Virulence profiling of emerging Indian strains of Burkholderia glumae causing panicle blight of rice

Bacterial panicle blight (BPB), incited by Burkholderia glumae, has impacted rice production globally. Despite its significance, little is known about the disease and the virulence pattern of the causal agent. BPB is a major challenge in the rice-growing belts of North-western India. We have characterized the 21 BG strains using the 16S rRNA and the gyrB gene-based sequence approach in the present study. The gyrB gene-based phylogenetic analysis resulted in geographic region-specific clustering of the BG isolates into three clades. The BG isolates from Delhi-National Capital Region (Delhi NCR) (Clade 1) and Uttar Pradesh (UP) (Clade 2) were separated into two clades and the BG isolates from Uttarakhand and Haryana clustered together in a single clade (Clade 3). Likewise, we sequenced the eight major virulence-associated genes viz., toxA, toxB, lipA, lipB, pehA, pehB, flhC and flhD present across the genome of B. glumae and identified their interacting proteins through STRING analysis. Furthermore, virulence screening of 21 BG strains revealed the variation in the percentage of grains infected and the yield of rice plants. The most virulent BG1 strain resulted in the highest disease incidence (82.11%) and lowest yield (11.12 g/plant) and BG10 came out as the least virulent strain. Besides, the inoculation at three stages of the plant revealed that the booting stage of rice is the most susceptible stage which resulted in maximum disease percentage and less yield. Overall, our study gives information about virulence-associated gene characterization and variation in the virulence nature of Indian BG strains.