Harnessing plant growth-promoting bacteria to combat watermelon mosaic virus in squash.

Plant diseases significantly threaten global food security, with viral infections, particularly Watermelon Mosaic Virus (WMV), causing substantial losses in economically important crops such as squash. This study aims to investigate the efficacy of beneficial bacteria isolated from various plants in promoting growth and mitigating the effects of WMV in squash. Understanding the interactions between plants and beneficial microbes could provide sustainable solutions for managing viral infections in agriculture. Sixty-two bacterial isolates were obtained from the rhizosphere of basil, mint, thyme, and squash plants. Among these, six strains exhibited notable plant growth-promoting activities, including the synthesis of indole acetic acid, solubilization of phosphate and zinc, ammonia production, and activity of 1-aminocyclopropane-1-carboxylate deaminase (ACCD). Morphological observations and 16S rRNA gene sequencing identified these isolates as Pseudomonas indica, Bacillus paramycoides, Bacillus thuringiensis, Bacillus mycoides, Paenibacillus glucanolyticus, and Niallia circulans. In pot experiments, squash plants inoculated with these bacterial strains demonstrated significant reductions in disease severity after being infected with WMV. Specifically, foliar applications of the bacteria resulted in the following reductions in disease severity: B. mycoides (87%), B. thuringiensis (73%), Paenibacillus glucanolyticus (73%), Niallia circulans (70%), B. paramycoides (65%), and Pseudomonas indica (65%). Additionally, plants treated with B. mycoides showed increased plant height and shoot dry weight, indicating enhanced growth performance relative to infected controls. Statistical analysis revealed that these growth promotions and disease severity reduction were significant (p < 0.05). GC-MS analysis of the six bacterial strains revealed a diverse array of 73 chemical metabolites, including common compounds such as 9-Octadecenoic acid (Z), benzene derivatives, and cyclopentanones. These findings suggest shared metabolic pathways among the strains and indicate potential roles in ecological interactions, plant defense mechanisms, and antiviral properties. These metabolites likely contribute to the observed reductions in viral severity and enhance plant resilience. The study indicates that inoculating squash plants with specific beneficial bacteria, especially B. mycoides, through foliar or soil application can significantly decrease the severity of WMV and promote plant growth. This approach offers an environmentally friendly alternative to chemical antiviral treatments and may reduce reliance on pesticides. This research highlights the potential of using plant growth-promoting bacteria (PGPB)as a sustainable approach to control viral infections in crops. Further field trials are necessary to PGPB validate the scalability of these findings and assess their effectiveness under diverse agricultural conditions. Incorporating these beneficial microbes into agricultural practices could enhance the resilience of cropping systems, ultimately fostering sustainable agriculture and enhancing food security.