Abstract

Maurice S. Mikhail1, Kamel K. Sabet1, Moawad R. Omar2, Amal A. Asran3andKhaled K. Kasem1,4*

Twenty eight isolates of Rhizoctonia solani were obtained from cotton seedlings and twenty three isolates from other hosts; eight from peanut, five from chickpea, two from each of flax, tomato and watermelon and one from each of potato, cantaloupe, pepper and lupine. Microscopic examination revealed that 17 isolates (33.33%) each belonged to AG-2- 2, 17 and AG-4 HG-I, while 7 isolates (13.73%) belonged to AG -4 HG-II and 10 isolates (19.61%) belonged to AG-5. Pathogenicity test on cotton cultivar Giza 86, under greenhouse conditions, showed that 19 isolates significantly induced pre- and post-emergence damping-off, while they significantly decreased survival, plant height and dry weight. However, the pathogenic isolates of AG-2-2 represented 19.61% of the total isolates as well as the highest percentage of the pathogenic isolates (52.63%). There were no significant differences between effects of different AGs on the cotton seedling variables. Cluster analysis suggested that grouping the isolates based on their virulence patterns was not related to their geographic origins, AG or host.