Species of Fusarium and Neocosmospora associated with citrus branch diseases in China

Species of Fusarium and related fusarioid genera are widely distributed and commonly associated with diverse plant hosts, either as saprobes, endophytes, or pathogens. Although fusarioid fungi have been implicated in citrus diseases worldwide, their diversity and pathogenic potential on citrus in China remain poorly characterized. To investigate their species diversity, extensive field surveys were conducted in several citrus-producing regions of China between 2021 and 2024. Symptomatic tissues exhibiting dieback, necrosis, gummosis, canker, and wood decay were collected from twigs, branches, and trunks. Based on multi-locus phylogenetic analyses and morphological characteristics, 336 fusarioid isolates from eight provinces were assigned to six Fusarium species complexes and the genus Neocosmospora, comprising 21 known species (15 Fusarium spp. and six Neocosmospora spp.) and three novel species, namely F. gummosum, N. reticulatae and N. unshiu. Among the known species, 13 are reported from Citrus spp. for the first time, and two represent new records for China. Pathogenicity tests revealed that most fusarioid isolates were pathogenic to citrus branches, with N. unshiu and F. asiaticum being the most aggressive, inducing gummosis and cortex and xylem necrosis, consistent with symptoms observed in the field. Notably, N. unshiu was found to be the dominant pathogen causing citrus trunk canker in Hanzhong City, Shaanxi Province, where it is widely distributed and causes significant damage to citrus. To our knowledge, this study represents the first comprehensive investigation of fusarioid fungi associated with citrus branch diseases in China and provides a basis for future pathogen monitoring, disease prevention, and management strategies.