Screening rice genotypes for brown spot resistance along with yield attributing characters and its association with morphological traits

Brown spot, caused by Bipolaris oryzae, is a devastating disease of rice which can cause yield loss in most rice-growing regions of the world. Breeding for disease resistance is the preferred strategy of managing brown spot. Hence, identification and subsequent development of disease resistance in rice genotypes are crucial. The field resistance of 95 rice genotypes to brown spot was evaluated under water and fertilizer stress during 2017 and 2018. Partial resistance was assessed through reaction type (disease rating) and epidemiological parameters estimates i.e. final brown spot index, area under disease progress curve and apparent infection rate. Disease rating, brown spot index, and area under disease progress curve detected differences in the responses of rice genotypes to disease under field condition, which could be used to study brown spot resistance. Among the genotypes tested, 22 genotypes were resistant to moderately resistant (23.16%) while majority were moderately susceptible to susceptible (76.84%). A significant correlation between leaf angle and area under disease progress curve indicated positive influence of leaf erectness on severity of brown spot disease. Results showed that leaf infection did not significantly affect the number of filled grains per panicle or hundred seed weight, but caused yield decline by decreasing the number of productive tillers. Nevertheless, the infection of rice genotypes from flowering to ripening stages decreased the number of filled grains per panicle and grain weight. The resistant genotypes identified in this study can be exploited for future rice breeding programs to develop promising resistant lines in management of the brown spot disease.