Development of a weather-based forecasting model for Alternaria leaf blight of carrot

ABSTRACT In the present study, under controlled conditions, the influence of temperature (10, 15, 20, 25 and 30°C) and leaf wetness duration (6, 12, 24 and 48 hours) was studied on the severity of Alternaria leaf blight of carrot caused by Alternaria dauci. The relative density of lesions was influenced by temperature and leaf wetness duration (P<0.05). The disease was more severe at the temperature of 25°C. Data underwent non-linear regression analysis. The generalized beta function was used for fitting the data on disease severity and temperature, while a logistic function was chosen to represent the effect of leaf wetness duration on the severity of leaf blight. The response surface resulting of the product of the two functions was expressed as ES = 0.004993 * (((x-8)1.13125) * ((36-x)0.53212)) * (0.39219/(1+25.93072 * exp (-0.16704*y))), where: ES represents the estimated severity value (0.1); x, temperature (ºC) and y, leaf wetness duration (hours). This model must be validated under field conditions to be used as a forecasting model for Alternaria leaf blight of carrot.