Rhizoctonia solani Kühn, teleomorph Thanatephorus cucumeris (Frank) Donk is one of the important sugar beet soil borne pathogen and can damage any part or all of a plant. Isolates divided into types or groups (AGs) based on the anastomosis behaviour of individual isolates. Crown and root rot is primarily caused by AG2-2, while damping-off in seedling and foliar blight signs are generally attributed to AG4. the various AG types represent genetic deversity within the species. Three R. solani isolates collected from different localities at West-Nubaria region, showing characteristic sugar beet crown and root rot symptoms, were chosen and compared to the well- characterized R. solani (tweleve isolates) obtained from different hosts.
All fifteen R. solani tested isolates observed show different levels of pathogenicity by inducing chlorosis, wilting, crown rot, root rot and damping-off on inoculated sugar beet. Data based on the morphological characteristices of the pathogen, pathogenicity tests, hyphal compatibility reaction and sequencing analysis of the ITS region (internal transcribed spacer) of ribosomal DNA of the tested isolates in order to detect their relatedness. Sequence analysis showed that these isolates were varied genetically, where data could be genotype them into two main clusters including AG2-2 and AG4 groups. Additionally, phylogenetic tree recorded the relationship between ITS sequence of rDNA for those tested isolates.