CHARACTERIZATION AND PATHOGENICITY OF ANASTOMOSIS GROUPS OF RHIZOCTONIA SOLANI ISOLATED FROM SUGARBEET IN EGYPT

Abstract

Fourty-three isolates of Rhizoctonia were collected from sugar-beet seedlings and older plants from different fields in Egypt during 1992-1993. Of the isolates collected, only one was binucleate and the remaining 42 isolates were multinucleate with characteristics typical of R.solani. R.solani isolates belonged to three anastomosis groups : AG-2-2 (28.6%), AG-4 (64.3%) and AG-5 (7.1%). All isolates from rotted roots were AG-2-2, while 81.8% of AG-4 isolates from seedlings. Pathogenicity tests on sugarbeet seedlings in the greenhouse showed that isolates of AG- 4 were most pathogenic in causing seedling damping-off compared with AG-2-2 and AG-5, while AG-2-2 isolates were more virulent in caus­ing root-rot to older sugar beet plants. The binucleate isolate of Rhizoctonia was nonpathogenic and increased growth of sugarbeet seedlings. The binucleate isolate significantly reduced damping-off caused by R.sol