Interactive effects of Ag-nanoparticles, salicylic acid, and plant growth promoting rhizobacteria on the physiology of wheat infected with yellow rust

Abstract

The present investigation deals with the comparative study of plant growth promoting rhizobacteria (PGPR), salicylic acid (SA), and Ag-nanoparticle (AgNPs) on the physiology, sugar metabolism and yield of two varieties of wheat V-1 (GA 2002) and V-2 (Inqalab-91), differing in sensitivity to yellow rust. The study was based on the hypothesis that bacteria from stressed habitat may have better biocontrol potential than that of the normal condition. Three PGPR strains Bacillus cereus, Bacillus spp., and Burkholderia sp. were used as bioinoculant. The former two were isolated from the rhizosphere of wheat previously infected with rust and powdery mildew respectively and Burkholderia sp. was isolated from the rhizosphere of uninfected wheat. The seeds were soaked for 2 h prior to sowing in the broth culture of PGPR strains and SA. The AgNPs were applied as foliar spray (60 days after sowing). Yellow rust was induced 68 days after sowing. The treatments with Bacillus cereus, AgNPs, and SA effectively reduced the yellow rust in wheat as measured by AUDPC (area under production curve). Bacillus cereus significantly stimulated phenylalanine ammonia lyase activity. The abscisic acid (ABA), SA, indole acetic acid (IAA), and gibberellin (GA), the chlorophyll, and carotenoids contents were also increased in the sensitive variety (infected with yellow rust) following PGPR application. PGPR further augmented the activities of antioxidant enzymes and proline content. The biological yield was significantly higher in plants inoculated with Bacillus cereus. Bacillus cereus appears to act synergistically with SA to increase grain size. The tolerance to yellow rust is mediated by increase in the activity of phenylalanine ammonia lyase (PAL) and superoxide dismutase (SOD) and ABA content. AgNPs delay maturity and have a greater impact on the accumulation of photosynthates. Bacillus cereus can act synergistically with SA to improve total sugar content of flag leaves + grain. The AgNPs can be supplemented with Bacillus cereus for enhanced sugar production and sugar translocation to grains. AgNps and Bacillus cereus exhibit similar biocontrol potential against yellow rust as evidenced by AUDPC and PAL activity, but the Bacillus cereus superseded on AgNPs with respect to production of phytohormones, effect being more pronounced in the sensitive variety Inqalab-91.