NONRANDOM MATING IN A SECALE-CEREALE L (RYE) POPULATION

The mating system in an experimental population of rye (Secale cerenle L.) cv. Merced was studied using eight polymorphic isozyme loci as ge netic,markers and two progeny samples from a large population: 20 emas culated mother plants (obligately cross-pollinating) and 100 non-emasc ulated mother plants. Merced rye showed a significant frequency of sel f-fertilization (s = 1-t) in a previous generation, but in the generat ion under study the outcrossing frequency was not significantly differ ent from t = 1. This fact suggests that environmental factors can affe ct 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 co mpletely at random. This represents a violation of the generally accep ted mixed-mating model on which most methods used to estimate mating p arameters are based. Temporal heterogeneity and the differential abili ty of gametophytes to fertilize are possible causes of the non-randomn ess of mating. It is concluded that, although violations of the assump tion of the mixed-mating model can bias the estimates, most of the est imated outcrossing values clearly differ from complete outcrossing.