Genetic distance as a predictor of heterosis and hybrid performance within and between heterotic groups in sunflower

Heterosis is significant for seed yield and is one of the driving forces behind the hybrid seed industry in cultivated sunflower (Helianthus annuus L). Heterotic groups in sunflower, if any other than the female and male inbred-line groups exist, have not been well studied or described. The primary aims of this study were to assess the utility and validity of a series of proposed heterotic groups and estimate correlations between genetic distance, heterosis, and hybrid performance for seed yield in sunflower. Fortytwo female by male heterotic group (A x R) and 81 female by female heterotic group (A x B) single-cross hybrids were grown in Corvallis, Ore., and Casselton, N.D., in 1996 and 1997. Heterosis was significant for seed yield and plant height but not for seed oil concentration and days to flowering. Genetic distances were significantly correlated with hybrid seed yield when estimated from AFLP fingerprints (G(D),) (r = 0.63 for A x R and 0.79 for A x B hybrids), but not from coancestries (Gc) (r = -0.02 for A x R and 0.54 for A x B hybrids). G(D), (R-2 = 0.4) was a poor predictor of hybrid seed yield. The proposed heterotic groups in sunflower seem to have utility, but do not seem to be as strongly differentiated as those in corn (Zea mays L.). The highest-yielding hybrids were from the B-C X R-B, heterotic pattern; however, several B-C X B-C, hybrids (within-group hybrids) were among the top-yielding hybrids. The outstanding performance of certain B-C X B-C, hybrids casts some doubt on the validity of the B-C group. Substantial genetic diversity seems to be present within and between heterotic groups in sunflower.