Dissecting Parameters Associated with Sheath Rot ( Sarocladium oryzae [(Sawada) W. Gams & D. Hawksw]) Disease in Rice ( Oryza sativa L.

Accurate measurement of parameters contributing to diseases and their symptoms is important for identification of resistant genotypes. Present sheath rot scoring system such as disease incidence scoring system accounts for only percentage of disease incidence and not the disease severity. Disease severity scoring system is based on combined features of panicle exertion and lesion size, very laborious and less accurate in field condition. Existing disease index requires assigning of incidence-severity scores for each and every tillers in a plant and has greater difficulties in evaluation of large number of plants or breeding pools. Hence, we propose phenotypic parameters such as proportion of panicle exertion, proportion of diseased and healthy sheath and modified disease severity scoring system for accurate measurement of disease. A high-throughput and simple disease indices (severity index, lesion index, detached lesion index and panicle discolouration index) are proposed for accurate identification of resistant-susceptible genotypes.