Assessment of Losses and Identification of Slow Blighting Genotypes against Sheath Blight of Rice

摘要

Rice (Oryza sativa L) is an important cereal crop which is grown over a large area especially in Asian countries. Amongst the various diseases occurring on rice, sheath blight caused by Rhizoctonia solani Kuhn is one of the major fungal diseases in India. The present investigations have revealed that the losses in grain yield at more or less same disease severity differed with cultivars. There was no significant reduction in grain yield of plots inoculated at 60 (stem elongation) and 75 days after transplanting (booting) when vertical disease spread ranged between 38.43 to 49.78 per cent in Basmati CSR 30, while there was 11.1 land 4.04 per cent reduction in grain yield with a vertical disease spread of 51.54 and 37.05 per cent in non-scented variety HKR 127. Out of fifty scented and non-scented rice genotypes evaluated, five genotypes viz. N-22 (Acc. 6264), N-22 (Acc. 4819), HKR 05-476, Tetep and N-22 (Acc. 19379) exhibited slow blighting against sheath blight as the disease progress was significantly reduced. The apparent infection rate and area under disease progress curve was considerably lower in these genotypes. Moreover, in most of these genotypes, the incubation period was delayed and there was no sclerotia formation till maturity of the plants. Comparison of scented and non-scented rice genotypes with respect to sheath blight development showed that the vertical disease spread was more in non-scented high yielding rice genotypes/cultivars with high tillering ability than the tall scented cultivars with fewer tillers. It might be attributed to production of closed canopy and a favourable microclimate for disease development much earlier in short statured cultivars than the tall ones. The apparent infection rate (r) and AUDPC were also foundto be considerably higher in non-scented genotypes vis-a-vis scented genotypes. Based on these observations, it could be inferred that slow blighting trait against sheath blight is more common among scented rice genotypes then non-scented ones.