Studies on Variability of Pyricularia oryzae and Management of Rice Blast Disease

Abstract

newline Investigations on rice blast disease were undertaken to study the status of rice blast in Jammu division, effect of weather parameters on the disease development, variability of the pathogen and management of disease through germplasm evaluation, biological, and chemical means. During the survey of various districts of Jammu division, the overall range of the disease severity in Jammu division ranged between 7.23-35.56 per cent and 9.12-37.22 per cent during cropping seasons 2018 and 2019, respectively. The disease progress exhibited sigmoidal pattern of the curve during both the years. The maximum infection rate (r) was observed during 41th Standard Meteorological Week. Temperature (max. and min.), relative humidity (evening), rainfall and bright sunshine hours showed negative correlation with disease severity during both the years. newlineThe colony colour of thirty isolates collected during the survey were off white to greyish black, with circular or irregular margins and flattened to raised growth pattern. Mycelial diameter varied from 8.1 to 90 mm in five different culture media. Significantly higher mycelial diameter was recorded in oat meal agar medium while it was the least in Czapek s dox medium. The conidial length ranged between 8.67 to 15.51 and#956;m and conidial breadth ranged between 3.22 to 7.73 and#956;m in all the isolates. The maximum spore size was recorded in isolate Po25 (13.80-15.51 × 6.20-7.73and#956;m) and it was the minimum in isolate Po5 (8.67-10.30 × 3.22-5.46 and#956;m). The incubation period of all the P. oryzae isolates ranged from 5.9 to 8.6 days in different rice varieties. The molecular analysis using 25 SSR primer pairs revealed a remarkably higher level of genetic polymorphism in the twenty three isolates of P. oryzae. None of the genotypes was found highly resistant to rice blast while nine germplasm viz; JKRH-2609, IRH-117, IRH-118, HRI-198, NS-6688, NPH-X2, US-321, CRH-006 and Indam-200-048 were resistant. Under in vitro studies maximum growth inhibition (43.99%) was recorded by biocontrol age