Biological control of bacterial wilt of common bean by plant growth-promoting rhizobacteria

Abstract

Bacterial wilt (BW) caused by Curtobacterium flaccumfaciens pv. flaccumfaciens (Cff) is an emerging, seed-transmitted disease of common bean (Phaseolus vulgaris) in Brazil, and plant growth-promoting rhizobacteria (PGPR) have the potential to be used in disease management. The present work aimed at determining the potential of selected PGPR on the biological control of BW through seed treatment, growth promotion and induced resistance. Bean seeds cv. ‘Pérola’ were artificially inoculated with Cff, immersed in a PGPR suspension, and sown in 4 L pots containing a soil: sand mixture (2:1). Plants were assessed for seedling emergence (SE), speed emergence index (SEI), relative growth index (RGI), root dry weight (RDW), shoot dry weight (SDW), as well as biochemical plant responses in the presence or absence of Cff. The disease control ranged from 42% to 76%, respectively, for Bacillus subtilis UFLA285 and ALB629 compared to the untreated control. PGPR treatments also increased RGI, SDW, and RDW. Upon Cff inoculation, UFLA285 increased phenolics’ content and ALB629 in the lignin accumulation compared to the untreated control. Without the pathogen inoculation, both PGPR promoted an increase in phenylalanine ammonia lyase activity and total phenolics content and UFLA285 in the lignin accumulation. Our findings demonstrated the potential of selected PGPR for disease control, enhancement of the RGI and biomass accumulation. Surprisingly, instead of a priming effect of PGPR, Cff apparently blocks the defense response development although the overall phenotype is disease control, suggesting there is a complementary and/or compensatory mode of action involved.