District-wise Distribution and Severity of Bacterial Leaf Blight of Rice Caused by Xanthomonas oryzae pv. oryzae in Northern Karnataka, India

Abstract

Bacterial leaf blight (BLB), caused by Xanthomonas oryzae pv. oryzae, is one of the most destructive diseases affecting rice production in India, particularly under favourable agro-climatic conditions. A roving field survey was conducted during kharif 2023 and kharif 2024 to assess the severity and spatial distribution of BLB in major rice-growing districts of northern Karnataka, namely Dharwad, Belagavi, and Haveri. Disease severity was recorded using the Standard Evaluation System scale and expressed as per cent disease index (PDI). The survey revealed considerable spatial and temporal variation in BLB severity across districts, taluks, villages, crop growth stages, soil types, and rice genotypes. During kharif 2023, mean PDI values were higher, with Belagavi recording a PDI of 14.67 per cent, followed by Dharwad (PDI 14.33 %) and Haveri (13.64 %). In kharif 2024, a decline in disease severity was observed, with Dharwad recordinga PDI of 12.00 per cent, Haveri 10.68 per cent, and Belagavi 10.34 per cent, indicating seasonal variation in disease intensity. Genotype-wise analysis based on pooled data showed marked differences in BLB severity, reflecting variability in host response under field conditions. Disease incidence was influenced by factors such as soil moisture retention, irrigation status, crop stage, and varietal susceptibility. The study highlights the continued importance of BLB as a constraint to rice productivity in northern Karnataka and underscores the need for regular surveillance, deployment of tolerant or resistant varieties, and location-specific disease management strategies. The baseline information generated will be useful for resistance breeding, epidemiological studies, and disease forecasting in the region.