First Report and Biological Characterization of Penicillium crustosum Causing Root Rot in Polygonatum kingianum (Yunnan, China)

Root rot is a major disease restricting the cultivation and production of Polygonatum kingianum Coll. et Hemsl. This study aimed to identify the causal agent and characterize its biological properties. Pathogens were isolated from diseased rhizomes showing typical symptoms, and their pathogenicity was confirmed through Koch’s postulates using both detached rhizome inoculation and field pot experiments with spore suspension irrigation, in which typical root rot symptoms were reproduced. Based on morphological characteristics and multi-locus phylogenetic analysis (ITS, CaM, RPB2, and TUB), the pathogen was identified as Penicillium crustosum. Biological characterization revealed that the optimal conditions for mycelial growth and sporulation were 25 °C and pH 8–9, with Czapek agar being the most suitable medium. Light conditions significantly influenced fungal development; continuous darkness (24 h) favored mycelial growth, while an alternating light/dark cycle (12 h/12 h) significantly enhanced sporulation. Furthermore, the pathogen exhibited the highest utilization efficiency for soluble starch as a carbon source and peptone or yeast extract as a nitrogen source. These physiological traits suggest a strong adaptive capacity of the pathogen to environmental conditions associated with host rhizomes, which may contribute to disease development under cultivation conditions. To our knowledge, this is the first report of P. crustosum causing root rot in P. kingianum. The findings provide a basis for accurate pathogen identification and improve current understanding of the biological characteristics of this pathogen, thereby supporting future studies on disease monitoring and management.