Maintenance of male sterility in plant populations

Summary

Two models of monogenic recessive male sterility are presented, first where the male-steriles are always fully pollinated (full-fitness model) and second where they are only pollinated to the extent that hermaphrodites are crossed (limited-fitness model). Male-steriles in both models may be maintained by overdominance at the sex-control locus or by having greater ovule or seed fertility than hermaphrodites. For both models fitness of male-steriles is frequency dependent under random mating or under mixed selfing and random mating, and for the case when male-steriles are maintained only by increased fertility, expressions are derived for their equilibrium proportions and those of both hermaphrodite genotypes. Also for this latter case, fitness of male-steriles in equilibrium populations equals that of the hermaphrodites. In the full-fitness model the degree of selfing among hermaphrodites has little effect on equilibrium proportions of male-steriles, which may decline slowly, increase slowly, or remain constant with increased selfing. Except under random mating, equilibrium proportions of male-steriles are lower in the limited-fitness model and decline with increased selfing among hermaphrodites. Outcrossing rates for pollen of hermaphrodites are derived.