Objective 1
Exp 1: We found that application of the ethylene inducer ethephon as a soil drench was effective at reducing SDS foliar symptoms compared to the water control, in greenhouse conditions. In contrast, MCP and cobalt chloride treatments did not significantly affect SDS severity. Treatment with ethephon did not affect Fv populations in soil, indicating that the suppression of SDS is not mediated by a direct effect on the pathogen.

Exp 2: Seedlings treated with ethephon (4mM) showed up-regulation of all defense-related genes tested (PR1, PR2, PR3, PR10, and chalcon synthase), compared to cobalt chloride or water treated seedlings, at all time points. This increase of expression of defense genes is the likely cause of SDS suppression after ethephon application. Cobalt chloride did not affect expression of defense related genes.

Objective 2.
Exp 3: All ethephon rates tested caused a reduction in SDS foliar disease severity compared to the water treated control, independently of time of application, but the higher rates caused a significantly greater reduction in SDS. For this reason, the rate of 4mM was used for field experiments.
Field experiment: At the Hinds farm location, ethephon applications at planting and at emergence reduced SDS severity and incidence compared to the water-treated plants. Foliar applications at V2 did not affect SDS. The impact on yield was not significant but there was a numerical trend for higher yield in plots treated with ethephon at planting. Results at the other two locations were inconclusive due to low disease pressure.
Triple response tests: the assay tested was not sensitive enough to detect differences in sensitivity to ethylene among soybean genotypes. A new approach will be tested in the next funding year.