Different capability of native and non-native plant growth-promoting bacteria to improve snap bean tolerance to ozone.
The air pollutant ozone (O3) is a phytotoxic oxidative stressor, leading to visible foliar injury and plant growth decline. Plant growth-promoting bacteria (PGPB) are emerging as an eco-friendly tool for improving plant growth under stress. In order to test PGPB as a tool for alleviating O3 stress in plants, an O3 sensitive genotype (Phaseolus vulgaris L. cv S156) was inoculated with native (rhizobacterial; B1 and B2) and non-native PGPB (Bacillus megaterium and B. amylolequefaciens) and exposed to realistic O3 exposure (ambient, AA with AOT40 = 0.53 ppm per hour, and twice ambient ozone concentration, 2XAA, AOT40 = 1.84 ppm per hour). The promoting effect was assessed by quantifying visible foliar O3 injury (PII), chlorophyll a fluorescence (Fv/Fm), contents of hydrogen peroxide (H2O2), malondialdehyde (MDA) and nitric oxide (NO), ethylene emission, 1-aminocyclo-propane-1-carboxylate (ACC) deaminase enzyme activity, above- and below-ground biomass. BM, BA and B1 showed higher ACC deaminase enzyme activity and Fv/Fm, while ethylene emission, PII, H2O2, MDA and NO contents were lower in the BM, BA and B1 plants than in the B2 and non-inoculated plants under 2XAA. Only BA increased above- and below-ground biomass under AA and 2XAA. We conclude that PGPB are able to ameliorate O3 stress through induction of systemic resistance; the level of bacterial ACC deaminase is one of the good markers for identifying effective strains and may be tested as an agricultural practice for improving crop yield under O3 pollution.