COMBINING ABILITY AND HETEROSIS ESTIMATES FOR KERNEL CADMIUM LEVEL IN SUNFLOWER

On certain soil series, nonoilseed sunflower (Helianthus annuus L.) yields kernels with a cadmium (Cd) concentration in excess of some international Cd limits. The purpose of this study was to determine the relative importance of general combining ability (GCA), specific combining ability (SCA), and heterosis estimates needed to develop low Cd hybrid cultivars of nonoilseed sunflower. The kernel Cd accumulation of 36 sunflower F-1 hybrids, obtained by crossing six inbred cytoplasmic male-sterile lines to six inbred male-fertile lines in a factorial mating design, was evaluated from held tests conducted at four locations with different soil types. Although the genotype x location interaction was statistically significant, the correlations for Cd among locations were significant over F-1 hybrids and parental lines, indicating that inbred parental Lines and hybrids performed consistently across the four locations. GCA was significant and accounted for 80% of the hybrid sums of squares. The interaction between males and females also was significant. These results indicate that additive genetic effects predominantly Influence the expression of kernel Cd accumulation in hybrids. The regression of actual hybrid kernel Cd on expected hybrid kernel Cd, based on parental GCA values, was highly significant. Although the regression of actual hybrid kernel Cd on midparent also was statistically significant, the R(2) value was only 0.21. These results indicated that GCA was more effective than midparent for describing hybrid performance. The levels of heterosis varied widely among crosses, ranging from -50 to 50%. Twenty-seven of the 36 crosses registered double-digit negative heterosis, indicating breeding for low kernel Cd in sunflower hybrids should be feasible.