Table 1_Macro-scale risk assessment and host response to orange rust (Puccinia kuehnii) in sugarcane across tropical zones under current and future climate scenarios.docx

Puccinia kuehnii, the causal agent of orange rust, is an obligate biotrophic fungus and an emerging phytosanitary threat to sugarcane production. Although widely distributed in Colombia, its current impact and future risk under climate change remain poorly understood. This study evaluated the present and potential future risk of orange rust in sugarcane systems dedicated to sugar and panela production in Colombia. A total of 252 disease occurrence records were collected from nine sugarcane-producing departments, and disease impact was assessed in commercial fields using a damage index across different sugarcane varieties. Spatial kernel analyses were used to characterize the distribution of disease damage, and the Kruskal-Wallis test was applied to compare severity among varieties. In parallel, ecological niche modeling was used to estimate the current and future potential distribution of P. kuehnii under climate change scenarios. Orange rust was detected in all sampled regions, with reaction scores above 5 and severity values reaching 50%. The highest disease intensity was recorded in Santander and Caquetá, particularly in varieties RD 75-11 and CC 93-7510, while variety CC 01-1940 also showed marked severity in the Cauca River Valley. The ecological niche models identified areas of high current environmental suitability and projected an expansion of favorable conditions into additional sugarcane-producing regions under future climate scenarios. Our findings show that orange rust poses a substantial current and future risk to Colombian sugarcane systems and provide a multiscale spatial framework to support surveillance, varietal management, and evidence-based decision-making for the sugarcane sector.