Spatiotemporal dynamics of Phytophthora infestans airborne inoculum in Belgium

Abstract For nearly a century, scientists have strived to model the development of Phytophthora infestans ( Pi ) to predict late blight infections in potatoes. This has led to the use of decision support systems (DSSs) that rely on forecasting models based on environmental parameters. All these models assume that the primary inoculum is ubiquitous. This study focuses on the spatiotemporal distribution of airborne inoculum of Pi to assess the value of incorporating quantitative data of this variable in improving the prediction of primary infection of potato late blight in fields. The daily spatiotemporal distribution of Pi airborne inoculum was studied from 2019 to 2022 at Ath, Gembloux, Libramont and Louvain-la-Neuve in Belgium by combining Burkard spore traps with a quantitative PCR assays. The quantities of Pi inoculum trapped daily ranged from 0 to 4903 (expressed as sporangia equivalent) depending on the site and the year. The appearance of late blight symptoms in untreated plots located close to spore traps was assessed shortly after the detection of airborne inoculum in all monitored sites. A comparison between airborne inoculum detection and the recommendations provided by three DSSs revealed that fungicide treatments are often recommended at the beginning of the season when airborne inoculum is absent. Two field trials performed in 2021 and 2022 showed that the number of fungicide treatments could be reduced by considering the presence of the inoculum, particularly by delaying the first application. Further knowledge of the relationships between disease pressure, airborne inoculum and meteorological conditions will provide valuable information for improving DSSs and reducing fungicide use.