Molecular characterization and pathogenicity of binucleate Rhizoctonia AG-F associated to the watermelon vine decline in Italy

In recent years, watermelon (Citrullus lanatus) has been subjected to significant losses due to vine decline in Sicily (southern Italy). During a survey conducted in 2009, the predominant fungal species associated with root rot and vine decline were Rhizoctonia spp. The most isolates were characterized as binucleate Rhizoctonia AG-F through morphological observation, nuclear condition, anastomosis tests and sequence homology of rDNA-ITS. Occasionally, R. solani was found. The pathogenicity of binucleate Rhizoctonia and virulences of different isolates were tested in growth chamber on watermelon seedlings. All isolates were pathogenic on watermelon seedlings and showed statistically significant differences on the disease incidence and severity among them. To our knowledge, this is the first report worldwide of the occurrence of pathogenic binucleate Rhizoctonia responsible for root rot and associated with watermelon vine decline.