The evaluation of the reaction of some cultivar of bean into five pathogenic isolates of Rhizoctonia solani in Green house

Common bean (phaseolus vulgaris) has the most under-cultivation areas among cereals in the world and is very important because it contains 22% protein in food diet. Rhizoctonia root rot and crown rot of bean caused by Rhizoctonia solani is one of the most important disease of this crop in Iran. In this study, during 2005-2006, plant and soil samples were gathered from the main under-cultivation areas in Tehran province and totally, 81 isolates of the fungus were isolated, purified and maintained.The morphological characteristics of the isolated including the color of colony, aerial mycelia, sclerotia (regarding form and size), the width of hyphae and the numbers of nuclei per cells were surveyed. 16 improved cultivars of navy bean, kidney bean, French bean, green bean and black –eye bean were used to identify resistant ones. The mentioned cultivars were tested for resistance to the 5 highest pathogenic isolates Rs7, Rs18. Rs21, Rs62 and Rs74 in greenhouse using complete randomized blocks design with 4 replication (15 seeds / pot). Results showed that not only none of the cultivars were completely resistant, but also all of them were susceptible and semi-susceptible and just two cultivars Goli and Sayad kidney bean with the average disease severity 2.58 and 2.9 (using the scale 1-5) were semi-resistant to the disease.