GENETIC DIVERSITY AMONG ISOLATES OF RHIZOCTONIA-SOLANI AND SOURCES OFRESISTANCE IN VICIA-FABA

The virulence of nine isolates of Rhizoctonia solani (AG-2T2, AG-4, an d AG-5) from Vicia faba on 20 V. faba genotypes of diverse origin was investigated under controlled greenhouse conditions. Infested PDA disc s were used as inoculum. A wide range of virulence was displayed among the R. solani isolates on the different faba bean genotypes. Isolates RS-5(AG-5) and RS-6 (AG-4) were the least virulent on most faba bean genotypes. Isolates RS-2 (AG-4), RS-12 (AG-4), RS-13 (AG-2T2), RS-20 ( AG-2T2), RS-58(AG-4), and RS-59 (AG-2T2) were moderately virulent on 3 -10 genotypes. Isolate RS-1 (AG-4) was highly virulent on all genotype s. A large number of faba bean accessions and cultivars were evaluated under field conditions for their reaction to R. solani isolates RS-12 and RS-58 (AG-4). A 1:1 mixture of proso millet seed infested with ea ch of the two isolates was used as inoculum at the time of seeding. Mo re than 60% of the plants were resistant to seed rot in 25 accessions, to seedling blight in 171 accessions, and to both diseases in 5 acces sions. The percentages of plants resistant to seedling blight declined after each of three cycles of selection, selfing, and testing to isol ate RS-58 under controlled conditions.