Chloroplast DNA evidence for non-random selection of females in an outcrossed population of soybeans [Glycine max (L.)].

Restriction fragment length polymorphisms (RFLPs) were used to assess chloroplast DNA (cpDNA) variation in a population of soybeans subjected to continuous cycles of forced outcrossing. This population was derived by crossing 39 female lines with four male-sterile (Ms2ms2) maintainer lines and advancing each generation by selecting only outcrossed seed borne on male-sterile (ms2ms2) plants. Analysis of the original 39 female lines revealed three groups based on cpDNA RFLPs. These three groups had been previously documented in soybeans, and the distribution of these groups among the female parents of this population was similar to that observed in germ plasm surveys of soybean. Thirty-four of the female parents had group I cpDNA, 3 had group II, and 2 had group III. Plants collected from this population after seven cycles of outcrossing were scored for four morphological traits (flower color, pubescence color, seed color, and pubescence type) known to be controlled by alleles at single nuclear loci. The frequencies of the phenotypes observed in this study indicated that the population underwent random mating with respect to flower and pubescence color, but deviated from random mating at the other two loci. Analysis of 158 of these same plants collected from the population after seven cycles of outcrossing revealed no individuals with group II or group III cpDNAs. The fixation of the group I cpDNA marker in this outcrossing population was judged to result primarily from selection against individuals in the population with the rare cpDNAs.