Evaluating target spot (Corynespora cassiicola) resistance in soybean (Glycine max (L.) Merrill) in a controlled environment

Target spot, caused by the fungus Corynespora cassiicola, has been an increasing problem for soybean growers in the Mid-south and southeastern United States. With favorable environmental conditions, the disease causes premature defoliation and substantial yield losses; therefore, identifying resistant germplasm is critical. Herein, a rapid screening technique for target spot resistance was used to evaluate varieties for possible use in a breeding program. Fifteen soybean varieties, along with a known susceptible variety, were evaluated against isolate C. cassiicola LIM01. Two of the sixteen varieties were identified as resistant and nine were moderately suscep-tible. A subset of these was evaluated with three additional C. cassiicola isolates; these isolates differed in combinations of cassiicolin-encoding genes. The soybean varieties Bedford and Council were observed to be resistant to each of the C. cassiicola isolates tested in this study but need to be further validated in a field environment. Plant populations developed using these parent varieties could provide a foundation for QTL mapping of regions conferring resistance to target spot and identifying disease resistance mechanisms that can be transferred into elite soybean varieties through marker-assisted breeding.

Automated summary

This study used a rapid screening technique to evaluate the resistance of 15 soybean varieties against target spot caused by Corynespora cassiicola. Two resistant varieties were identified, and some varieties showed resistance against different isolates of C. cassiicola. These resistant varieties could be used for further research on the resistance mechanisms of target spot.