Isolation and Characterization ofRhizoctonia solaniand BinucleateR. solani-like Fungi from Aerial Stems and Subterranean Organs of Potato Plants

Abstract

Lesion, hymenial, and sclerotial isolates of Rhizoctonia solani were collected from potato plants growing at various locations in Alaska [USA]. Most lesion and hymenial isolates were members of anastomosis group 3 (AG-3). Isolates assigned to AG-2-1 were obtained from lesions and hymenia collected at two locations and from sclerotia collected at a third. Lesion development was usually extensive on AG-3-infected plants but minor or undetectable on plants associated with other isolates. Three lesion and three hymenial isolates were identified as binucleate R. solani-like fungi. Eight multinucleate isolates failed to anastomose with R. solani tester isolates representing AG-1, AG-2-1, AG-2-2, AG-3, AG-4, AG-5, AG-6, AG-7, AG-8, or AG-BI, but they did anastomose with one another, constituting an anastomosis group not yet identified. In 57 cases, both hymenial and lesion isolations were made from the same plant. On 51 of these plants, the anastomosis group of lesion nd hymenial isolates matched, whereas on six plants, lesion and hymenial isolates did not match. Anastomosis of matched pairs of AG-3 isolates generally resulted in perfect fusion without cell death, indicating pairs were members of the same clone. Anastomosis of matched pairs of AG-2-1 isolates generally resulted in perfect fusion with cell death, indicating dissimilarity of clones. AG-3 isolates from lesions, hymenia, and sclerotia were moderately to highly virulent on potato sprouts, but AG-2-1, undesignated multinucleate, and binucleate R. solani-like isolates were mildly virulent or avirulent. Comparative pathogenicity of isolates on germinating cauliflower seeds also was determined.