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Rhizoctonia disease, caused by Rhizoctonia so/ani is one of the most important fungal diseases of potato in Khorasan. From t05 isolates of
Rhizoctonia collected from different potato fields, 75 isolates belonged to AG3. 11 to AG4. 5 to AG2-1 of R. solani and 13 to binucleate groups. One
isolate did not anastomos with any of the tester cultures including (AG!
(IA-IB-IC)- AG2(1-2)- AG_- AG4- AGS- AG6- AG7- AG9- AGtl- AG- BI).
In vitro the growth rate of AG4 isolate was significantly faster than AG3 and AG2-1 above IS' C while the growth rate of AG_ was faster than AG4 and AG2-1 below IS' C. Members of AG_, AG4 and AG2-1 were not restricted to
any particular geographical region of the province. AG_ isolates were more virulent than AG4 and AG2-1 isolates. All isolates [rom tuberborn sclerotia
were belonged to AG_. The high incidence and virulence of AG3 isolates indicate that AG_ is the major cause of rhizoclonia disease in Khorasan
province. where as. AG4 and AG2-1 arc of minore importance. The protein profiles for the three AGs were distinctive and could be distinguished from
one another. The protein patterns from isolates belonging to AG_ and AG2-1 were uniformly distinct. Protein patterns of isolates beloging to AG4 varied in
bands.