REGENERATION OF SOYBEAN PLANTS FROM EMBRYOGENIC SUSPENSION-CULTURES TREATED WITH TOXIC CULTURE FILTRATE OF FUSARIUM-SOLANI AND SCREENING OFREGENERANTS FOR RESISTANCE

Soybean embryogenic suspension cultures established from immature coty ledons of four cultivars were selected for resistance to a toxic cultu re filtrate of Fusarium solani, the causal agent of sudden death syndr ome (SDS) of soybean. The embryogenic cultures were challenged with th e fungal culture filtrates for 1 to 2 months. Many well-developed soma tic embryos formed when the toxin-selected embryogenic cultures were i ncubated on regeneration medium; however, only a few plants were regen erated from three cultivars, whereas 98 plants were regenerated from c v. Jack embryos. The regenerants that survived were grown to maturity to obtain more seeds for screening plants for resistance to SDS. In th e first experiment, the R(1) (187, first-selfed generation) and R(2) ( 225, second-selfed generation) plants of cv. jack regenerants, resista nt line PI520.733, and cvs. Jack, Great Lakes 3202, and Ripley were in oculated with a K solani SDS isolate and rated on a 1 to 5 scale. The regenerants had significantly (P < 0.05) lower mean disease ratings th an two of the three cultivars but did not differ from PI520.733, In th e second experiment, R(3) plants (990 from cv. Jack and 53 from cv. Sp encer) were screened for SDS resistance. The regenerants did not diffe r significantly from the other cultivars/lines in mean disease severit y ratings, although a greater percentage of regenerants (Jack and Spen cer R(3) combined) had disease severity ratings of 1 and 2 than did th e soybean cultivars tested but not greater than PI520.733. The regener ants with lower disease severity ratings were grown to maturity to pro duce more seeds that will be used to screen plants for SDS resistance and for crossing to determine how heritable and useful the resistance is in these regenerants.