Screening of Rice Genotypes against Brown Spot Disease at Rampur, Chitwan, Nepal

Brown spot of rice caused by Bipolaris oryzae (Breda de. Haan) Shoemaker is one of the major constraints of rice production in all rice growing regions of Nepal. To identify and select the sources of brown spot resistance in rice genotypes, a field experiment was conducted under the natural epiphytotic condition at National Maize Research Center, Rampur, Chitwan in 2022. A total of 10 genotypes, including susceptible check (Sabha Mansuli SUB-1) and resistant check (Sabitri) were tested. The field experiment was laid out in a randomized complete block design with three replications. Brown spot disease assessment was done based on the percent of leaf area diseased according to the 0-9 scales of the standard evaluation system. The percent disease severity was recorded at 50, 60, 70, and 80 days after transplanting (DAT). It was observed that the disease severity increased with an increase in the age of the crop from 50-80 DAT. Disease severity and the total AUDPC values were highly significant among the rice genotypes. Disease severity and total AUDPC value ranged from 28.52% to 39.42% and 853.33 to 1185.19 respectively. None of these genotypes was found either resistant or highly resistant to disease. The mean severity and total AUDPC values of the compared genotypes were significantly lower than Sabha Mansuli SUB-1. The Genotypes NR2181-465-1-1-1-1, NR2264-4-1-6-5, NR2215-6-4-2-2-2, NR2191-22-1-4-1-1, and NR2191-236-3-1-3-1 demonstrated mean severity and total AUDPC in increasing order but lesser than that of Sabitri. NR2181-465-1-1-1-1 had the lowest disease severity (28.52%) as well as total AUDPC value (853.33). From this experiment, it can be concluded that under similar field conditions, NR2181-465-1-1-1-1 genotype having lower mean disease severity and total AUDPC can be used for further multi location trials for resistance evaluation.