Population Studies in Predominantly Self-Pollinated Species. VII. Survival of a Male-Sterility Gene in Relation to Heterozygosis in Barley Populations.

ECENT studies on the population dynamics of several largely selfing species have shown that the restrictions often postulated to be imposed on the mode and extent of recombination and genetic variability by their breeding habit could be alleviated in several ways. Natural selection can regulate various factors controlling the rate of recombination (GRANT 1958) , or maintain through heterozygote advantage substantial amounts of heterozygosity ( JAIN and ALLARD 1960; ALLARD and HANSCHE 1964a). A rather low amount of outcrossing combined with selection favoring heterozygotes of the intensities such as those observed in barley and lima bean populations can result in a highly flexible recombinational system (ALLARD and HANSCHE 1964b). Alternatively, there are known several examples of species in which the breeding system has been adjusted by selection for higher degrees of outbreeding through such devices as male sterility (LEWIS and CROWE 1952, in Origanum), exsertion of stigma (BREESE 1959, in Nicotiana) and the need of tripping by insects (DRAYNER 1956, in Vicia) . Male sterility as a factor for increased outbreeding was apparently first discussed by MATHER (1940) in relation to the evolution of gynodioecy. That a similar role in an inbreeding species could be of even greater adaptive significance was shown by JAIN (1961) who, with the help of a simple model, demonstrated that a small proportion of male-sterile individuals having a higher rate of outcrossing than the population average permits higher levels of hybridity at equilibrium, or putting it otherwise, that the same levels of heterozygosity can he maintained with less intense selection. The present study was undertaken to determine whether male sterility has the postulated effect on heterozygosis in populations of barley in which a recessive gene (ms) for male sterility had been introduced to encourage recombination ( SUNESON 1945). This paper presents some data on the survival of the ms gene in relation to the levels of heterozygosity at some other loci.