First report of melon decline caused by Plectosphaerella cucumerina in Iran

In spring 2019, melon plants (cucumis melo cv. janna) with collapse and decline symptoms were collected from fields in dashti county, bushehr province in southern iran. twelve morphologically similar isolates from infected root and crown tissues were recovered. fungal isolates were identified based on morphological characteristics and molecular data of the internal transcribed spacer (its-rdna) region. according to the morphological and phylogenetic analysis, the isolates were identified as plectosphaerella cucumerina. the pathogenicity test was performed on healthy seedlings of melon plants (cvs. kharboze-mashhadi and shahde-shiraz). three weeks after inoculation, the melon seedlings showed root rot, necrosis and wilting symptoms then eventually death. to complete the koch's postulate, p. cucumerina was re-isolated from inoculated plants. this is the first report of p. cucumerina causing decline on melon in iran.