Assistant Professor/Extension Specialist University of Wisconsin-Madison Madison, Wisconsin, United States
Abstract Text: Chondrostereum purpureum, the causal agent of silver leaf disease, is a wood decay fungus that infects apple (Malus domestica) and other woody hosts, leading to leaf silvering, branch dieback, and reduced tree vigor. Despite its impact on orchard health, its infection dynamics in apple trees under field conditions remain understudied, as it is thought to be most active during cooler periods. To assess its pathogenicity, a field inoculation experiment was conducted during the 2023–2024 season. Apple tree branches (cv. Cortland) were inoculated from November to April with two C. purpureum isolates, R167 and HHB-15295-SP, and one Diplodia seriata, a canker pathogen of apple, using a 5 mm plug method, with uninoculated controls included. Inoculated sites were wrapped and monitored, and branches were collected two months post-inoculation for lesion measurement and fungal re-isolation. Statistical analysis from the first season revealed significant differences in lesion development among isolates (p < 0.0001), with R167 causing the largest lesions, followed by HHB-15295-SP. Diplodia seriata did not produce lesions significantly different from the control (p = 0.5080). A replication of this experiment is underway for the 2024–2025 season, replacing D. seriata with a third C. purpureumisolate while retaining the two previously tested isolates and a control. This study provides insights into C. purpureumpathogenicity in orchard systems, contributing to a better understanding of its seasonal infection dynamics and potential management strategies.
