Bio-priming with Brevibacterium frigoritolerans and Foliar Phytohormones Boost Plant Growth, Photosynthesis, and Antioxidant Mechanisms in Barley under Drought Stress

Abstract

Using plant growth-promoting bacteria (PGPB) or exogenous plant growth promoters, i.e., salicylic acid (SA) and gibberellic acid (GA), is an effective strategy for stress management in plants. A few publications have reported that Brevibacterium frigoritolerans has some superior characteristics in the mitigation of biotic and abiotic stresses in plants. Here we report the action of B. frigoritolerans on plant growth, photosynthesis, drought stress, and antioxidant defense system in barley with or without SA and GA treatments. According to the results, the rate of increase was 20.2% at root dry weight, 2.8% at root length, 8.7% at plant height, 248% at SOD, 309% at APX, 234% at CAT, and 20.8% at TSP in Tarm-92 compared with Zeynel A & gbreve;a. Root fresh weight, shoot fresh weight, shoot dry weight, plant height, and total chlorophyll content decreased at 25% FC (field capacity) by 34%, 41%, 54%, 15% and 16%, respectively. In addition, high drought stress (25% FC) increased SOD, APX, CAT, MDA, and total soluble protein (TSP) by 140%, 215%, 417%, 198% and 151%, respectively. Control plants exhibited the lowest enzymatic antioxidants and TSP, while they had the highest MDA concentrations in plants. The highest SOD (2001 ng mL-1), APX (8.83 ng mL-1), and CAT (29.08 ng mL-1) were determined with PGPB+GA, PGPB, and GA-treated plants, respectively. On the other hand, the lowest MDA (15.77 ng mL-1) was observed in PGPB+SA+GA-treated plants. In conclusion, foliar application of 1.5 mM SA or 110 mg L-1 GA with B. frigoritolerans bio-priming had the most mitigating action on drought stress in barley.