Effect of High Temperatures on the Growth and Disease Development of Erysiphe quercicola on Rubber Trees

Powdery mildew is a serious disease of the rubber tree (Hevea brasiliensis) worldwide. Temperature is the main climatic factor that influences the development of this disease. In this study, the effects of five high temperatures (30, 32, 34, 36, and 38 °C) at each of six exposure durations (0.5, 1, 3, 6, 12, and 24 h) were measured for the pathogen at 0, 3, 12, and 48 h post-inoculation (hpi), which represented four life stages of the fungus (conidia, conidial germination, infection, and hyphal growth). The results indicated that the germination, infection, and disease severity were reduced with increasing temperature and exposure duration. Temperature and exposure duration also significantly interacted to affect all life stages (p < 0.001). The relationships of the inhibition rate of conidial germination, infection, and disease severity with duration of exposure time (et) and high temperature (T) were described by logistic equations, with the percentage variance accounted for above 68%. Ungerminated conidia were found to be the most resistant to high temperature for E. quercicola from rubber tree, out of the four stages tested in this study. Only controlled-environmental experiments were conducted, and field studies are needed to enhance disease forecasting of rubber tree powdery mildew.