Regeneration of soybean plants from embryogenic suspension cultures treated with toxic culture filtrate of Fusarium solani and screening of regenerants for resistance

Soybean embryogenic suspension cultures established from immature cotyledons of four cultivars were selected for resistance to a toxic culture filtrate of Fusarium solani, the causal agent of sudden death syndrome (SDS) of soybean. The embryogenic cultures were challenged with the fungal culture filtrates for 1 to 2 months. Many well-developed somatic embryos formed when the toxin-selected embryogenic cultures were incubated on regeneration medium; however, only a few plants were regenerated from three cultivars, whereas 98 plants were regenerated from cv. Jack embryos. The regenerants that survived were grown to maturity to obtain more seeds for screening plants for resistance to SDS. In the first experiment, the R₁ (187, first- selfed generation) and R₂ (225, second-selfed generation) plants of cv. Jack regenerants, resistant line P1520.733, and cvs. Jack, Great Lakes 3202, and Ripley were inoculated with a F. solani SDS isolate and rated on a 1 to 5 scale. The regenerants had significantly (P < 0.05) lower mean disease ratings than two of the three cultivars but did not differ from P1520.733. In the second experiment, R₃ plants (990 from cv. Jack and 53 from cv. Spencer) were screened for SDS resistance. The regenerants did not differ significantly from the other cultivars/lines in mean disease severity ratings, although a greater percentage of regenerants (Jack and Spencer R₃ combined) had disease severity ratings of 1 and 2 than did the soybean cultivars tested but not greater than P1520.733. The regenerants with lower disease severity ratings were grown to maturity to produce 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.