Variability in isolates of Rhizocfonia solani Kuhn, the sheath blight fungus of rice

One hundred and seventy eight isolates of Rhizoctonia solani Kuhn collected on different rice varieties from eighteen districts belonging to five agro-climatic zones of Odisha were studied for their variability. Based on the mycelia and sclerotial characters, the isolates were grouped into eighteen cultural types. Three types of mycelia viz. white, brown and deep brown were observed. The white mycelia of the isolates were thin (6.5–9.5μ) and all the brown and deep brown mycelia were thick (10.5–15.2μ). There was rapid and heavy mycelial growth (81-95mm) with scloretial production (70–88) in respect of the isolates from Cuttack, Kendrapara, Jagatsinghpur, Balasore, Bhadrak, Jajpur, Dhenkanal, Jharsuguda and Gajapati districts. The mycelial growth was very poor (33-52mm) along with scloretial production (23–39) in afew isolates from Cuttack, Kendrapara, Jagatsinghpur, Bhadrak, and Jajpur and in all the isolates from Angul, Sambalpur and Ganjam. Ten highly virulent, six moderately virulent and two avirulent isolates were identified in the population structure of the isolates studied.