Disease incidence and yield loss in rice due to grain discolouration

Grain discolouration is an emerging disease of rice that has potential to cause huge losses if favourable conditions are available. The disease is caused by a pathogen complex and was reported from few places of India. During rabi season in 2019, a survey was undertaken at the paddy fields of NRRI, Cuttack, and found heavy incidences of grain discolouration in the cultivated rice genotypes with symptoms in the form of brown-/black-/ash-coloured grains mostly accompanied with chaffiness. The grain discolouration incidence ranged from 25 to 92% in different rice genotypes. The high disease incidence may be due to abrupt climate change, thereby increasing the virulence of the once minor pathogen(s) to gain fitness and causing devastation in rice crop. The mean yield loss due to grain discolouration was 18.9% and ranged between 0.1 and 60.2%. All the rice genotypes examined were susceptible to the disease. However, yield loss was not very devastating because only few genotypes showed higher yield loss while the remaining genotypes have much lower values. During the investigation, the temperature ranging from 25 to 37 °C, moderate rainfall, high relative humidity of 70–76% and high wind speed were observed that played a critical role in the disease outbreak. Therefore, epidemiology and management of grain discolouration should be the current concerns in order to halt the disease from affecting rice production in the country.