Non-random mating in a Secale cereale L. (rye) population

Abstract

The mating system in an experimental population of rye (Secale cereale L.) cv. Merced was studied using eight polymorphic isozyme loci as genetic markers and two progeny samples from a large population: 20 emasculated mother plants (obligately cross-pollinating) and 100 non-emasculated mother plants. Merced rye showed a significant frequency of self-fertilization (s = 1 – t) in a previous generation, but in the generation under study the outcrossing frequency was not significantly different from t=1. This fact suggests that environmental factors can affect the rate of outcrossing vs. selfing (self-fertilization). In spite of the outcrossing rate of t = 1, the large progenies from emasculated plants (100 seeds per plant) demonstrated that pollination was not completely at random. This represents a violation of the generally accepted mixed-mating model on which most methods used to estimate mating parameters are based. Temporal heterogeneity and the differential ability of gametophytes to fertilize are possible causes of the non-randomness of mating. It is concluded that, although violations of the assumption of the mixed-mating model can bias the estimates, most of the estimated outcrossing values clearly differ from complete outcrossing.