Identification and characterization of collapse on tomato and cucumber caused by Plectosphaerella cucumerina in Iran

In summer 2015, cucumber and tomato plants with collaps and decline symptoms were collected from fields in Bajgah and Kaftarak regions in Fars province and transported to the laboratory. After isolation of the causal agent, single spore colonies were derived prior to morphological identification. Colonies on PDA plates were buff or salmon pink; the mycelium was slimy with sparse or absent aerial hyphae. Conidiophores were solitary, unbranched or rarely irregularly branched and the conidiogenous cells could be described as phialidic, hyaline and smooth. Occasionally the conidiogenous cells showed one septa near the base. Conidia were aggregated in slimy heads, hyaline, ellipsoidal, tapering gradually to rounded apex and base, septate or aseptate. These characteristics are typical of Plectosphaerella cucumerina (Lindf.) W. Gams. (anamorph: Plectsporium tabacinum). The internal transcribed spacer (ITS) region of the isolates was amplified using primers ITS1 and ITS4 and sequenced. Blast analysis of the sequences showed identity of the isolates to P. cucumerina. Based on sequence analysis of ITS region, the fungal isolates showed nucleotide variation. Bajgah and Kaftarak isolates were identified as two molecular subgroups. Pathogenicity tests were also conducted on tomato, cucumber, pepper, watermelon and melon plants. 3-4 weeks after inoculation, 70% inoculated plants showed symptoms including wilting, root and collar rot, dwarfing of stem and root and death of seedling. This is the first report of P. cucumerina causing tomato and cucumber collapse in Iran with characterization of the fungus based on morphological, pathogenicity and molecular data.