Temperature and Leaf Wetness Effects on Infection of Sugarcane by Puccinia melanocephala

Brown rust epidemics in sugarcane, caused by Puccinia melanocephala, vary in severity between seasons. To improve the understanding of disease epidemiology, the effects of leaf wetness, temperature and their interaction on infection of sugarcane by the pathogen were studied under controlled conditions. Disease severity was low at 15 and 31°C regardless of leaf wetness duration. No infection occurred with a 4‐h leaf wetness period. Increasing leaf wetness duration from 7 to 13 h lowered the temperature required for disease onset from 21 to 17°C. More infection occurred with 13 compared to 10 h of leaf wetness at 17°C, and severity decreased for all leaf wetness periods at 29 compared to 27°C. Postinfection suboptimal low and high temperatures increased the time required for lesion development and high temperatures decreased maximum disease severity. The observed effects of leaf wetness and temperature on infection by P. melanocephala could help explain the initiation, rate of increase and decline of brown rust epidemics in the field.