Determining agro-climatic favourability zones for coffee leaf rust in Brazil – a new approach for assisting crop risk planning

Coffee leaf rust (CLR) poses a significant threat to coffee crops worldwide, including those grown in Brazil. CLR thrives in climatic conditions ideal for coffee cultivation, which results in its constant presence in Brazilian coffee farms. The intensity of CLR exhibits variations as affected by interannual and spatial climate variability that shape epidemics. The aim of this study was to determine the agro-climatic favourability zones for CLR occurrence in the major coffee-producing regions of Brazil based on region-specific agro-climatic conditions. Climate data spanning from 1961 to 2015 at 46 sites were selected to represent the major coffee-producing regions. Using a CLR infection rate model, daily simulations were performed to calculate the cumulative infection rate (CIR) for each site and growing season, starting from 1^st October to 30^th June of the following year. Based on the CIR values, the sites and seasons were categorised into five favourability classes: Very Low, Low, Medium, High, and Very High. An Agro-Climatic Favourability index (ACFav_index) was developed, considering the frequency of seasons falling within each favourability class. A map displaying four distinct favourability zones across the studied regions was then obtained and showed that most of the traditional coffee-growing areas fell within the Medium to High Favourability zones for CLR. The obtained map, delineating CLR favourability zones, holds practical value for coffee growers, consultants, and policymakers alike. It can guide the selection of CLR-resistant coffee cultivars for new cultivation areas and aid in the development of effective disease control strategies.