Characterization of mycorrhizal isolates of Rhizoctonia solani from an orchid, including AG-12, a new anastomosis group

• Published in: Phytopathology 1999-10, Vol.89 (10), p.942-946
• Main Authors: Carling, D.E, Pope, E.J, Brainard, K.A, Carter, D.A
• Format: Article
• Language: English
• Subjects: anastomosis groups; Biological and medical sciences; Brassica oleracea var. botrytis; color; compatibility; cultured cells; Fundamental and applied biological sciences. Psychology; Fungal plant pathogens; genetic variation; Hordeum vulgare; Lactuca sativa; mycorrhizae; pathogenicity; Phytopathology. Animal pests. Plant and forest protection; plant litter; Pterostylis; Raphanus sativus; seedlings; Solanum tuberosum; Thanatephorus cucumeris; Variation, races, biotypes, parasitic specialization, genetics
• ISSN: 0031-949X; 1943-7684
• DOI: 10.1094/PHYTO.1999.89.10.942

Isolates of Rhizoctonia solani collected from mycorrhizal orchid (Pterostylis acuminata) plants and adjacent leaf litter were characterized. Of 23 selected isolates, 20 were members of a new anastomosis group AG-12) and the rest were members of AG-6. There were no bridging anastomosis reactions observed between AG-12 and other AGs of R. solani. Among the 20 isolates of AG-12 evaluated, 18 vegetatively compatible populations were detected, indicating diversity within the AG. Mature cultures were dark brown, as were mature sclerotia. Some cultures produced alternating dark- and light-colored concentric rings, with sclerotia forming in the darker rings. Most cultures were appressed to the agar surface. In tests run to characterize pathogenic potential, selected mycorrhizal isolates of AG-12 and AG-6 did little damage to potato and barley seedlings, moderate damage to head lettuce seedlings, and more extensive damage to seedlings of cauliflower and radish. Isolates of AG-12 have not been observed to fruit in nature, and all attempts to induce formation of the teleomorph (Thanatephorus cucumeris) in the laboratory by selected isolates of AG-12 failed.