Evaluation of commercial rhizobacteria-based bio-inoculants for the control of the false root-knot nematode Nacobbus aberrans sensu lato and the promotion of pepper plants

Abstract

Nacobbus sp. is a phytoparasitic nematode that affects economically important crops. Due to the negative environmental and health impacts of chemical nematicides, sustainable alternatives, such as the use of biological control agents, are being developed. Rhizobacteria are microorganisms that can suppress nematode reproduction by producing different metabolites, induce systemic resistance in plants and stimulate plant growth. The aim of this study was to investigate whether the inoculation with commercial formulations of plant-growth promoting rhizobacteria (PGPR) can mitigate the deleterious effects of the nematode N. aberrans s.l. and promote the growth of pepper plants grown in greenhouses under biotic stress. Different bacteria were tested in vitro before being inoculated into pepper plants. Plants were inoculated with Bacillus subtilis, Bacillus thuringiensis and Azospirillim brasilense at transplant and then every 15 days, in the presence and absence of N. aberrans s.l.. The pathogen reproduction factor was 5.34; 2.09; 0.88 and 12.46 for A. brasilense B. subtilis, B. thuringiensis and control, respectively. In both nematode-parasitized and unparasitized plants, the rhizobacteria increased the soluble proteins (54%) and chlorophyll (18%) content and exerted a positive effect on net photosynthesis, transpiration, stomatal conductance and increased water use efficiency, height, stem diameter, fresh and dry weight. This beneficial effect was also verified by a lower accumulation of proline and sugars, metabolites used by plants as osmoregulators in stress situations. These results showed that B. thuringiensis and B. subtilis perform better in promoting pepper growth in the presence of the nematode and in the biocontrol of this pathogen.