Enhancement of Pathogen Resistance in Common Bean Plants by Inoculation With Rhizobium etli

Abstract

Symbiotic Rhizobium-legume associations are mediated by exchange of chemical signals that eventually result in the development of a nitrogen-fixing nodule. Such signal interactions are thought to be at the center of the plants’ capacity either to activate a defense response or to suppress the defense response to allow colonization by symbiotic bacteria. In addition, the colonization of plant roots by rhizobacteria activates an induced condition of improved defensive capacity in plants known as induced systemic resistance, based on “defense priming,” which protects unexposed plant tissues from biotic stress.Here, we demonstrate that inoculation of common bean plants with Rhizobium etli resulted in a robust resistance against Pseudomonas syringae pv. phaseolicola. Indeed, inoculation with R. etli was associated with a reduction in the lesion size caused by the pathogen and lower colony forming units compared to mock-inoculated plants. Activation of the induced resistance was associated with an accumulation of the reactive oxygen species superoxide anion (O2 −) and a faster and stronger callose deposition. Transcription of defense related genes in plants treated with R. etli exhibit a pattern that is typical of the priming response. In addition, R. etli–primed plants developed a transgenerational defense memory and could produce offspring that were more resistant to halo blight disease. R. etli is a rhizobacteria that could reduce the proliferation of the virulent strain P. syringae pv. phaseolicola in common bean plants and should be considered as a potentially beneficial and eco-friendly tool in plant disease management.

Immune Priming Triggers Cell Wall Remodeling and Increased Resistance to Halo Blight Disease in Common Bean

“…Alternative explanations for the Glc increase in the TFA fraction would be the accumulation of callose and/or the enrichment in a XG population tightly bound to cellulose. Both explanations seem plausible as the protective role of callose against Pph attack [ 86 ] and the function of XG by strengthening CW structure [ 63 , 64 ] have been previously reported. The CW fractionation of plants pre-treated with INA showed a noticeable displacement of matrix polysaccharides among fractions.…”

Induced systemic resistance -like responses elicited by rhizobia

“…Furthermore, to confirm that the defense response is systemic, the protective effect must be determined in organs different to those inoculated with rhizobia. These conditions are fulfilled in some of the works, confirming that rhizobia induce a defense response resembling ISR (Diaz-Valle et al 2019;Dutta et al 2008;Figueredo et al 2014Figueredo et al , 2017Figueredo et al , 2018. However, many others works were not originally designed with this aim and, therefore, fail to accomplish some of the requirements.…”

“…Many works provide data supporting the notion that inoculation of legumes with rhizobia results in the induction of an increased defense response effective against diverse pathogens (necrotrophs, biotrophs) and herbivores (Arfaoui et al 2005(Arfaoui et al , 2006(Arfaoui et al , 2007Chakraborty and Chakraborty 1989;Diaz-Valle et al 2019;Dutta et al 2008;Figueredo et al 2014Figueredo et al , 2017Kalantari et al 2018;Mabrouk et al 2007;Osdaghi et al 2011;Rabie 1998;Smigielski et al 2019) (Table 1). This effect was also observed in non legumes after rhizobial inoculation (Mishra et al 2006;Reitz et al 2000).…”

Competency of Rhizobial Inoculation in Sustainable Agricultural Production and Biocontrol of Plant Diseases

“…phaseoli significantly reduced the disease severity of CBB under both greenhouse and field experiments. Díaz-Valle et al (2019) delineated that the inoculation of common bean with Rhizobium etli inhibited halo blight severity as compared to plants not inoculated with the symbiont and indicated that the size of foliar pathogen lesion was 75% lesser in the Rhizobium etli-treated plants than in the uninoculated plants. Osdaghi et al (2011) assessed the inoculation of the Rhizobium leguminosarum bv.…”

“…viciae, Rhizobium meliloti, Rhizobium trifolii, Sinorhizobium meliloti, and Bradyrhizobium japonicum have been reported to produce antibiotics and cell-wall-degrading enzymes that can hinder the phytopathogenic bacteria (Gopalakrishnan et al, 2015). Díaz-Valle et al (2019) also showed that rhizobial inoculation facilitated greater and more rapid activation of defense-related genes following infection with the pathogenic bacteria and suggested that inoculation is imperative for a cellular mechanism of ISR in plants.…”