Characterization, Virulence, and Genetic Variation ofRhizoctonia solaniAG-9in Alberta

Abstract

A total of 130 Rhizoctonia solani AG-9 isolates were isolated from agricultural soils collected in 1992 and 1993 in central and northeastern Alberta. On potato dextrose agar, cultures developed a brown to tan mycelium and irregularly shaped, brown to dark brown sclerotia (0.5 to 2.0 mm), singly or in clumps. Number of nuclei per vegetative hyphal cell ranged from 3 to 17. Less than 20% of the isolates were thiamine auxotrophic. In a petri plate test, all isolates were virulent to canola, causing seed rot and seedling infection. In a greenhouse test, AG-9 isolates were mildly virulent to canola. Two isolates were further tested for virulence to 10 different crops. These isolates were highly virulent to cauliflower and moderately virulent to flax, causing significant pre-emergence damping-off. Isolates of AG-9 also were mildly virulent to canola in which emergence was reduced and root discoloration was observed. Isolates were avirulent to alfalfa, pea, tomato, wheat, barley, oat, and bromegrass, though slight root discoloration on seedlings of alfalfa, wheat, oat, and bromegrass was observed. Genetic variation of 12 isolates from Alberta and 3 from Alaska was analyzed by random amplified polymorphic DNA (RAPD) assay using different oligonucleotide primers. There was considerable variation within the R. solani AG-9 group; this suggests that AG-9, considered indigenous to Alaska, is present in a variety of environments and different geographic areas. It is a heterogeneous group and the genetic variation within the AG-9 group can be identified by the RAPD-polymerase chain reaction technique.