First Report of <i>Fusarium fujikuroi</i> Causing Leaf Blight of Potherb Mustard ( <i>Brassica juncea</i> var. <i>multiceps</i> ) in China

ABSTRACT Potherb mustard ( Brassica juncea var. multiceps , also known as multishoot mustard), a leafy vegetable crop of the Brassicaceae family, is predominantly cultivated in China's Zhejiang Province for post‐harvest processing. A previously unrecorded, severe foliar blight was observed affecting potherb mustard in Wencheng County, Zhejiang, during August 2024. The disease was characterized by the development of large, irregular necrotic lesions that initiated at the leaf margins, typically at the leaf tip or mid‐margin, and primarily affected the lower (older) leaves. These lesions exhibited a colour gradient from light beige to yellowish‐brown and caused the affected tissue to become desiccated, brittle and slightly distorted. A fungal pathogen was consistently isolated from diseased tissue. Based on congruent morphological features and a phylogenetic analysis of concatenated sequences from the ITS, RPB2 and TEF1‐α loci, the fungus was identified as Fusarium fujikuroi . Its pathogenic role was confirmed by satisfying all criteria of Koch's postulates. This study establishes the identification of F. fujikuroi as the causal agent of leaf blight on potherb mustard, representing its first report in China and highlighting a new threat to production.