Plant growth promoting rhizobacteria and their potential for biocontrol of phytopathogens

Abstract

Growth promotion and disease control by rhizobacteria are complex interrelated processes that involve direct and indirect mechanisms. The mechanisms include synthesis of some metabolites (auxin, cytokinin and gibberellins), induction of 1-aminocyclopropane-1-carboxylate (ACC) deaminase, production of siderophore, antibiotics, hydrogen cyanide hydrogen cyanide (HCN) and volatile compounds. They also include mineral solubilization competition, and induction of systemic resistance. These bacteria are suitable as soil inoculants because they have the potential for rapid and aggressive colonization. This feature alone is characterised as a disease control mechanism, which prevents the invasion of detrimental soil microorganisms onto the root surface. Inoculant-based plant growthpromoting rhizobacteria (PGPR) is applied extensively on agricultural crops to improve plants' growth and simultaneously reduce chemical inputs like fertilizer and pesticide which can cause environmental degradation. The structure of the rhizobacterial community is affected by several factors including plant genotype and is determined by the amount and composition of root exudates. In addition, soil type and fertility are the contributing factors that shape the community. This form of communication can affect plants' growth, nutrient status and also susceptibility to stress and pathogens in the host plant. PGPR inoculants cause diverse beneficial interactions among plants, which leads to sustainable and environment-friendly agriculture. The application of rhizosphere soil of agricultural crops with desirable bacterial populations is considered promising in both laboratory and greenhouse experiment. Further, a clearer understanding of the way PGPRs promote plants' growth can lead to expanded exploitation of these 'biofertilizers' in order to reduce the potential negative environmental effects associated with food and fiber production.

Insight Into the Role of PGPR in Sustainable Agriculture and Environment

“…Antibiotics produced by PGPR are more efficient than others due to their antimicrobial, insecticidal, antiviral, phytotoxic, cytotoxic, and anthelminthic properties (Fernando et al, 2018). Numerous species of Pseudomonas produce a wide scope of antifungal antibiotics, including 2,4-diacetylphloroglucinol (2,4-DAPG), butyrolactones, rhamnolipids, N-butylbenzene sulfonamide (Ramadan et al, 2016). Bacillus species also excrete a large variety of antibiotics, including bacilysin, bacillaene, mycobacillin, etc.…”

“…As the fungal cell wall is mostly made out of chitin and β−1,4-N-acetyl-glucosamine, Chitinase and β-1,3-glucanase of rhizobacteria can degrade them and act as are strong antifungals. For instance, P. fluorescens LPK2 and S. fredii KCC5 discharge β-glucanases and chitinases help in under-expression of the wilts which is brought about by Fusarium udum and F. oxysporum (Ramadan et al, 2016). Microbes show insecticidal action which has been accounted for protease, lipase, and chitinolytic activity (Rakshiya et al, 2016).…”

Prospect and Challenges for Sustainable Management of Climate Change-Associated Stresses to Soil and Plant Health by Beneficial Rhizobacteria

“…Additionally, protective enzymes are produced by the PGPRs to damage the cell walls of pathogenic organisms [172]. The β-1,3 glucanase and chitinase produced by P. fluorescens and Sinorhizobium fredii can break down the chitin and N-acetylglucoseamine of the fungal cell wall and thus control fungal diseases caused by F. oxysporum and F. udum [173]. It is also an effective and quick method to control plant pathogens.…”

Legume Biofortification and the Role of Plant Growth-Promoting Bacteria in a Sustainable Agricultural Era

“…There is a special type of bacteria, the PGPB, which includes either free-living bacteria or those that establish symbiotic relationships with plants in the rhizosphere or via endophytic colonization [64], that are very promising to be used in plant-based biofortification programs for the nutritional improvement of food crops. Plant growth promotion can be achieved by a series of mechanisms that can be direct: N fixation [65], nutrient (Fe, K, P, and Zn) solubilization [66,67], production of several phytohormones (auxins, cytokinins, gibberellins, ethylene, and abscisic acid) [68][69][70], and production of siderophores and organic acids [19,71,72], or indirect: biocontrol activity through Fe chelation, induced resistance, production of antibiotic, extracellular enzymes and cyanide, and competition for niches in the rhizosphere [73,74]. This promotion involves a series of bacterial components that act in very specific ways.…”