Identification and validation of sheath blight resistance in rice (Oryza sativa L.) cultivars against Rhizoctonia solani

Rice sheath blight, caused by Rhizoctonia solani, is a devastating disease of rice which causes major yield loss in most rice growing regions of the world. Hence, identification and subsequent development of disease resistance in rice cultivars is crucial. Six moderately resistant cultivars, namely 'Teqing', 'Jasmine85', 'Tetep', 'Pecos', 'Azucena' and 'Taducan', one susceptible local cultivar, 'MR 219', and two new advanced breeding lines, 'UKMRC 2' and 'UKMRC 9', were screened using micro-chamber and mist-chamber methods. The fungal isolate was confirmed as R. solani using ITS-rDNA sequencing. Severe sheath blight was recorded following inoculation with R. solani under micro-chamber conditions. The most resistant cultivar was 'Tetep', followed by 'Teqing'. In mist-chamber screening, 'UKMRC 2' showed the highest level of susceptibility with a disease severity index (DSI) of 6.67, while 'MR 219' produced the highest DSI of 7.22 in the micro-chamber. Significant correlation of plant height and disease was obtained with relative lesion height (RLH) indices. Significant correlations were also observed among diseased plant affected area (DPAA), VRT (visual rating) and RLH, with VRT being the most accurate. On the basis of the disease reactions, 'Tetep' and 'Teqing' were identified as suitable donors to improve resistance in 'UKMRC 2' and 'MR 219'. Mist-chamber screening method was more reliable to evaluate sheath blight under greenhouse conditions than the micro-chamber method.