Bud pollination to overcome self-incompatibility is accomplished by opening the bud and transferring pollen from an open flower of the same plant. Fertilization will not occur where this is done when the bud is very small. At this stage, the style is not receptive, but about 3-4 days before the flower has opened the style and stigma are fully receptive and the self-incompatibility factor has not yet developed, therefore self-fertilization is possible and self-incompatibility can be bypassed.
The bud is opened with a pointed object, such as a mounted needle, and pollen transferred from an open flower. In some large breeding programmes, many, even hundreds, of pollinators can be used to produce selfed seed on self-incompatible plants.
There are two other methods now widely used to overcome the self-incompatibility. The first involves spraying 3-4% sodium chloride solution on to the open flower. It is then left for 20-30 min, the excess salt solution is removed by blowing it off the flower or blotting with a damp cloth or paper towel, and then self-pollination can occur. The salt removes the inhibitor from the stigma, permitting self-pollination. A second and more efficient method if many plants are involved is to self-pollinate the open flowers, and then place the plants in a closed unit or room into which 5% carbon dioxide can be admitted. Then the self-incompatibility factor is overcome and this allows the production of seed following self-pollination. Single plants can be self-pollinated and the flowers enclosed in a plastic bag; it is inflated by exhaling into it, using a straw, and then finally closed. This may be repeated again later in the day. The effect is similar to enclosing the plant in a room and adding carbon dioxide.
When the only method of production of hybrids was by the use of self-incompatibility, then self-fertile plants were usually discarded. Now with the interest in male sterility, the self-fertile plants are the desired ones and the self-incompatible plants are discarded. It is equally important, however, to establish that the plants are homozygous for self-compatibility and not just setting seed because they are heterozygous for SI genes.
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