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 growth-promoting 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. Key words: Rhizobacteria, plant growth-promoting rhizobacteria (PGPR), root microbione, phytohormones, biocontrol, soil-borne phytopathgen, fluorescent pseudomonads.
Highlights
Members of the genus Pseudomonas are rod-shaped Gram-negative bacteria that are characterized by metabolic versatility, aerobic respiration, motility owing to one or several polar flagella, and a high genomic G+C content (59–68%)
They 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
Examples of some widely reported P solubilising microbial species intimately associated with a large number of agricultural crops like potato, tomato, wheat, radish, pulses etc., are Azotobacter chroococcum, Bacillus circulans and Cladosporium herbarum (Singh and Kapoor, 1999), B. japonicum (Antoun et al, 1998), Enterobacter agglomerans (Kim et al, 1998), Pseudomonas chlororaphis and P. putida (Cattelan et al, 1999) and Rhizobium leguminosarum (Chabot et al, 1998).The ability of plant growthpromoting rhizobacteria (PGPR) to solubilize mineral phosphate, has been of immense interest to agricultural microbiologists since it can enhance the availability of phosphorus for effective plant growth
Summary
Plant growth promoting rhizobacteria and their potential for biocontrol of phytopathogens Elshahat M. 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 include mineral solubilization competition, and induction of systemic resistance. 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. Soil type and fertility are the contributing factors that shape the community This form of communication can affect plants’ growth, nutrient status and susceptibility to stress and pathogens in the host plant.
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