Evaluation of pathogenicity, host resistance, biological properties and chemical control of <i>Xanthomonas fragariae</i> Strain JD1 causing angular leaf spot on strawberry

Angular leaf spot (ALS), caused by the quarantine pathogen <i>Xanthomonas fragariae</i>, is a major bacterial disease threatening global strawberry production. In China, its continued spread across multiple regions poses a significant and persistent epidemiological threat to the strawberry industry. Recently, ALS has emerged as a great threat to strawberry industry in the Jiande, Zhejiang province (located at 29°N, 119°E). This study reports the first isolation and characterization of X. fragariae strain JD1 from symptomatic strawberry leaves in Jiande, Zhejiang Province. The identification of strain JD1 was confirmed through species-specific PCR, analysis of colony characteristics, and phylogenetic clustering based on 16S rRNA and HrpB gene sequences. Pathogenicity assays revealed strain JD1 resulted in water-soaked lesions progressing to necrotic patches on leaves, along with systemic colonization of crown tissues showing water-soaked, reddish-brown lesions without cavity formation. Additionally, resistance evaluation across six strawberry cultivars revealed that 'Yue Xiu' was the most susceptible, followed closely by 'Jiande Hong', 'Hong Yu', 'Li Fen', and 'Hong Yan', while 'Fen Yu' exhibited the highest resistance. Biological characterization showed that strain JD1 grows optimally at 25°C and pH 7.0, with significant inhibition observed at 35°C and under acidic (pH 4) or alkaline (pH 9) conditions. In bactericide screening, tetramycin and benziothiazolinone were identified as highly effective against JD, followed by sintracin acetate aqueous with minor efficacy, whereas kasugamycin and quinoline copper showed limited or no efficacy. Collectively, these findings not only emphasize the threat posed by <i>X. fragariae</i> strain JD1 to strawberry production but also provide critical insights that inform integrated management strategies, including the use of resistant cultivars, environmental controls, and targeted bactericides, for controlling ALS.