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Colonization of exopolysaccharide-producing Paenibacillus polymyxa on peanut roots for enhancing resistance against crown rot disease
Abstract
The effect of Paenibacillus polymyxa (syn. Bacillus polymyxa) which produces an exopolysaccharide (EPS) on control of crown rot disease caused by Apergillus niger of peanut was investigated. In an in
vitro assay, two strains of P. polymyxa (B5 and B6) were tested against A. niger. Both strains showed inhibitory effect against A. niger. Growth, protein and biopolymers production of bacteria were evaluated. The biopolymers were purified with several precipitation steps using ethanol and cetyltrimethyl-ammonium bromide. Carbohydrate analysis using various color reactions, infrared spectroscopy, and high performance liquid chromatography (HPLC) revealed that the biopolymer is a
homopolysaccharide, which is consisting of various sugars such as glucose, galactose, mannose and xylose. When these strains of P. polymyxa were applied to seed and sowed in soil infested with A.
niger, they significantly suppressed crown rot disease development and decreased survival of the A. niger pathogen. Over a period of 60 days, the population of bacteria was greatly increased. The bacterium colonized plant roots and were able to migrate downward with the root as it elongated. Scanning electron microscopic analysis of one month plants from seeds previously inoculated with P.polymyxa revealed dense colonization on the roots. Moreover, significant increases in activities of plant defense enzymes include -1,3-glucanase and chitinase were recorded in treated roots compared with untreated. In vivo, two trials were conducted in 2005 and 2006 seasons to define the effect of bacterium treatment on crown rot disease control and pod yield. Plants grown from peanut seeds previously treated with P. polymyxa displayed significant resistance to the crown rot disease triggered by A. niger. Coating seeds with bacterium decreased infection by A. niger, Aspergillus counts in the rhizosphere, pods and seeds as well as increased root colonization with bacteria. The yield of bacterium-treated peanut plants was significantly higher than untreated control plants. These results showed that P.polymyxa is potentially a biocontrol agent for use in controlling of A. niger in roots and seeds of peanut plants.
vitro assay, two strains of P. polymyxa (B5 and B6) were tested against A. niger. Both strains showed inhibitory effect against A. niger. Growth, protein and biopolymers production of bacteria were evaluated. The biopolymers were purified with several precipitation steps using ethanol and cetyltrimethyl-ammonium bromide. Carbohydrate analysis using various color reactions, infrared spectroscopy, and high performance liquid chromatography (HPLC) revealed that the biopolymer is a
homopolysaccharide, which is consisting of various sugars such as glucose, galactose, mannose and xylose. When these strains of P. polymyxa were applied to seed and sowed in soil infested with A.
niger, they significantly suppressed crown rot disease development and decreased survival of the A. niger pathogen. Over a period of 60 days, the population of bacteria was greatly increased. The bacterium colonized plant roots and were able to migrate downward with the root as it elongated. Scanning electron microscopic analysis of one month plants from seeds previously inoculated with P.polymyxa revealed dense colonization on the roots. Moreover, significant increases in activities of plant defense enzymes include -1,3-glucanase and chitinase were recorded in treated roots compared with untreated. In vivo, two trials were conducted in 2005 and 2006 seasons to define the effect of bacterium treatment on crown rot disease control and pod yield. Plants grown from peanut seeds previously treated with P. polymyxa displayed significant resistance to the crown rot disease triggered by A. niger. Coating seeds with bacterium decreased infection by A. niger, Aspergillus counts in the rhizosphere, pods and seeds as well as increased root colonization with bacteria. The yield of bacterium-treated peanut plants was significantly higher than untreated control plants. These results showed that P.polymyxa is potentially a biocontrol agent for use in controlling of A. niger in roots and seeds of peanut plants.
