Pollination, Fertilization, Pollinizer and Pollinator
The transfer of pollen grains from the anther to the stigma is called pollination. Pollination is done by various means such as wind (anemophily), water (hydrophily), insects (entomophily), and animals (zoophily).
Pollen grains germinate on the stigma and the thin pollen tube grows through the style and enters the embryo sac, where the fusion of male and female gametes occurs which is called fertilization.
Mod of pollination
- Self-pollination – The transfer of pollen grains from the anther to the stigma of the same flower is called “self-pollination”.
- In autogamy, pollen grains of the same flower pollinate the stigma of the same flower.
- Geitenogamy is another form of self-pollination when pollination occurs between two flowers of the same plant.
- Cross-pollination – The transfer of pollen grains of one plant to the flower of another plant is called cross-pollination. The resulting fertilization is known as cross-fertilization or allogamy. For example, Castor, Niger, etc.
Crops have developed various mechanisms in the course of their development to ensure either self-pollination or cross-pollination.
Mechanisms favoring self-pollination:
Male and female reproductive organs are present in the same flower. Like, hibiscus, etc.
Here the anther and stigma of a bisexual flower mature at the same time. Green peas, etc.
Flowers do not open at all or open after pollination. Bisexual flowers ensure self-pollination such as lettuce, legumes, etc.
d) Flower structure:
In lady’s finger, the young pistil grows from the middle of a staminal tube, from which pollen falls on the associated stigma, leads to self-pollination.
Mechanisms to encourage cross-pollination
a) Imperfect Flowers:
Flowers are unisexual i.e. stamens and pistils are located on separate flowers.
- Monoecious plants: eg jackfruit, coconut.
- Dioecious plants: eg, papaya, asparagus, dates, etc.
Uneven maturation of stamens and pistils in bisexual flowers (the anther and stigma of bisexual flowers mature at different times). They are of two types:
- Protogyny: The stigma becomes first receptive to stamens. eg. Millet.
- Protandry: Breaks the anther and releases the pollen grains before the stigma of the same flower becomes receptive. For example, carrots, marigolds.
The presence of a mechanical barrier between the male and female organs of a flower. Like, crepes.
d) Male Sterility:
Seeds are not formed due to the absence of functional pollen grains or Male sterility is a condition in which pollen is absent and non- functional. Male sterility is determined by (i) genetic factors (eg tomato, barley, brinjal, and rice), (ii) cytoplasmic factors (eg, onion), and (iii) interaction (eg chili, etc.).
Male and female gametes are fertile, but selfing does not produce seeds due to some oppositional factors but can set seeds when cross-pollinated. For example, tobacco, mango, tomato, mustard, radish, cabbage, etc.
Classification of crops according to pollination
A) Natural or commonly self-pollinated crops
These crops have a high degree of self-pollination (>95%) and cross-pollination is less than 5%. Such as beans, chickpeas, groundnuts, sesame, and tobacco.
B) Naturally or normally cross-pollinated crops
Cross-pollination occurs mainly (>95%) in these crops with very little (ie, 5%) self-pollination.
- fruit crops like almonds, apples, bananas, cherries, chestnuts, citrus, dates, grapes, figs, papayas, mangoes, etc.)
- Vegetables are like all cruciferous crops.
C) Often cross-pollinated crops
These crops are generally self-pollinated. However, due to various agencies, the cross-pollination in these crops is usually more than five percent. For example, jowar, cotton, safflower, etc.
Pollinizers are plants that act as a source of pollen for successful pollination and fertilization. Some plants are capable of self-pollination, but the term is often used in pollination management to refer to a plant that provides abundant, compatible, and viable pollen at the same flowering time as the pollinated plant. For example, most Crabs apple varieties are good pollinizers for any apple variety that blooms at the same time and are often used in apple orchards for that purpose.
Conditions necessary for satisfactory cross-pollination
- The flowering period of the pollen and the main variety should be the same.
- The pollen variety should have viable diploid pollen.
- It can provide enough compatible pollen for the main variety
- The pollen variety should be located near the producing tree.
- Bees and other insects must be present in the garden and active during flowering.
Pollinators are organisms or agencies that carry pollen from the stamens to the stigma, such as wind, insects, birds, bats, or sometimes other animals.
Transfer of Pollen
- Insect Pollination (Entomophily): – Pollen grains are carried from one flower to another by house fly, honey bees, wasps, etc. By these, the process of pollination is done in mango, apple, plum, cauliflower, etc. The pollination method can also be called the entomophily mode of pollination.
- Bird Pollination (Ornithophily): – Birds, parrots also work to transfer pollen grains and this pollination is done in begonia, coral trees, etc. These are called ornithophily mode of pollination.
- Animal Pollination (Zoophily):- Some flowers are pollinated by mammals like monkeys, elephants, squirrels, it is called the zoophily mode of pollination.
- Bat pollination (Chiropterophily): – When pollination is done by bats, it is called chiropterophily mode of pollination like Anthocephalus cadamba, Kigellia pinnata.
- Wind Pollination (Anemophily):- Most of the fruit trees like date palm, coconut, papaya, pomegranate, etc. are pollinated by wind.
- Water Pollination (Hydrophily): – Pollination in lotus and some aquatic plants is done by water.