ABSTRACT
Multinucleate Rhizoctonia solani isolates were recovered from soybean fields from five locations at a range of latitudes from 33 to 46°N. Out of 143 multinucleate isolates recovered, 51 isolates were anastomosis group (AG)-1 (35.6%), 9 were AG-2-2 (6.2%), 40 were AG-4 (28%), and 15 were AG-5 (10.6%). The remaining 28 isolates (19.6%) failed to anastomose with any of the testers (AG-1, 2-2, 4, or 5). Among the four AGs, AG-1 was found mainly in the more southern latitudes in contrast to AG-2-2, which was found mostly in the more northern latitudes. AG-4 and AG-5 were distributed across all latitudes. Effects of temperature on growth, sclerotia production (range from 5 to 30°C with 5° increments), and saprophytic survival using infested straw (range from -10 to 30°C with 10° increments) were studied with representative isolates from AG-1, AG-2-2, AG-4, and AG-5 isolated from different locations. Results indicate differential effects of temperature on growth rate and sclerotia production among the isolates within each AG. Optimum temperature for growth rate of all isolates tested from the different AGs was between 25 and 30°C; whereas, for sclerotia production, it was 25°C. Isolates from AG-1 had the highest mean sclerotia production. Saprophytic survival of isolates from all AGs tested declined linearly over time and with decrease in temperature in the survival study. Saprophytic survival of all isolates irrespective of AG collected from the southernmost location was lower at low temperatures than that of isolates collected from higher latitudes. Our results suggest temperature dependent response among isolates within different AGs of R. solani.
