Phenotypic and molecular characterization of Xanthomonas citri pv. malvacearum isolates obtained from bacterial blight diseased cotton plants in Greece

Bacterial blight of cotton (Gossypium hirsutum L.), caused by Xanthomonas citri pv. malvacearum, induces serious economic damage throughout all major cotton producing areas in the world. In 2020, the disease was confirmed in five commercial fields in the Regional Unit of Drama in Greece with yield losses reaching 30%. The symptoms on leaves included angular necrotic spots, narrow necrotic stripe along the veins of the leaf and dark lesions on petioles. On bolls circular water-soaked spots, brown necrotic spots and large irregular necrotic areas developed, eventually resulting in boll rot. Xanthomonas citri pv. malvacearum was isolated and subsequently identified morphologically, biochemically and molecularly, based on PCR with the specific primers MSCT1-P2F/ MSCT1-P2R and partial 16S rRNA gene sequencing. The pathogenicity of the isolates was confirmed using artificial inoculations on cotton seedlings with subsequent re-isolation and re-identification. This is the first time that the causal agent of bacterial blight of cotton, Xanthomonas citri pv. malvacearum, although earlier observed and isolated, is fully identified by biochemical, molecular and pathogenicity tests in Greece.