Relationship between Soybean Sudden Death Syndrome Disease Measures and Yield Components in F6‐Derived Lines

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Soybean [Glycine max (L.) Merr.] sudden death syndrome (SDS), caused by Fusarium solani (Mart.) Sacc. f. sp. glycines Roy can cause substantial yield loss. To determine the relationship between SDS and yield components, 16 F6‐derived lines from the cross ‘Pyramid’ ✕ ‘Douglas’ were tested in two southern Illinois locations (Cora and Ridgway) with natural infestation by the SDS pathogen. Plots were rated for disease incidence (DI), disease severity (DS), and reproductive development stage (R). DI and DS were standardized to R6. Disease index (DX) was calculated as DI×DS/9. Individual plant data collected on three plants per 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 per pod, seed weight per plant, and 100‐seed weight. Seed quality was rated only at Ridgway. The among genotypes (genetic) covariance and the within genotype (environmental) covariance detected significant reductions in yield per unit of DS and DX (whole plot data). The genetic covariance with individual plant DS detected a significant reduction per unit of DS in total seed weight per plant. The environmental covariance with DS detected significant reductions in all yield components except flowers, empty pods, and seed per pod. There was a significant correlation of G✕E effects of most yield components and DS. Generally, genetic and environmental covariances were similar in magnitude and direction, suggesting that test genotypes were similar in the components affected and the degree of yield loss associated with a given level of disease.