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The following points highlight the top ten methods to overcome incompatibility. The methods are: 1. Mixed Pollination 2. Bud Pollination 3. Styler Pollination 4. Intraovarian Pollination 5. Test tube Pollination 6. Treatment of Style with Heat 7. Irradiation 8. Treatment with Chemicals 9. Use of CO2 10. Parasexual Hybridization.
Method # 1. Mixed Pollination:
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In this technique the stigma is pollinated with incompatible and chemically treated compatible pollen. Chemicals which do not disturb the wall-held proteins are used. In this method the proteins leaching from the compatible pollen mask the inhibition reaction to be caused by the incompatible pollen, at the surface of the stigma.
There is also a suggestion that recognition pollen may also supply growth substances to cause germination of incompatible pollen. Using this method self-incompatibility has been overcome in Populus, Petunia, Cosmos, etc.
Method # 2. Bud Pollination:
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In a large number of plant species like Petunia, Brasicca, self-incompatibility could be overcome when self-pollination was done a few days before anthesis. In the bud stage the stigma does not produce exudate or the incompatibility reaction appears just before anthesis.
Method # 3. Styler Pollination:
In several species of Nicotiana, the site of incompatibility is the stigma surface. Thus when the stigma lobes are cut off and cut surface of the style is dusted with self-pollen, the pollen tubes grow through the style uninhibited. Some-times agar sucrose is smeared on the cut surface and made into an artificial stigma.
Method # 4. Intraovarian Pollination:
In this technique a known amount of pollen and basal medium are injected in the ovary with the help of a hypodermic syringe. Seeds are successfully obtained following proper fertilization.
Method # 5. Test tube Pollination:
In this method the pollen grains and ovules are cultured side by side in the nutrient medium and the technique is excellent for employing placental pollinations e.g., in Petunia.
Method # 6. Treatment of Style with Heat:
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In Liliuml self-incompatibility is suppressed when the styles are subjected to a temperature of 50-C for five minutes.
Method # 7. Irradiation:
In some instances incompatibility genes have been mutated through the use of irradiation. For instance, Lycopersicon peruvianum self-incompatible clones were given gamma radiations treatments and the seed set was obtained.
Method # 8. Treatment with Chemicals:
Several chemicals like 2-4, D, kinetin, chlorophenoxyacetic acid, etc. have been used to overcome incompatibility.
Method # 9. Use of CO2:
In Brassica sp. like B. campestris, B. oleracea following self-pollination when the carpels were enclosed with high concentrations of CO2 (3-5%) there was good amount of seed set. Malik, Dhaliwal and Singh have provided a working model that CO2 was fixed non- photosynthetically to produce malate. It also stimulates pentose phosphate shunt, which was a source of reducing power (NADPH). Malate acted as an osmoregulatory solute.
Method # 10. Parasexual Hybridization:
In this approach the protoplasts from desirous genotypes were isolated enzymatically and fused under controlled conditions. The culturing of these protoplasts were affected and the whole plants could be raised in some plant species.
