Effective and durable systemic wheat-induced resistance by a plant-growth-promoting rhizobacteria consortium of Paenibacillus sp. strain B2 and Arthrobacter spp. strain AA against Zymoseptoria tritici and drought stress

Abstract

For a sustainable environment, plant-growth-promoting rhizobacteria (PGPR) are natural resources considering as one of the most important fungicides’ alternatives inducing resistance to plant diseases.The aim of the present work is to investigate the synergistic promotion effect of a PGPR mixture composed of Paenibacillus sp. strain B2 (PB2) and Arthrobacter spp. strain AA (AA), referred hereafter as Mix-2, on the wheat growth, resistance to Zymoseptoria tritici (teleomorph Mycosphaerella graminicola), the causal agent of Septoria tritici blotch (STB) and drought stress.The results of the quantitative real-time polymerase chain reaction (qPCR) showed a helpful effect of AA for wheat-root external and internal colonization with PB2. Interestingly, in non-stress conditions, the inoculation of wheat grains with Mix-2 (PB2:AA, 1:1), at sowing, showed an increase in almost all tested cultivars for foliar and root dry biomasses. Under drought stress, contrarily to PB2 in single inoculation, Mix-2 induced a significant tolerance in all tested cultivars for plant dry biomass and root length. On the other hand, both PB2 alone and Mix-2 induced resistance against Z. tritici with at least 50% of protection efficiency in all tested cultivars. However, Mix-2-root colonization and -induced resistance were observed at the most mature wheat growth stage. Moreover, Mix-2-induced resistance is characterized by the upregulation of gene markers of the basal defense, defense and cell rescue, reactive oxygen species, jasmonic acid, and phenylpropanoids & phytoalexins pathways. Pathogenesis-related protein 1 (PR1), chitinase, glucanase, and flavonoides are possible gene markers for wheat resistance selection to STB.To conclude, the endophyte PGPR’ consortium of AA and PB2 is a wheat growth promoter and inducer of a durable-systemic resistance to Z. tritici and genotype-independent tolerance to drought stress.