orty eight isolates of Rhizoctonia solani were obtained from flax seedlings showed seedling blight. Anastmosis tests revealed that 12 isolates (25%) belonged to AG-2, while 36 isolates (75%) belonged to AG-4. Pathogenicity test on flax cultivar Shkha 1, under greenhouse conditions, showed that the pathogenic isolates in the pre-emergence stage represented 91.67 and 77.72% within AG-2 and AG-4, respectively. However, the pathogenic isolates of AG-4 representing 58.23% of the total isolates as well as the highest percentage of the pathogenic isolates (71.79%). This observations held true in the case of plant height and dry weight. These results indicate that both AGs 2 and 4 are important in the etiology of flax seedling blight. The importance of AG-2 is due to its high virulence, while the importance of AG-4 is due to its high prevalence .Cluster analysis suggested that, within each AG, isolates could be separated into subgroups with specific virulence patterns.