How is Nicotiana exhibit self-incompatibility? Explain its mechanism.

Explanation

Self-sterility means that the pollen from a plant is unable to germinate on its own stigma and will not be Style able to bring about fertilization in Pollen tube the ovules of the same plant. East (1925) observed multiple alleles in Ovary Nicotiana which are responsible for self-incompatibility or self-sterility.The gene for self-incompatibility can be designated as `S,` which has allelic series `S_1 ,S_2,S_3,S_4 and S_5`
The cross-fertilizing tobacco plants were not always homozygous as `S_1 S_2 ` or `S_2 S_2` but all plants were Female heterozygous as `S_1 S_2, S_3 S_4 and S_5 S_6` When crosses were made between different `S_1 S_2` plants, the pollen tube did not develop normally. But effective pollen tube development was observed when crossing was made with other than`S_1 S_2` When crosses were made between seed parents with `S_1 S_2` and pollen parents with `S_2 S_3`, two kinds of pollen tubes were distinguished. Pollen grains carrying `S_3` were capable of fertilization. Thus, from the cross ` S_1 S_2 X S_3 S_4` all the pollens were effective and four kinds of progeny resulted `S_1,S_3 ,S_1 , S_4, S_2 s_3 and S_2 S_4`