RELATIONSHIP BETWEEN SOYBEAN SUDDEN-DEATH SYNDROME DISEASE MEASURES AND YIELD COMPONENTS IN F-6-DERIVED LINES

Soybean [Glycine max (L.) Merr.] sudden death syndrome (SDS), caused b y Fusarium solani (Mart.) Sacc. f. sp. glycines Roy can cause substant ial yield loss. To determine the relationship between SDS and yield co mponents, 16 F-6-derived lines from the cross 'Pyramid' x 'Douglas' we re tested in two southern Illinois locations (Cora and Ridgway) with n atural infestation by the SDS pathogen. Plots were rated for disease i ncidence (DI), disease severity (DS), and reproductive development sta ge (R). DI and DS were standardized to R6. Disease index (DX) was calc ulated as DI x DS/9. Individual plant data collected on three plants p er plot were DS, total flowers, total pods at R5.5 (mid-pod-fill) and R8, total empty and partially filled pods at R8, total seeds, seeds pe r pod, seed weight per plant, and 100-seed weight. Seed quality was ra ted only at Ridgway. The among genotypes (genetic) covariance and the within genotype (environmental) covariance detected significant reduct ions in yield per unit of DS and DX (whole plot data). The genetic cov ariance with individual plant IDS detected a significant reduction per unit of DS in total seed weight per plant. The environmental covarian ce with DS detected significant reductions in all yield components exc ept flowers, empty pods, and seed per pod. There was a significant cor relation of G x E effects of most yield components and DS. Generally, genetic and environmental covariances were similar in magnitude and di rection, suggesting that test genotypes were similar in the components affected and the degree of yield loss associated with a given level o f disease.