Abstract
The present study demonstrates plant growth promotion and induction of systemic resistance in pea (Pisum sativum) plant against Fusarium oxysporum f.sp. pisi by two bacterial endophytes, Pseudomonas aeruginosa OS_12 and Aneurinibacillus aneurinilyticus OS_25 isolated from leaves of Ocimum sanctum Linn. The endophytes were evaluated for their antagonistic potential against three phytopathogens Rhizoctonia solani, F. oxysporum f. sp. pisi, and Pythium aphanidermatum by dual culture assay. Maximum inhibition of F. oxysporum f. sp. pisi was observed by strains OS_12 and OS_25 among all root rot pathogens. Scanning electron microscopy of dual culture indicated hyphal distortion and destruction in the case of F. oxysporum f. sp. pisi. Further, volatile organic compounds (VOCs) were identified by gas chromatography–mass spectrometry (GC-MS). The GC-MS detected eight bioactive compounds from hexane extracts for instance, Dodecanoic acid, Tetra decanoic acid, L-ascorbic acid, Trans-13-Octadecanoic acid, Octadecanoic acid. Both the endophytes exhibited multifarious plant growth promoting traits such as indole acetic production (30–33 μg IAA ml–1), phosphate solubilization, and siderophore and ammonia production. Pot trials were conducted to assess the efficacy of endophytes in field conditions. A significant reduction in disease mortality rate and enhancement of growth parameters was observed in pea plants treated with consortium of endophytes OS_12 and OS_25 challenged with F. oxysporum f.sp. pisi infection. The endophytic strains elicited induced systemic resistance (ISR) in pathogen challenged pea plants by enhancing activities of Phenylalanine ammonia lyase (PAL), peroxidase (PO), polyphenol oxidase (PPO), ascorbate oxidase (AO), catalase (CAT) and total phenolic content. The endophytes reduced the oxidative stress as revealed by decrease in malondialdehyde (MDA) content and subsequently, lipid peroxidation in host plant leaves. Robust root colonization of pea seedlings by endophytes was observed by scanning electron microscopy (SEM) and fluorescence microscopy. Thus, plant growth promoting endophytic P. aeruginosa and A. aneurinilyticus can be further exploited through bio-formulations for sustainable protection of crops against root rot diseases as bio-control agents.
Highlights
The conventional agricultural practices heavily rely on bulk use of chemical fertilizers and pesticides resulting in environmental pollution and deterioration of soil and human health
A total of 25 morphologically distinct bacterial endophytes were isolated from leaves of O. sanctum Linn. plants and purified by subculturing the isolates
No bacterial growth was observed in control plates which indicate the effectiveness of surface sterilization protocol and the selected bacterial isolates were considered as leaves endophytes
Summary
The conventional agricultural practices heavily rely on bulk use of chemical fertilizers and pesticides resulting in environmental pollution and deterioration of soil and human health. Plantmicrobe interactions are one of the most widely studied phenomena offering huge possibilities to design a tailormade formulations of microbes as a substitute to chemical inputs in enhancing plant growth and development In this regard, the use of plant-associated microbiota, collectively known as endophytes, represents a reliable and sustainable farming approach for plant growth as well as phytopathogen growth suppression and disease control. There are numerous studies demonstrating the immense potential of endophytes in plant growth promotion, stimulation of stress tolerance, suppression of plant pathogenic diseases, and alleviation of negative effects manifested upon biotic and abiotic stressed conditions through various direct and indirect mechanisms (Etminani and Harighi, 2018; Aeron et al, 2020; Kushwaha et al, 2020) These mechanisms include nitrogen fixation, plant growth hormone (auxins, cytokinin, and gibberellins) production, solubilization of phosphates and sequestration of iron by production of siderophores, production of antimicrobial bioactive metabolites, and competition for nutrients and ecological niches (Latha et al, 2019)
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