Delving Into Stem Canker Disease of Potato Caused by Paramyrothecium roridum: A Morphological and Host Range Study in Iran

In the summer of 2019, a severe stem canker disease affected potato (Solanum tuberosum) plants in a 10-hectare commercial field in Kermanshah province, Iran. Approximately 10% of the plants exhibited wilting, leaf yellowing and brown stem lesions with black sporodochia. Infected plants produced small tubers with no visible lesions. Ten fungal isolates from diseased plants were identified as Paramyrothecium roridum based on colony culture, microscopic characteristics, and analysis of the internal transcribed spacer (ITS) region and part of the β-tubulin gene. The pathogenicity of P. roridum on seedlings was confirmed by fulfilling Koch’s postulates. Host range studies revealed a broad pathogenicity of the P. roridum isolate, successfully infecting various plant species with varying disease severities. Cucumis melo (melon) and Nicotiana rustica (wild tobacco) displayed susceptibility, while Triticum aestivum (wheat) and Avena sativa (oat) from the Poaceae family exhibited resistance. This study identifies P. roridum as a novel cause of potato stem canker disease in Iran.