Characterization of <i>Fusarium oxysporum</i> Species Complex Isolates Associated with Pea Fusarium Wilt in China

Pea (Pisum sativum L.) is a globally important legume crop cultivated for food or feed. Fusarium wilt, caused by Fusarium oxysporum f. sp. pisi (Fop), is a major constraint on pea production worldwide. Despite China being one of the leading pea producers, knowledge of pea Fusarium wilt and Fop remains relatively limited. In this study, the pea Fusarium wilt samples were collected from 10 provinces between 2015 and 2020 in China, and 79 pathogenic F. oxysporum isolates were obtained. Race identification using a standard differential set revealed that 49 isolates belonged to race 1, 5 to race 2, 16 to race 5, and 9 represented novel virulence types. Screening for 14 Secreted in Xylem (SIX) genes demonstrated that SIX14 was universally present, suggesting a potential role in pathogenicity, whereas other SIX genes occurred in variable combinations that were partially associated with race differentiation. Multi-locus phylogenetic analyses based on five conserved loci resolved the isolates into nine phylogenetic lineages, including five corresponding to known species (F. odoratissimum, F. cugenangense, F. curvatum, F. nirenbergiae, and F. fabacearum) and four potentially novel species. Morphological observations of representative isolates further supported phylogenetic distinctions, although this subtle variation requires additional examination for formal species delimitation. Host range tests revealed that several pea-derived isolates also infected chickpea, lentil, mung bean, faba bean, and common bean, underscoring their broad pathogenic potential within legumes. This study provides the first comprehensive characterization of pea Fusarium wilt pathogens in China, integrating race structure, effector gene distribution, phylogenetic relationships, and host range. The findings highlight the complexity of Fop populations and provide a foundation for improved disease management and resistance breeding.