Characterization of Rhizoctonia species involved in tree seedling damping-off in French forest nurseries

A total of 166 Rhizoctonia isolates were obtained from damped-off pine seedlings grown on soils originating from two bareroot forest nurseries in France. A majority of these isolates, 70%, had multinucleate cells and were identified as Rhizoctonia solani. R. solani isolates could be assigned to three anastomosis groups: AG 2-1, AG 4 the most prevalent one and AG 5. They were all pathogenic to pine seedlings. Isolates belonging to AG 5 were most aggressive, resulting in postemergence damping-off in 99% of the test seedlings, Pinus nigra subsp. Laricio. The damping-off severity for AG 4 and AG 2-1 were 68 and 25% respectively. Possible thermic affinities of AG 2-1 and AG 4 isolates were discussed. (C) 1998 Elsevier Science B.V.