Cotton is an often cross pollinated crop. The percentage of cross pollination varies from 5 – 25% promoted by insects. The slight elevated position of the stigmatic surface leads to occasional cross pollination. In cotton, flowering starts from the base and proceeds towards the tip (i.e. acropetal and centrifuge). It takes 21-25 days for the flowers to open after the recognition of squares. The time of anthesis is between 8 and 10am. The flower will remain opened till evening. Pollen is shed directly on the stigma when the anthers open and hence self pollination is the rule. In cotton, the stigma is receptive for 7 hours while the pollen viability is upto 24 hours. Fertilization is completed in 36 to 40 hours after pollination.
Selfing
1. Selfing method
A mature flower bud is selected and the corolla is tied with a piece of thread. In order to keep the threads in position apply a bit of wet clay over the knot. This will avoid contamination of the stigmatic surface by foreign pollen. 2. Paper cover method
A small paper cover is put over the mature flower bud before anthesis and kept for 2-3 days.
Crossing
1. Doak’s method
A mature flower bud is selected from which the corolla is removed and total staminal column is peeled off by making a narrow cut at the lower portion of flower bud. Care should be taken not to injure the ovary. After the emasculation, cover the flowers with red paper covers. This is called Doak’s method.
2. Soda straw method
The upper part of the corolla is removed from the mature flower bud by making a circular cut at the top. Then a small piece of soda straw is inserted over the stigma, so that the stigmatic region is separated from the anthers. The tip of the straw is bent to close the opening. Next morning a few mature anthers collected from the male parent are crushed and dropped into the soda straw and cross pollination is effected.
Alternatively, well matured male flower is taken to the emasculated flower and anthers are wiped over the stigma. Pollens from one flower is sufficient to pollinate four emasculated flowers. After crossing, cover the flowers with white cover.
Cotton (Pollination Techniques) - Video Clip (Duration: 00.00min)
Self pollination is the rule in this crop in both Corchorus capsularis and Corchorus olitorius. The natural crossing in C. capsularis is higher rate and it is due to the wind pollination and insect visitation. Anthesis starts one to two hours after sunrise in C. capsularis and about an hour before sunrise in C. olitorius. The stamens usually burst before anthesis.
Selfing
To ensure self fertilisation, the flowers may be protected by covering them with fine mesh muslin bags or a polyethylene lantern. This is necessary in the c. capsularis species where cross pollination is much higher. The supports by bamboo stakes are given to bags which are covering the flowers, since the jute is a tall plant and inflorescence is at the top.
Crossing
Cross pollination between varieties within a species are readily made but the interspecific crosses are rarely successful. This is due to endosperm abortion. Emasculation is done one day ahead or at the time of opening of the flowers. Normally, the first bud to open in an inflorescence is emasculated and the other buds are removed. The most advanced bud in the inflorescence can be identified from its size and yellow colour of the petals and anthers. The buds selected is opened and the stamens are removed with fine pointed forceps. The emasculated flowers are covered with small butter paper bags to protect them from the dew and rain.
Pollination
Pollination is made following morning upto 9.30 AM incase of C. olitorius and upto around 11AM in case of C. capsularisThe stigma of the emasculated flower is lightly touched with a ripe anther and the pollen is dusted on the stigma. After pollination, the flowers are bagged for 24 hours. Seed capsules matured in about 6 weeks.
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