Morphological characterization and screening for sheath blight resistance using Indian isolates of Rhizoctonia solani AG1IA

Sheath blight of rice caused by Rhizoctonia solani AG1IA is one of the devastating fungal diseases. One hundred and twelve R. solani AG1IA isolates collected from Uttar Pradesh, Uttarakhand and Haryana states of India were studied for their morphological characterization. All the isolates of R. solani AG1IA were classified into five groups on the basis of sclerotial arrangements i.e. Group-1, Group-2, Group-3, Group-4 and Group-5 which contains 28, 35, 44, 3 and 2 isolates, respectively. Majority of the isolates were spatial in growth pattern (38.3%), fast growing (40.1%), light brown colony colour (72.3%), scattered sclerotia (39.2%), deep dark brown sclerotia (91.0%), sclerotial clump formation (32.1%) and micro sized sclerotia (56.2%). The number of sclerotia produced was in the range of 3.7–10.7/5 mm mycelium disc. Two isolates RSV10 and RSJ79 did not produce any sclerotia. Time of initiation of sclerotia formation was varied between 4 and 6 days. Sixty-five isolates showed sclerotia formation on under surface of lid. Principal component analysis (PCA) of growth rate and number of sclerotia of R. solani AG1IA showed 100.00 and 86.84% variation, respectively. A field trial with 261 rice germplasm was conducted during the 2013–2014 and 2014–2015 Kharif seasons to screen the R. solani AG1IA resistant germplasm. Mean percent disease index (PDI) varied between 22.95 and 27.40%. On the basis of AUDPC (area under disease progress curve) values, rice germplasm lines belonged to 5 groups i.e. resistant, 57 (262.93–957.92), moderately resistant, 169 (957.93–1220.87), moderately susceptible, 14 (1220.88–1490.81), susceptible, 18 (1490.82–1753.75) and highly susceptible, 3 (1753.76–2016.69).