Comprehensive insights into sorghum (Sorghum bicolor) defense mechanisms unveiled: Plant growth-promoting rhizobacteria in combating Burkholderia-induced bacterial leaf stripe disease

Abstract

Sorghum, a vital cereal crop with significant importance in traditional human health systems, faces severe challenges from biotic stresses. This study aimed to assess the morpho-physiological variations and plant growth promoting rhizobacteria (PGPR)-induced defense mechanisms in sorghum against Burkholderia sp. infection, a well-known cause of bacterial leaf stripe disease. Also, the alterations in the leaf protein band profile of sorghum exposed to Burkholderia infection were assessed via 2-D gel electrophoresis wherein the disappearance of protein bands in diseased leaf tissues was recorded. The selected PGPR, A. chroococcum Beijerinck 1901 (MCC 2351), B. megaterium (MCC 2336), and P. fluorescens (NAIMCC B-00,340), secreted hydrogen cyanide and ammonia, and produced lytic enzymes, cellulase and amylase. When tested in-planta, Burkholderia sp., applied as a foliar spray, more profoundly impacted the growth as compared to seed coat application, resulting in significant reductions in root dry biomass, whole plant length, and total chlorophyll content by 93.9, 73.4 and 53.8 %, respectively, compared to disease-free control. Visible symptoms of bacterial leaf stripe disease like brown discoloration and necrotic lesions were observed in infected sorghum plants. Furthermore, the level of phytochemicals, proline, and malondialdehyde and antioxidants, CAT and SOD, in foliage declined significantly by 46.4, 70.2, 20.7, and 16.9 %, respectively, following inoculation with Bacillus applied as a seed coat. Additionally, Burkholderia-infected plants exhibited cellular damage, mainly in leaf tissues, as revealed by SEM and CLSM. Interestingly, the PGPR inoculation substantially enhanced the measured growth parameters of sorghum while reducing the levels of phytochemicals and antioxidants. These findings suggest that A. chroococcum, B. megaterium, and P. fluorescens, possessing biocontrol activity, can be employed as a profitable, environment and pocket-friendly approach for managing plant diseases and promoting the production of sorghum under biotic stress, thereby sufficing the human food demands.