Effect of Pseudomonas spp. and Funneliformis mosseae on bacterial spot disease and growth response of pepper

The interaction of plant-growth promoting rhizobacteria (PGPR) and Arbuscular mycorrhizal fungi (AMF), used in biological control, could determine the outcome of the biocontrol of plant disease. The efficacy of AMF species (Funneliformi mosseae [Fm]) and PGPRs (Pseudomonas spp. V31Y4 and P. fluorescens WCS365) on pepper plant bacterial spot disease caused by Xanthomonas euvesicatoria (Xe) and host plant growth parameters were investigated. Bacteria biocontrol agents were suppressed significantly the disease severity, however Fm alone was not effective. Combination of Fm and WCS365 was the most successful treatment for disease suppression with a rate of 15% compared with the control. There was no significant difference among treatments with Xe induced defoliation. However, the number of leaves in plants inoculated with Fm and Xe decreased significantly compared with control plants. Nevertheless, single application of Fm and PGPRs significantly increased plant biomass, height and chlorophyll content, and the bacterial strains were more successful. The growth response (GR) value in plants ranged from 22 to 28.6% as a single or combination treatment without the disease pressure. However, under the disease pressure, this value changed from 3.6 to 20.9%. In disease-free conditions, V31Y4 treatment reduced Fm colonization, while WCS365 increased colonization. Conversely, under disease pressure, WCS365 treatment had no effect on Fm colonization while V31Y4 treatment increased it compared with the control. There was no significant relationship between phosphorus content and GR with disease severity.Finally, Fm application increased susceptibility to Xe in pepper plants, but the suitable PGPR and AMF combination treatment was more successful than single applications for disease suppression caused by Xe in pepper plants.