INFLUENCE OF TEMPERATURE ON SURVIVAL OF PRATYLENCHUS-PENETRANS AND OF MICROSCLEROTIA OF VERTICILLIUM-DAHLIAE IN SOIL

Survival of natural populations of Pratylenchus penetrans in field soil and of laboratory-produced microsclerotia of Verticillium dahliae introduced to soil was determined at various temperatures under controlled environmental conditions. The mortality (Y) with time (X) of both pathogens, was best described by an asymptotic model of the form Y = a - b(e(cX)). The time required to kill 50% and 90% of P. penetrans was calculated from the curves obtained for all temperatures between 38 and 42-degrees-C. Thermal death curves for V. dahliae microsclerotia were obtained at 30, 35, 37, 40, 42, and 45-degrees-C under three moisture regimes and in soils from solarized and nonsolarized field plots. Microsclerotia were consistently killed more rapidly at all temperatures in the presence of high moisture regimes. When related to the mortality of both organisms observed under solarization conditions, the thermal death curves developed at constant temperatures tended to overestimate population demise of P. penetrans, whereas the predictions for V. dahliae were much more accurate.