents when choosing planting material in the description of a particular plant variety meet mention of various methods of pollination or self-pollination. These are the concepts that we all studied back in school at the lessons of botany. But not many already remember what they mean. Let's refresh our memory and recall the types of pollination in plants and their biological significance. And at the same time we will find out why some of our plants planted in the country house or on the windowsill do not give fruit.
Generative organ of higher plants
A flower is a modified shoot where spores and gametes are formed. Higher plants (angiosperms) have complex flowers with many adaptations to various types of pollination. A flower that is diverse in its details combines the processes of both sexual and asexual reproduction. The main components of the flower are its reproductive parts - the male androecium (stamens) and the female gynoecium (pistil with ovary, column and stigmas). Flowers can be bisexual (there is both a pistil and stamens) and same-sex (there is either a pistil or stamens). The other components of the flower are very diverse and perform specific functions.
The meeting of stamens and pestle
Pollination is the process of transferring pollen from stamens to the stigma of a pestle. Without this, it is impossible to propagate plants, the formation of fruits and seeds. In the process of evolutionary development, plants have developed several ways to carry out this transfer using biotic and abiotic factors of nature. In ecology, two types of pollination are distinguished:
- Transfer pollen from one flower to the pistil of another. This process is called cross-pollination, or xenogamy. It is carried out through biotic (insects, birds, bats) and abiotic (wind, water) factors.
- Autogamy (self-pollination). This is the transfer of pollen on the stigma from one flower. Autogamy is not so common in wild forms.
These are types of pollination that can alternate in some plants.
Self Pollination Conditions
But a prerequisite for the implementation of self-pollination is the bisexuality of the flower. Random self-pollination of flowers is a common event. But it can occur only with the physiological compatibility of pollen grains and pestles. In many plants, pollen does not grow into a pollen tube, which is a limiter for cross-pollinated plants. There are many factors that contribute to random autogamy. Regular self-pollination of plants (for example, peas, beans) can have a gravitational mechanism. In this case, pollen falls on the stigma under the influence of gravity. In other cases, self-pollination occurs as contact autogamy - the stamen comes into contact with the stigma of the pestle. Dewdrops and small insects (thrips) that live in the flower can act as carriers of pollen in the middle of the flower. In some plants, the process occurs in the bud and completely eliminates the possibility of cross-pollination.
Optional self-pollination
A feature of this type of autogamy is the presence of unstable conditions that do not favor cross-pollination. This type of self-pollination is found in cereals, sundews, feather grass. In these plants, under drought or at low temperatures, unisexual flowers form, and in warm and humid weather, bisexual flowers. Cross-pollination of these plants is carried out with the help of wind, and in conditions of difficulty in the implementation of such pollination it is biologically advisable to resort to self-pollination.
Evolutionary significance
Self-pollination in the evolutionary sense is negative. In accordance with modern concepts, evolution requires free crossbreeding, which is ensured by cross-pollination. It is it that increases the diversity of alleles (degrees of gene manifestation) in populations. And self-pollination, on the contrary, leads to homozygosity (uniformity) of alleles. But under certain circumstances, self-pollination can lead to the isolation of new forms, isolation and fixation in the population of alleles that give favorable signs to the plant. It is precisely in this that the positive evolutionary significance of the alternation of autogamy and xenogamy lies.
Self-pollinating plants
In such plants, pollen transfer is often carried out even in an unopened bud (for example, in beans and peas) or in the period of an unopened leaf tube (barley). Self-pollinators from crops are peas, beans, barley, wheat, oats, tomatoes, eggplant and many others. Why count? Because self-pollination cannot be absolute, there is always the possibility of pollen being introduced from other plants. Even closed buds sometimes gnaw at insects and carry pollen from other plants! What signs distinguish self-pollinators? This is definitely a plant with bisexual flowers, large cirrus stigmas and lots of pollen. In addition, their flowers do not have bright petals, nectaries and a pleasant smell.
Self-pollination in violets
In nature, violets are pollinated both crosswise and autogamously. Our indoor violets are the product of the painstaking work of breeders. They have such a structure of stamens and pestle that cross-pollination without human intervention is almost impossible. Pollination takes place even in an unopened bud, and only a patient amateur with the help of special techniques can pollinate violets of different colors to produce new varieties. Thanks to the enthusiasts for the variety of these colors that adorn our windowsills!
Parthenocarpic cucumbers
Modern selection offers many varieties of cucumbers, both self-pollinated (parthenocarpic) and pollinated by insects. These plants are bred specifically for early growing in greenhouses where there are no natural pollinators. When buying seeds, you need to stop reading the qualities of the variety, since self-pollinated and cross-pollinated varieties have their advantages and disadvantages.
Pollination in cereals
Oats, rye, wheat, millet, barley - representatives of agricultural cereals. Flowers have 2 flower scales, 2 films, three stamens and one pistil. Self-pollination in them occurs in undisclosed flowers. When the flower has opened, cross-pollination is virtually eliminated.
Self-pollination in fruit trees
Although most fruit varieties have flowers in which there are pistils and stamens, self-fertilization is excluded in most. The reason is the timed maturation of the stamens and pestle. That is why it is possible to increase the yield, for example, cherries, by planting several trees nearby. But in artificially bred varieties, self-pollination is welcome. An example is nectarines. But do not hope to grow a fruitful plant from the seed. In such hybrid forms, subsequent generations experience hybrid depression - a decrease in vitality and productivity.
Selection and self-pollination
This phenomenon is widely used in plant breeding. We know that self-fertilization and crossbreeding of closely related organisms leads to the transition of genes into a homozygous state and leads to a decrease in vitality and productivity, and subsequently degeneration. The continuous process of mutations that accumulate, most of which are recessive and unfavorable, is the cause of this oppression. In plants with cross-pollination, these mutations are in a heterozygous state and do not appear in any way. With self-pollination, the probability of their transition to homozygous increases many times, but they are not preserved in the population due to natural elimination. Self-pollination in breeding is used as a tool for creating clean (homozygous) lines with fixed attributes. Despite the decrease in productivity, the phenomenon of heterosis often appears after hybridization - the strength of hybrids from cultivars with self-pollination. This phenomenon is called interline hybridization, and in stores we can see exactly such hybrid seeds (they are marked with the F1 symbol). In the first generation, hybrids outperform clean lines in yield, but in future generations the effect of the strength of hybrids disappears.