Nematicidal effect of rhizobacteria on plant-parasitic nematodes associated with vineyards.

The action of metabolites and exoenzymes from rhizobacteria on different plant-parasitic nematodes has an influence on the nematicidal efficacy of the microbe. Seven rhizobacteria, divided into two bacterial groups, were evaluated in vitro for nematicidal activity on Meloidogyne ethiopica and Xiphinema index. The direct effect of their filtrates on egg hatching and juveniles of M. ethiopica as well as mobile stages of X. index was evaluated during a 72-h period. The production of four exoenzymes and two metabolites associated with nematode mortality was investigated. Molecular characterization of three isolates was performed, and the physiological profiles and lipase activity of all isolates were obtained using the BIOLOG EcoPlate system. While chitinase and collagenase were measured using the BIOLOG MT2 plate system, protease, hydrogen cyanide and hydrogen sulphide were directly determined in Petri dishes. Nematode mobile stages exposure to the bacterial filtrate revealed a nematicidal effect up to 93.7% on X. Index and up to 83.3% on M. ethiopica. The control of egg hatching varied between 35 and 85%. A positive correlation was found between the mortality of both nematode mobile stages and the concerted activities of the bacterial enzymes as well as the level of the volatile metabolites. The nematicidal effect of rhizobacteria strains varies by nematode genera and among the developmental stages evaluated.

Rhizobacteria with nematicide aptitude: enzymes and compounds associated.

The use of rhizobacteria to control plant parasitic nematodes has been widely studied. Currently, the research focuses on bacteria-nematode interactions that can mitigate this complex microbiome in agriculture. Various enzymes, toxins and metabolic by-products from rhizobacteria antagonize plant parasitic nematodes, and many different modes of action have been proposed. Hydrolytic enzymes, primarily proteases, collagenases and chitinases, have been related to the nematicide effect in rhizobacteria, proving to be an important factor involved in the degradation of different chemical constituents of nematodes at distinct developmental stages. Exuded metabolites may also alter the nematode-plant recognition process or create a hostile environment for nematodes in the rhizosphere. Specific bacteria strains responsible for the production of toxins, such as Cry proteins, are one of the strategies used by rhizobacteria. Characterization of the rhizobacteria mode of action could strengthen the development of commercial products to control populations of plant parasitic nematodes. This review aims to provide an overview of different enzymes and compounds produced by rhizobacteria related to the process of antagonism to plant-parasitic nematodes.

Exoenzymes and metabolites related to the nematicidal effect of rhizobacteria on Xiphinema index Thorne & Allen.

AIMS: To identify enzymes and metabolites in the rhizobacteria filtrates that have a nematicidal effect on Xiphinema index and perform molecular characterization of the strains evaluated. METHODS AND RESULTS: A series of four bacteria selected for their nematicidal potential were considered for in vitro, biochemical and molecular studies. The direct effect of the bacterial filtrates was evaluated in vitro on X. index juveniles and adults. Hydrogen sulphide and hydrogen cyanide liberation and protease, chitinase, collagenase and lipase activity were verified in the strains. Up to five housekeeping genes and one ITS 16S-23S rRNA were analysed. All bacterial filtrates presented 54-100% mortality when evaluated during up to 72 h of nematode exposure. Strains presented protease activity; two of them (strains FB833T and FR203A) showed reliable collagenase and chitinase activities, respectively, and three of them showed strong lipolytic activity (FB833T, FR203A and FS213P). Strain Bacillus megaterium FB133M had no lipase activity and presented the lowest nematicidal effect. Bacillus amyloliquefaciens FR203A had the largest lethal effect. CONCLUSION: The rhizobacteria strains evaluated in this study possess nematicidal compounds, which may offer an interesting alternative for X. index control. SIGNIFICANCE AND IMPACT OF THE STUDY: This is the first report of exoenzymes and metabolites associated with nematicidal effect of rhizobacteria on X. index, which can be a possible alternative for control of this plant-parasitic nematode.