COMBINING ABILITY AND HETEROSIS ESTIMATES FOR KERNEL CADMIUM LEVEL INSUNFLOWER

On certain soil series, nonoilseed sunflower (Helianthus annuus L.) yi elds kernels with a cadmium (Cd) concentration in excess of some inter national Cd limits. The purpose of this study was to determine the rel ative importance of general combining ability (GCA), specific combinin g ability (SCA), and heterosis estimates needed to develop low Cd hybr id cultivars of nonoilseed sunflower. The kernel Cd accumulation of 36 sunflower F-1 hybrids, obtained by crossing six inbred cytoplasmic ma le-sterile lines to six inbred male-fertile lines in a factorial matin g design, was evaluated from held tests conducted at four locations wi th 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 f our locations. GCA was significant and accounted for 80% of the hybrid sums of squares. The interaction between males and females also was s ignificant. These results indicate that additive genetic effects predo minantly 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 statistic ally significant, the R(2) value was only 0.21. These results indicate d that GCA was more effective than midparent for describing hybrid per formance. The levels of heterosis varied widely among crosses, ranging from -50 to 50%. Twenty-seven of the 36 crosses registered double-dig it negative heterosis, indicating breeding for low kernel Cd in sunflo wer hybrids should be feasible.