Survival of Sclerotinia sclerotia under fire

Abstract

A series of experiments was performed to determine the effectiveness of stubble burning and dry heat on reducing the viability of sclerotia of Sclerotinia sclerotiorum, the causal agent of Sclerotinia stem rot of canola. An intense fire in a uniformly dense triticale stubble led to the death of all sclerotia. However, in another burn with wheat stubble of varying densities, sclerotia survived well when the amount of stubble cover on the ground was 70% or less and sclerotial viability was only reduced when 90% or more of the surface was covered in stubble. Further experiments in dense rice straw showed that temperatures in a stubble fire are variable within a field and also within the rice stubble profile with lower temperatures under fallen stubble and among standing straw than on top of fallen straw. Most sclerotia (98.1 and 98.4%) survived temperatures under 93°C, ∼43% survived temperatures between 93 and 107°C, and very few (27.5 and 1.8%) survived temperatures above 121°C. These results were then verified in a 90s oven experiment where all sclerotia survived under 93°C, 70% survived between 93 and 107°C and none survived temperatures above 121°C. The ability of sclerotia to germinate myceliogenically and carpogenically was significantly reduced when exposed to oven temperatures between 93 and 107°C. These sclerotia also took longer to germinate myceliogenically but were earlier to germinate carpogenically than sclerotia in the control or sclerotia exposed to temperatures below 93°C. Size did not affect the ability of the sclerotia to survive a stubble fire. Burning of stubble does not appear to be an effective method of control of Sclerotinia stem rot in the field.