The Effect of Temperature and Nematode Species On Interactions Between the Nematophagous Fungus Verticillium Chlamydosporium and Root-Knot Nematodes (Meloidogyne Spp.)

Optimal growth and sporulation on agar of an isolate of Verticillium chlamydosporium occurred at 32-degrees-C and 22-degrees-C, respectively. Differences in the numbers of colony-forming units isolated from the root surface of tomato plants grown at different temperatures reflected the rate of hyphal growth on agar. However, the numbers of colony-forming units in soil at different temperatures was related to the effect of temperature on sporulation in vitro; the fungus was most abundant in soil at 22-degrees-C, which was the optimal temperature for sporulation. After one nematode generation the most extensive root colonisation occurred at 20-degrees-C followed by 25 and 30-degrees-C. As a result, egg-masses exposed on the root surface were most extensively colonised at 20-degrees-C followed by 25 and 30-degrees-C. Total egg and juvenile counts showed that greatest control of Meloidogyne was achieved at 25-degrees-C (c 90%), while control at 20 and 30-degrees-C was usually 60-70%. The lower level of control by V. chlamydosporium at 20-degrees-C may result from a reduced proportion of nematode egg-masses exposed on the root surface at this temperature. Eggs of M. arenaria, M. incognita and M. javanica were equally susceptible to parasitism by V. chlamydosporium. Of these three species, M. arenaria induced large galls and formed large egg-masses while M. incognita and M. javanica induced small galls and formed small egg-masses at 20-degrees-C. The end result was that control with V. chlamydosporium was approximately the same for the three nematode species.