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Identification, Isolation Frequency, and Pathogenicity of Anastomosis Groups of Binucleate Rhizoctonia) spp. from Strawberry Roots. S. B. Martin, Department of Plant Pathology and Ecology, The Connecticut Agricultural Experiment Station, 123 Huntington Street, P.O. Box 1106, New Haven 06504; Phytopathology 78:379-384. Accepted for publication 17 June 1987. Copyright 1988 The American Phytopathological Society. DOI: 10.1094/Phyto-78-379.

Rhizoctonia spp. were isolated from roots of strawberries (Fragaria ananassa) in Connecticut during the spring of 1985 and 1986 and the fall of 1986. R. solani (AG-5) was isolated infrequently (2.7% in 1985; 3.1% in 1986) in comparison with binucleate Rhizoctonia spp. Three anastomosis groups (AG) were identified among the binucleate Rhizoctonia spp.: AG A, AG G, and AG I. Isolates grouped in AG G were obtained more frequently than those in AG A or AG I in spring samples (42.9 vs. 26.1 and 15.4% in 1985, and 56.1 vs. 14.0 and 26.8% in 1986). There was a higher percentage of recovery of AG I compared with AG G or AG A in samples collected in fall 1986 (72.7 vs. 14.7 and 7.9%, respectively). Frequencies of isolation of isolates in particular anastomosis groups differed among farms and among fields within farms. Isolates obtained from different roots of the same plant usually belonged to the same anastomosis group. Isolates obtained from each anastomosis group were pathogenic, but at 15 C, those belonging to AG I induced significantly greater disease severity on strawberry than AG A or AG G isolates.

Additional keywords: black root rot, Ceratobasidium sp., soilborne pathogens.