RFLP genetic similarity estimates and coefficient of parentage as genetic variance predictors for soybean yield

RFLP genetic-similarity estimates (RFLP-GS) and coefficient of parentage (CP) have been used as measures of genetic similarity within crop species. However, practical application of these measures in plant breeding remains uncertain. This study was designed to probe the utility of RFLP-GS and CP in predicting genetic variance (GV) for seed yield among inbred soybean [Glycine max (L.) Merr.] lines. To achieve this goal, five single seed descent populations were studied, representing a range of RFLP-GS and CP between the parents from 57 to 75% and 0.06 to 0.5, respectively. The GV for yield was estimated for each population through field evaluation of 30 inbred lines per population, in two North Carolina field locations during 1994. Both RFLP-GS and CP correctly identified the population with the highest GV; however, CP predicted GV for yield more efficiently (r(CP.RFLP-GS) = 0.91*; r(CP.GV) = -0.81*; and r(RFLP-GS.GV) = -0.58). The GV was near zero when the CP between parents was larger than 0.27 or when RFLP-GS was larger than 75%. Neither genotype x environment interaction nor low field precision were factors for the lower predictive value of RFLP-GS. Expected gains from selection agreed partially with RFLP-GS results but closely matched CP and the actual fate of populations in a USDA breeding program. These results indicated that caution should be taken in an applied soybean breeding program when crossing parents with a relationship larger than half-sib or when the RFLP-GS is larger than 75% when yield improvement is the main breeding objective.