Assessing the Impact of Brown Spot Disease on Seed Health, Quality and Transmission in Paddy

Abstract

Brown spot disease, caused by Bipolaris oryzae, poses a significant threat to rice production, affecting both yield and quality. The present study aimed to investigate the major mycoflora associated with seeds of 11 paddy varieties and the effects of B. oryzae on seed health and quality, encompassing morphological characterisation, location and transmission studies and assessing seed infection under hydropriming and pregermination conditions. The results revealed that the major fungi associated with paddy seeds were B. oryzae, Aspergillus spp., Fusarium sp., Curvularia sp., Trichoconiella padwickii and Rhizopus sp. Among these, B. oryzae was the predominant fungus observed in all 11 rice varieties with the maximum seed infection. Studies on the cultural and morphological variations among the 11 isolates from B. oryzae revealed that they had diverse colony colour, growth patterns and conidial characteristics. Brown spot diseased seeds showed a substantial decline in germination (%) and seedling vigour with ADT (Aduthurai) 46 rice variety showing highest reduction in germination (47%), followed by ADT 42 (54%) compared to healthy seeds. Furthermore, brown spot infection was prevalent across all seed components tested—lemma, palea, endosperm and embryo at varying rates—, highlighting the comprehensive nature of the disease's impact on the seed structure. Disease progression studies using different methods revealed varying infection rates, with the test tube agar method demonstrating the highest assessment rates (44%–65%), followed by the blotter method (40%–46%) and sand method (18%–38%). Furthermore, lower brown spot pathogen infection from the seedling emerged after 30 days of sowing and was observed when diseased seeds were exposed to hydropriming conditions compared to pregerminated and untreated conditions. This study sheds light on the intricate dynamics of brown spot disease in rice which has negative impact on seed health, germination rate and, ultimately, rice productivity and quality.