Factors influencing the airborne sporangia concentration of Phytophthora infestans and its relationship with potato disease severity

Abstract

Forecasting systems are widely used to predict the application of fungicides for managing late blight. However, airborne inoculum has rarely been included in these forecasting systems. Monitoring the sporangia in crop environments may offer an opportunity to improve late blight forecast systems by integrating pathogen pressure. Hence, this experiment aiming to analyze relationships between weather based risk systems and sporangia levels in the atmosphere of potato crops. The experiments were conducted during two growing seasons in a potato field. During the study, the concentration of Phytophthora infestans in the air, the weather conditions, the phenology of cultivars and r-AUPDC during the crop cycle were recorded. The weather-based risk of late blight was estimated using infection pressure (IP) and the daily risk value (DRV) based on hourly relative humidity (RH) and temperature (T). The effect of weather parameters on sporangia levels was analyzed. IP and DRV showed a strong positive correlation with sporangia concentration, standing out the pronounced effect of RH on the sporangia levels. Analysis of the hourly sporangia concentration within a day showed an increase in the sporangia concentration from 9 h to 18 h. This increase in sporangia was linked to an increase in T, spore release, and a decrease in RH. Our results identified a T of 10 ◦C and RH of 80% as the minimum threshold for significant sporangia concentration in the air. However, maximum sporangia level was found in the air at 88% (average relative humidity) and 17 ◦C (average temperature). Finally, the effect of weekly P. infestans sporangia was observed on cultivars with different susceptibility to late blight.