CHARACTRIZATION OF ANASTOMOSIS GROUPS AND EVALUATION OF PATHOGENICTY OF Rhizoctonia solani ISOLATES INVOLVED IN FLAX SEEDLING BLIGHT.

Abstract

Forty 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.