IN-VITRO ANALYSIS OF HOST-PLANT SPECIFICITY IN RHIZOCTONIA-SOLANI

Rhizoctonia solani is a plant pathogenic fungus with a wide host range . Host plant specificity within R. solani was analysed on seedlings gr own aseptically on agar, which allowed continuous observation of both the fungus and the whole plant without disturbing the interaction. Sym ptom development on cauliflower, Arabidopsis, eggplant, tomato and pot ato by 32 R. solani isolates, belonging to six different anastomosis g roups (AGs), was studied. Host plant specificity of isolates, as analy sed by similarity clustering, was similar to AG-related host plant spe cificity as observed in the field, with AG3 isolates (except two aviru lent strains) separating from the other isolates. Two R. solani isolat es with a reciprocal pathogenicity on cauliflower and tomato were sele cted for further studies. These showed that in the pathogenic combinat ion, R. solani isolates grew over the plant, adhered and formed infect ion structures, while in the nonpathogenic combination isolates grew o ver the plant, but neither adhesion nor the formation of infection str uctures occurred. From these data, it was concluded that host plant sp ecificity is mediated in the early steps of the infection process.