Soybean Response to Sudden Death Syndrome: Inheritance Influenced by Cyst Nematode Resistance in Pyramid × Douglas Progenies

Abstract

To determine the inheritance of soybean [Glycine max (L.) Merr.J response to sudden death syndrome (SDS), 90 F6‐derived lines from the cross of ‘Pyramid’ × ‘Douglas’ were tested in field conditions in two replications of each of six southern Illinois environments naturally infested with the SDS pathogen Fusarium solani (Mart.) Appel & Wollenw. emend. Snyd. & Hans. Lines were rated for disease incidence (DI, 0–100%), disease severity (DS, 1–9), and the reproductive growth stage (R). The DI and DS were standardized to the full pod (R6) growth stage. Disease index was calculated as DI × DS/9, with a possible range of 0 (no disease) to 100 (all plants dead). Lines were also characterized in the greenhouse as resistant or susceptible to soybean cyst nematode (SCN; Heterodera glycines Ichinohe) Races 3 and 14. The group of SCN resistant lines was significantly less susceptible to SDS than the SCN susceptible group in three of the six environments. In Pulaski 1991, lines with SCN Race 3 and 14 resistance were significantly more susceptible to SDS on average than the SCN susceptible lines and than the lines with SCN Race 3 resistance only. Multigenic inheritance was implicated because the frequency distributions of SDS response were continuous with a large range (8–12 times the standard error of a line mean) in all environments and were unimodal in all but one environment. On the basis of line means, heritability estimates within environment ranged from 0.68 to 0.83 and across environments were 0.75, indicating that soybean response to SDS is highly heritable. There was a significant genotype × environment interaction in these lines emphasizing the need for multiple‐environment testing for effective selection of stable resistance to SDS.