Effect of soil moisture at different temperatures on Rhizoctonia root rot of wheat seedlings

The effect of soil moisture at different temperatures on root rot of wheat seedlings caused by Rhizoctonia solani AG-8 was studied in temperature controlled water tanks under glasshouse conditions. Four moisture levels (15, 30, 50 and 75% of soil water holding capacity at saturation which were equal to -10, -7, -5 and -3 kPa, respectively) were tested in tanks maintained 10, 15, 20 or 25 degreesC. The role of microbial activity in the effect of soil moisture and temperature on disease severity was also studied by including treatments of steam treated soil. Results showed that at soil moisture levels optimum for plant growth (50 and 75% WHC) disease was more severe at a lower temperature (10 degreesC), but under relatively dry conditions (15% WHC) disease levels were similar at all temperatures tested. In warm soils (20 and 25 degreesC) at high soil moisture levels (50 and 75% WHC), disease was more severe in steam treated soil than in non-steam treated soil, indicating that the suppression of disease in natural soil under these conditions was associated with high soil microbial activity.