SOYBEAN RESPONSE TO SUDDEN-DEATH SYNDROME - INHERITANCE INFLUENCED BYCYST-NEMATODE RESISTANCE IN PYRAMID X DOUGLAS PROGENIES

To determine the inheritance of soybean [Glycine mar (L.) Merr.] respo nse to sudden death syndrome (SDS), 90 Fs-derived lines from the cross of'Pyramid' x 'Douglas' were tested in field conditions in two replic ations of each of six southern Illinois environments naturally infeste d with the SDS pathogen Fusarium solani (Mart.) Appel & Wollenw. emend . Snyd. & Hans. Lines were rated for disease incidence (DI, 0-100%), d isease severity CDS, 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 x DS/9, with a possible range of 0 (no dis ease) to 100 (all plants dead). Lines were also characterized in the g reenhouse as resistant or susceptible to soybean cyst nematode (SCN; H eterodera glycines Ichinohe) Races 3 and 14. The group of SCN resistan t Lines was significantly less susceptible to SDS than the SCN suscept ible group in three of the six environments. In Pulaski 1991, lines wi th 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 bec ause the frequency distributions of SDS response were continuous with a large range (8-12 times the standard error of a line mean) in all en vironments 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 x environment interaction in these lines emphasizing the need for mul tiple environment testing for effective selection of stable resistance to SDS.