Soybean cultivars resulted from more recombination events than unselected lines in the same population

The selection of superior adapted cultivars has contributed to the doubling of soybean [Glycine max (L.) Merr.] yields in the USA since 1930. Genetic variation was required for this selection to be effective. The objective of this study was to evaluate the importance of homologous chromosome meiotic recombination in the creation of soybean cultivars. A set of 10 adapted high yielding cultivars selected from the cross 'Williams' x 'Essex' was compared with a set of 156 random recombinant inbred lines (RILs) from the same population. Crossover events were identified using 143 simple sequence repeat (SSR) markers spanning all 20 soybean chromosomes. The recombination rates were standardized among chromosomes by dividing the realized crossovers by the potential crossovers. The standardized recombination rate for the entire genome was significantly greater for the 10 cultivars (0.34) than for the RILs (0.29). The cultivars had numerically higher standardized recombination rates for 17 of the 20 chromosomes, significantly higher on chromosomes defined by the molecular linkage groups C2, L, and M. The interaction of linkage groups with the two sets of lines was nonsignificant for standardized recombination. Soybean breeding progress has been accomplished in part by creating and capitalizing on new within chromosome allele combinations.