Submitted to: Soybean Research World Conference Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 8/5/1999
Publication Date: N/A
Technical Abstract: Mycelial compatibility and aggressiveness of Sclerotinia sclerotiorum isolates were assessed from a field set of 20 soybean isolates collected from a 725 m2 area and a geographically diverse set from various hosts. Isolates were identified as incompatible when paired isolates produced an interaction zone consisting of sparse mycelia, aerial mycelial, or a distinct red barrage zone. Relative aggressiveness of each isolate on soybean was assessed in a greenhouse study using a limited-term, plug inoculation technique and was reported as area under disease progress curve (AUDPC). Five mycelial compatibility groups (MCGs) were identified among the field set and 12 MCGs were identified among the geographically diverse set. Aggressiveness of isolates within both sets differed (P=0.05). In the field set, only two of 20 isolates were incompatible with all others, and the remaining isolates were grouped into three MCGs consisting of four, five, and nine isolates each. Aggressiveness of isolates in MCG-1 was higher (P=0.05) than isolates in MCG-2. Aggressiveness of isolates in the three remaining MCGs did not differ from isolates in MCG-1 or MCG-2. Ten of 18 isolates in the geographically diverse set were incompatible with all others, an the remaining eight isolates were grouped into two MCGs. S. sclerotiorum is a homothallic fungus with relatively high levels of genetic heterogeneity across hosts, geographic regions, and also within a field population. Mycelial incompatibility tends to perpetuate discrete genets that may be characterized by host specificity, geographic range, or aggressiveness. These data suggest that level of aggressiveness may be conserved within MCGs of a field population of isolates.