MORPHOLOGICAL AND MOLECULAR CHARACTERIZATION OF Rhizoctonia solani CAUSING SHEATH BLIGHT AND ITS REACTION PATTERN TO RICE GERMPLASM

Abstract

The experiment was conducted for morphological characterization, molecular identification and to study pathogenic variation among Rhizoctonia solani isolates collected from different areas of Bangladesh. The experiment was performed in the laboratory of Plant Pathology Division, Bangladesh Rice Research Institute (BRRI), Gazipur during the period of June 2019 to February 2020. Eight isolates were isolated from seven different areas in Bangladesh and all isolates showed wide morphological variation in terms of size of sclerotia (1.62 mm to 4.38 mm), colony colour and texture of sclerotia ranging from dark brown to light brown with rough to smooth in texture. Initiation of sclerotia formation time was varied from 4 to 6 days. Based on the colony pigmentation, all the isolates were assigned into 4 groups: dark brown, dirty white, milky white and yellowish brown. All the isolates had growth rates between 5.00-5.87cm² per day with an average of 5.33cm²/day. All the isolates except RS-2 and RS-7 were confirmed as Rhizoctonia solani with the molecular identification using the primer pair ITS1/ITS4 and showed band around 700bp. No genetic variation was found among the isolates. A field trial with 35 rice germplasm was conducted during the Transplanted Aman season to screen the Rhizoctonia solani resistant germplasm in BRRI research field. BR11 was used as susceptible variety. Highest relative lesion height (97%) was recorded in susceptible check BR11. The lowest relative lesion height (15%) was recorded in genotype Var24. It was revealed that three genotypes (Var23, Var24 and Var29) were found resistant out of 35 genotypes tested. These germplasm could be used in future rice breeding programmes aimed at improving resistance to sheath blight.