ENVIRONMENTAL REQUIREMENTS FOR SPORE GERMINATION IN THREE SUGARCANE LEAF PATHOGENS

THE outbreak of orange rust in Queensland in 2000 brought very significant financial hardship to the Queensland sugar industry. Accompanying this was increased interest in leaf diseases and the conditions favouring their development. Improvements in weather monitoring equipment have meant that if more information on pathogen requirements were obtained, it would be possible to predict when and where leaf diseases would occur. In this paper, spore germination requirements for Puccinia kuehnii (orange rust), Puccinia melanocephala (brown rust) and Mycovellosiella koepkei (yellow spot) are examined as a basis for further work relating these conditions to variation in climate in canegrowing districts. Optimum relative humidities for spore germination are 97% for P. kuehnii and free water for P. melanocepahala and M. koepkei. Differences in temperature requirements between the pathogens were also noted. Some of these differences are consistent with observed disease distribution in Queensland. Further research into other aspects of the disease cycle is required to fully explain observed disease occurrence.