IDENTIFICATION OF A UNINUCLEATE RHIZOCTONIA SP BY PATHOGENICITY, HYPHAL ANASTOMOSIS AND RAPD ANALYSIS

Finnish and Norwegian uninucleate Rhizoctonia sp. isolates, originatin g from roots of nursery grown conifer seedlings suffering from root di eback, and having Ceratobnsiditli71 perfect stale, were tested for pat hogenicity and genetic relatedness. All tested isolates of this pathog en considerably reduced the root system development of Scots pine and Norway spruce seedlings resulting in death or stunted growth. The unin ucleate isolates anastomosed readily with each other producing a killi ng reaction. In a RAPD-PCR analysis, the uninucleate isolates had diff erent banding patterns from our reference isolates, two Finnish binucl eate isolates (AG-I and R. sp.) and standard tester isolates of genus Ceratobasidium representing anastomosis groups AG-A, AG-C, AG-E, AG-G and AG-I. UPGMA analysis clustered the uninucleate isolates together a t a greater similarity than 75% while the binucleate isolates formed d istinct clusters and were 10-25% similar to the uninucleate Rhizoctoni a sp. Hyphal anastomosis and DNA data suggest that the uninucleate Rhi zoctonia sp. is an homogeneous group and distinct from the tested binu cleate Rhizoctonia isolates.