RELATIONSHIP BETWEEN GENETIC-DISTANCE AMONG PARENTS AND GENETIC VARIANCE IN POPULATIONS OF SOYBEAN

A major goal of soybean [Glycine max (L.) Merr.] breeding is the devel opment and identification of high yielding transgressive segregants. P opulations that have greater genetic variation should, on average, hav e more transgressive segregants than populations with lesser variance. The goal of this research was to study whether the genetic distances between parents of crosses were predictive of which crosses have the g reatest genetic variance for yield and other agronomic traits. Genetic variance for seed yield, plant height and maturity date was estimated for three sets of populations in field tests. The first set included eight populations evaluated in 1989 and 1990, the second set included 21 populations evaluated in 1993 and a subset of 13 populations evalua ted in 1994, and the third set included 24 populations evaluated in 19 94 and a subset of 10 populations evaluated in 1995. The parents of th e crosses were evaluated with RFLP markers to estimate RFLP distances (RFD) and for coefficient of parentage (CP) which was subtracted from one to measure genealogical distances (GD). Both GD and RFD were signi ficantly (P < 0.05) correlated with genetic variance for plant height for the first set. There were no significant correlations between eith er genetic distance estimator and genetic variance for any trait in th e second set. In the third set, GD was significantly correlated with m aturity and plant height and RFD was significantly correlated with mat urity. Genetic variance for yield was adjusted for maturity with covar iance analysis. These adjustments reduced the estimates of yield varia nce and mostly reduced the correlations between yield variance and gen etic distance estimates. To further evaluate the predictive ability of GD and RFD, the populations in each set were subdivided into two grou ps, one with parents that had the greatest genetic distance and the ot her with the least distance based on GD or RFD. The average genetic va riance for yield of populations in the more distant group was greater than for the less distant group for the first and third set. These dif ferences were significant for the third set in both years for RPD. The se results indicate that although genetic distance can not accurately predict genetic variance of individual crosses, it can on average be u seful to identify groups of crosses that will produce populations with greater genetic variance.