Molecular Identification and Characterization of Fusarium Associated with Walnut Branch Blight Disease in China

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In October 2020, samples of walnut branch blight were collected from Longnan. Pathogens were isolated and identified based on morphological and molecular features, and their characteristics were analyzed by pathogenicity. Pathogenicity testing revealed that seven strains (LN-1, LN-3, LN-6, LN-19, LN-27, QY3-1, and QY9-1) induced symptoms of walnut branch blight that were consistent with those observed in the field after inoculation. Furthermore, some Fusarium-type conidia and spherical chlamydospores were visible indicating that they were Fusarium spp. A molecular characterization including sequence and phylogenetic analysis of the ITS, TEF-1α, βTUB, Fu, and LSU gene regions revealed that LN-1 and LN-19 belonged to F. avenaceum, LN-3 and LN-6 to F. acuminatum, LN-27 to F. sporotrichioides, and QY3-1 and QY9-1 to F. tricinctum. This is the first time that F. acuminatum-, F. sporotrichioides-, and F. tricinctum-caused walnut branch blight has been reported in China.