ABSTRACT
In the present study, onion plants were tested under controlled conditions for the development of a climate model based on the influence of temperature (10, 15, 20 and 25°C) and leaf wetness duration (6, 12, 24 and 48 hours) on the severity of onion downy mildew caused by Peronospora destructor. The relative density of lesions was influenced by temperature and leaf wetness duration (P <0.05). The disease was most severe at 15°C. Data underwent nonlinear regression analysis. Beta generalized function was used to adjust the data related to severity and temperature, while a logistic function was chosen to represent the effect of leaf wetness on the severity of onion downy mildew. The response surface obtained by the product of the two functions was expressed as SE = 0.1506 * (((x-8)0.0614) * ((30-x)0.1419)) * (0.71642/(1+0.56954 * exp (-0.04460*y))), where SE represents the value of the estimated severity (0.1); x, the temperature (°C); and y, the leaf wetness (in hours). This climate model should be validated under field conditions to benchmark its use as a computational system for the prediction of onion downy mildew.
Keywords
Allium cepa; Peronospora destructor; epidemiology; plant disease forecast
