Morphological and Molecular Characterization of Species Causing Leaf Blight on Watermelon in China.

Watermelon is an economically important crop in China and is commonly affected by -like leaf blight that can result in significant economic losses. In this study, 830 isolates, recovered from symptomatic watermelon leaves, were identified based on morphological traits, pathogenicity, and multilocus sequence analyses of glyceraldehyde-3-phosphate dehydrogenase (), histone 3 (), the internal transcribed spacer of ribosomal DNA (rDNA ITS), and the RNA polymerase II second largest subunit (). Watermelon isolates grouped to five species and one unclassified species. They were , , , , , and sp. Notably, was the most prevalent (73.5%) of the six isolated species, followed by (25.0%), (1.1%), sp. (0.2%), (0.1%), and (0.1%). Pathogenicity tests demonstrated that all six species could produce brown necrotic lesions on detached leaves of watermelon. The average disease incidence (75.1%) and average disease index (60.8) of watermelon resulting from inoculation of leaves with were significantly higher than levels resulting from (52.9% and 37.2) and (47.5% and 30.8). Inoculation with sp. resulted in a disease incidence (70.0%) and disease index (51.5), which were lower than those of . The disease incidence and disease index in watermelon leaves inoculated with the one isolate of and the one isolate of present in the inoculated leaves were 28.9% and 16.4, and 48.9% and 31.4, respectively. Results of the study indicate that species associated with watermelon leaf blight in China are more diverse than that has been previously reported. This is the first report globally of , , and an unclassified species as causal agents of leaf blight on watermelon.