First report of bacterial leaf spot on watermelon caused by Pseudomonas syringae pv. syringae in Georgia.
In May 2015, leaves of watermelon (Citrullus lanatus) cv. Melody were observed with circular to irregularly shaped spots, each with a tan centre and dark margin in a field in Cook Co., Georgia, USA. The field exhibited 20 to 25% disease incidence with no symptoms on fruits. Symptomatic leaves with leaf spot were collected, and bacterial isolations were made on King's medium B agar. Based on morphological, biochemical, physiological, molecular (amplifying and sequencing the 16S rRNA gene) and pathogenicity tests, the causal agent was identified as P. syringae pv. syringae [P. syringae]. This is thought to be the first report of P. syringae pv. syringae in watermelon in Georgia. Being a known seedborne bacterium of watermelon, it is possible that the pathogen might have been introduced through contaminated seeds.