Asian Journal of Microbiology and Biotechnology

Indian mustard (Brassica juncea L.) is an important oilseed crop grown in India, but its productivity is constrained by foliar diseases, including Alternaria blight caused by Alternaria brassicae and Alternaria brassicicicola. The symptoms of the disease appear as black spots on the underside of the leaves, which gradually enlarge to form concentric rings on the surface of the leaves. At a later stage, symptoms also appear on the stems and siliquae of the plant, which cause discoloration of seeds and early ripening of the pods, resulting in immature and infected seed yield. In view of the seriousness of the following disease, a survey on the incidence of Alternaria blight in Indian mustard was carried out in eastern Bihar during the 2023–2024 and 2024–2025 rabi seasons. Thirty sites were surveyed across Banka, Bhagalpur, Katihar, Khagaria, Madhepura and Munger, with five sites examined in each district to check the availability of the pathogen. For the study, disease samples were collected, isolated and incubated at room temperature to check the presence of Alternaria brassicicola. They were further examined using cultural and microscopic characteristics. The percentage disease incidence was also calculated to demonstrate the disease incidence on the crop under field conditions. Symptoms were recorded at all surveyed sites. Mean district incidence was 41.11% in Banka, 42.21% in Bhagalpur, 20.30% in Katihar, 56.90% in Khagaria, 61.39% in Madhepura and 63.81% in Munger, with an overall mean of 47.62%. Alternaria brassicicola was recovered from every site in both seasons, whereas Curvularia lunata was co-isolated from five sites in the first season and six sites in the second. The ratios of samples yielding A. brassicicola alone to those yielding both fungi were 5:1 and 4:1, respectively, indicating the dominance of Alternaria brassicicola. The findings indicate widespread recovery of A. brassicicola and marked spatial variation in disease incidence, providing baseline information on the distribution and incidence of Alternaria blight in eastern Bihar, which will be valuable for future epidemiological studies, resistance screening, and the formulation of region-specific disease management practices.