Predicted Response to S1 Selection for Agronomic and Disease Resistance Traits in Two Sunflower Populations

Variances, heritabilities, genetic and phenotypic correlations, and predicted gains were computed for quantitative disease resistance and agronomic traits from pooled S1 family data of Gene Pool II and ND 761 Helianthus annuus L. populations. Broad-sense heritability estimates for all traits were significant in both populations. Observed genotypic correlation coefficients were larger than their corresponding estimates of phenotypic correlation coefficients. Significant positive genetic correlations between resistance to Alternaria blight and Septoria leaf spot; and non-significant genetic correlations between Sclerotinia wilt disease reaction and agronomic traits were observed in both populations. Resistance to Phoma black stem was not significantly correlated with resistance to other diseases or yield. Genetic correlations of yield/ ha with reaction to Alternaria blight and Septoria leaf spot diseases in Gene Pool II were negative and significant. There were significant positive genotypic correlations between yield/ha and other agronomic traits except days to flower. The genetic correlation between Septoria leaf spot and Sclerotinia wilt disease reactions was positive and significant in ND 761. However, resistance to four diseases in ND 761 was inherited independently of yield/ha. Yield/ha was positively significantly genetically correlated with head diameter, head weight, seeds per head and oil yield in ND 761. The Smith-Hazel index in both populations was efficient in improving predicted gains of resistance to all four diseases (Alterna ria leaf blight, Septoria leaf spot, Phoma and Sclerotinia wiIt) when selection was focused on Alternaria blight and Sclerotinia wiIt resistance simultaneously. This selection index was also effective for both populations in improving gain for agronomic traits (head weight, 200-seed weight, oil content and yield/ha) when selection was for oil percent and yield/ha simultaneously. Smith-Hazel and desired gain indices with simultaneous selection of Alternaria blight and Sclerotinia wilt resistance, oil percent and yield/ha are suggested for the improvement of multiple disease resistance and agronomic traits in Gene Pool 11 and ND 761, respectively. The restricted selection index and desired gain index were most efficient in controlling gains for restricted traits, plant height and days to flower.