Following EMS, DES and gamma ray treatment in Arkel and Bonneville pea varieties, three male sterile mutants were induced in Pisum sativum. Sterility in each of these is conditioned by single recessive genes, the three genes being non-allelic. Whereas in one mutant, the ms gene acts during pre-meiosis, in the other two the genes act during post-meiosis. In the premeiotic mutant, the PMCs either degenerate before attaining genetic autonomy or after separating out from one another. Their chromatin either compacts or fragments to degenerate completely. Thus, no meiosis occurs in this mutant.
In both the post-meiotic mutants, male meiosis is normal. In one, the microspores are released from the PMCs either in free or in adhered state. They develop thick walls, their chromatin condenses centrally and finally they degenerate. In the other mutant, monads are released from the PMCs. In 93% microspoes, the nuclear degeneration is faster than cytoplasmic degeneration, in 7% the reverse occurs. In both the post-meiotic mutants, microspores degenerate fully. Male sterility in all the three mutants is complete while female fertility is normal.