Elicitation of native bio protective microbial agents associated systemic defense responses and plant growth promotion against bacterial stalk rot pathogen in sorghum (Sorghum bicolor)

Abstract

Dickeya dadantii is the causal agent of bacterial stalk rot and one of the most destructive and widespread diseases of the sorghum in the world. Here, we explored microbe-based approaches for managing this destructive pathogen, intending to provide alternatives for integrated disease management. The objective of the research was to decipher the effect of antagonistic microbes on systemic defense enzymes, histochemical changes, plant growth attributes, reduction in disease severity, and interaction of these antagonistic microbes with host. Trichoderma, Pseudomonas, and Bacillus isolates were collected from rhizospheric soil and characterized using morphological and molecular tools. ITS and 16S rRNA sequences were analyzed to determine the molecular characterization of all antagonist microbes, and they were identified as T. asperellum, T. viride, T. harzianum, B. subtilis, and P. flourescens. These isolates were evaluated for antibacterial properties against D. dadantii under in vitro conditions and showed the higher inhibition in a dual culture method. Further, the effects of seed bio-priming and soil application of these isolates were tested under glasshouse and field conditions. T. viride outperformed the other isolates, significantly enhancing the plant growth parameters and induced resistance to Dickeya dadantii (BSR). T. viride showed a significantly higher accumulation of defensive enzymes, viz. PAL (1.02), PO (1.70), PPO (1.25), CAT (1.11), and TPC (0.91) at 48 h after pathogen challenge, as compared to the control. Histochemical tests confirmed lignification and callose deposition in the cell walls of the treated plants. Antagonist microbes were further evaluated under field conditions against D. dadantii infection. Compared to the control, there is a significant enhancement of plant growth parameters and yield with a simultaneous decrease in disease severity in T. viride treated plants. Results showed that the potential benefits of T. viride could not only effectively induce resistance in plants, enhance plant growth, increase yield, and suppress pathogen infection but also reduce the use of hazardous pesticides. As a result of correlation, PCA and heat map analyses indicated that T. viride is interconnected to determine the crop ability to sustain its growth under pathogen stress.