Analysis of Cytoplasmic Diversity in an Outcrossing Population of Soybean

Abstract

The maintenance of genetic variation is a critical consideration in the derivation of plant populations for use in recurrent selection or cultivar development. This study~was conducted to determine the number of distinct cytoplasmic genotypes contributed by female parents of a soybean [Glycine max, (L.) Merr.] population and the effect of continuous cycles of forced outcrossing on the maintenance of this cytoplasmic variability. 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 plants. Restriction fragment length polymorphisms (RFLPs) were used to assess chloroplast DNA (cpDNA) and mitochondrial DNA (mtDNA) variation. The 39 female lines were classified into six cytoplasmic groups based on cpDNA and mtDNA RFLPs. The combinations of cpDNA and mtDNA polymorphisms observed in these lines suggest a possible maternal lineage of G. max. Analysis of randomly sampled individuals from the population after one, three, five, and seven cycles of outcrossing revealed a gradual loss of cytoplasmic diversity in the population. Four of the six cytoplasmic groups were observed among 199 individuals sampled from the population after one outcrossing cycle, while only two of these cytoplasmic groups remained among the 135 individuals sampled from Cycle 7. The lack of reproductive success among plants with four of the six cytoplasmic genotypes has consequently reduced the cytoplasmic variability in this outcrossing population.