Induced resistance in tomato plants promoted by two endophytic bacilli against bacterial speck

Abstract

Endophytic bacteria Bacillus pumilus and Bacillus amyloliquefaciens, indigenous from tomato, were evaluated for their ability to induce resistance against bacterial speck in tomato plants. Plants grown from seeds that were bacterized with the two Bacillus species and inoculated with a green fluorescent protein-marked Pseudomonas syringae pv. tomato NS4 displayed reduced disease severity when compared to control treatment (water). However, plants in an induced state had a slight negative effect on plant growth parameters such as plant height and plant dry weight. Under epifluorescence microscopy, on tomato phylloplane of plants grown from seeds bacterized with the bacilli, the GFP-marked strain population was drastically reduced and presented individual cells or few aggregates of the pathogen between the depressions along the junctions on the leaf surface. In addition, peroxidase (POX), polyphenol oxidase (PPO) and phenylalanine ammonia-lyase (PAL) enzyme activities were evaluated in plant extracts, and all showed increased activity. We report the ability of two Bacillus species in promoting the phenomenon of induced resistance in tomato plants by a significant increase in POX, PPO and PAL activities, which produced a protective effect in reducing disease severity in levels that reached 62%.