First Report of the Telial Stage of Japanese Apple Rust on Juniperus chinensis in North America and the Aecial Stage on Malus domestica

Effects of Temperature, Moisture, and Ultraviolet Light on Germination, Infection, and Survival of Gymnosporangium yamadae Teliospores and Basidiospores

Apple rust caused by Gymnosporangium yamadae is a significant disease in China's main apple production areas. We evaluated the effects of temperature, moisture, and ultraviolet (UV) light on the germination, infection, and survival of teliospore horns and basidiospores under artificially controlled environmental conditions. The temperature required for the germination and infection of teliospores and basidiospores of G. yamadae ranged from 5 to 25°C, with an optimum temperature of approximately 17°C. The teliospore horns germinated after soaking in distilled water for 5 min and required at least 2.3 h of development to produce basidiospores under the most favorable conditions. The basidiospores germinated only in free water and produced germ tubes 0.8 h after being placed in the water. The half-life of the basidiospore was 72.5 h in the dark and only 9.5 h when exposed to intense UV light. The basidiospores inoculated on the host leaves required at least 2.3 h of water exposure to cause rust lesions. A revised Weibull model could describe the relationships between the germination and infection of teliospore horns and basidiospores with temperature and wetness duration. Collectively, these results can serve as a valuable guide for developing a model to predict future apple rust epidemics and establish a method for effective control strategies.