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

Step 1. East (1925) identified a self-incompatibility gene, S, in Nicotiana as an extended allelic series (S1, S2, S3...); cross-fertilising plants are always heterozygous for two different S alleles, never homozygous.

Step 2. Self-sterility means a plant's own pollen cannot fertilise its own ovules.

Step 3. The mechanism is allele matching: pollen carrying an S allele already present in the stigma's genotype fails to develop a functional pollen tube (always the case for self-pollination or identical S-genotype crosses like S1S2 x S1S2); pollen carrying a new S allele succeeds. …

Describe the S-gene allelic series and the allele-matching rule determining fertili …

• Describing self-incompatibility only generically without explaining the sp …