First report of Rhizoctonia solani and binucleate Rhizoctonia from Johnsongrass in Turkey

Johnsongrass (Sorghum halepense) is a weed in agricultural fields in Turkey. In 1998 and 1999, during a study to determine fungal species associated with Johnsongrass, plant samples were collected in the Yusufeli and Olur district of Artvin and Erzurum provinces, respectively. Necrotic bases of stem tissues were surface-treated in 0.5 % sodium hypochlorite for 1 min, placed on 1.5 % water agar containing 50 mg/l streptomycin sulfate, and incubated at 20-25° C for 48-72 h. Hyphae from the margin of each developing colony were transferred to water agar or potato dextrose agar (PDA). Thirty cultures of Rhizoctonia were isolated and identified based on vegetative hyphae, nuclear condition, and hyphal anastomosis with known tester isolates of Rhizoctonia solani and binucleate Rhizoctonia (Sneh et al., 1991). Of these isolates, two were identified as R. solani (one AG-4 and one AG-5) and 28 as binucleate Rhizoctonia. The binucleate Rhizoctonia isolates were identified as AG-A, AG-G, and AG-K (6, 16, and 6 isolates, respectively). Rhizoctonia solani AG-4 and AG-5, binucleate Rhizoctonia AG-G (13 isolates) and AG-K isolates were obtained from Yusufeli; binucleate Rhizoctonia AG-A and AG-G (3 isolates) isolates were obtained from Olur. Pathogenicity of all isolates was determined on four-week-old Johnsongrass seedlings at 25°C. Seedlings were inoculated by gently removing the soil mixture from one side of the stem, placing a colonised PDA plug (4 mm diameter) in direct contact with the base of the stem and covering the inoculum with the soil mixture. Control seedlings were inoculated in a similar manner by placing a sterile PDA plug on the base of the stem. Six weeks after inoculation brownish, sunken lesions were observed on the base of stems of seedlings inoculated with all anastomosis groups. Stems of noninoculated seedlings were free of lesions. Cultures of each Rhizoctonia group were reisolated from plants of their respective treatments. This is the first reported observation of R. solani and binucleate Rhizoctonia isolates on Johnsongrass from Turkey.