Effect of rice growth stage, temperature, relative humidity and wetness duration on infection of rice panicles by Villosiclava virens

Abstract

In controlled environments, the influence of rice growth stage, temperature, relative humidity and wetness duration on infection by Villosiclava virens (cause of rice false smut) was assessed by inoculating the rice cultivar ‘Yueyou938’ with a conidial suspension (2 × 106 spores) until run-off. Rice plants grown in vitro, were inoculated at a late stage of panicle development, and averaged 90 % diseased panicles which was a higher incidence compared with those inoculated at a mid-stage in panicle development (66.5 %). There were significant differences in the effects of temperature and wetness duration on disease incidence, which increased rapidly from 48 to 120 h at both 20 and 25 °C. The highest level of disease (92.9 %) was obtained at 25 °C and 95 % RH with 120 h of wetness. In another set of experiments, inoculated rice plants were incubated in a plant growth chamber at 25 °C and 95 % RH for a wetness period; of 120 h, and then subjected to different combinations of temperature and relative humidity to determine the effects of both factors on infection by V. virens. A higher temperature (28 °C) during incubation was found to induce a significantly higher disease incidence compared with a lower temperature (20 °C). Given a wetness period of at least 120 h, temperature was the primary factor affecting disease development during the 2 week period after that. Disease incidence was modeled as a function of both temperature and wetness duration using a modified version of the Weibull model. There was good agreement between observed and predicted values (R 2 = 0.951 and P = 0.0001). The model was used to construct a risk chart for estimating the potential for infection based on observed or forecast temperatures and wetness durations.