Bacillus licheniformis FMCH001 Increases Water Use Efficiency via Growth Stimulation in Both Normal and Drought Conditions

Abstract

Increasing agricultural losses due to biotic and abiotic stresses caused by climate change challenge food security worldwide. A promising strategy to sustain crop productivity under conditions of limited water availability is the use of plant growth promoting rhizobacteria (PGPR). Here, the effects of spore forming Bacillus licheniformis (FMCH001) on growth and physiology of maize (Zea mays L. cv. Ronaldinho) under well-watered and drought stressed conditions were investigated. Pot experiments were conducted in the automated high-throughput phenotyping platform PhenoLab and under greenhouse conditions. Results of the PhenoLab experiments showed that plants inoculated with B. licheniformis FMCH001 exhibited increased root dry weight (DW) and plant water use efficiency (WUE) compared to uninoculated plants. In greenhouse experiments, root and shoot DW significantly increased by more than 15% in inoculated plants compared to uninoculated control plants. Also, the WUE increased in FMCH001 plants up to 46% in both well-watered and drought stressed plants. Root and shoot activities of 11 carbohydrate and eight antioxidative enzymes were characterized in response to FMCH001 treatments. This showed a higher antioxidant activity of catalase (CAT) in roots of FMCH001 treated plants compared to uninoculated plants. The higher CAT activity was observed irrespective of the water regime. These findings show that seed coating with Gram positive spore forming B. licheniformis could be used as biostimulants for enhancing plant WUE under both normal and drought stress conditions.

Keywords: antioxidants; biostimulants; plant growth promoting rhizobacteria; plant probiotics; water use efficiency.

FIGURE 1

Schematic diagram showing the timeline of PhenoLab (P1–P3) and Greenhouse (G1–G2) experiments. Δ indicates destructive harvesting points. Black triangles denote harvest points in the end of treatments whereas gray triangles describe interim harvests. W 90% indicates well-watered treatment; D 65% indicates drought stress, D-R indicates the plants were exposed to drought stress and then re-watered. C indicates uninoculated control plants while FMCH001 indicates plants inoculated with seed coated Bacillus licheniformis sp. FMCH001.

FIGURE 2

Shoot dry weight (A), root dry weight (B), and root/shoot ratio (C) of inoculated and uninoculated maize grown in Greenhouse experiments during drought and recovery period. W 90% indicates well-watered treatment; D-R indicates drought stressed plants which were re-watered during recovery. C indicates uninoculated control plants while FMCH001 indicates plants inoculated with seed coated Bacillus licheniformis sp. FMCH001. Bars represent mean ± SE (n = 4). M indicates microbial inoculation, I indicates drought treatment, and I × M indicates interaction between drought and microbial inoculation. The output of two-way ANOVA is also included where ^∗ and ^∗∗ denote significantly different at P < 0.05 and P < 0.01 levels, respectively, ns indicates no significant difference. Different letters on top of columns denote significant differences within the treatment at P < 0.05.

FIGURE 3

Leaf relative water content (A), leaf water potential (B), and plant water use efficiency (C) of inoculated and uninoculated maize grown in Greenhouse experiments during drought and recovery period. W 90% indicates well-watered treatment; D-R indicates drought stressed plants which were re-watered during recovery. C indicates uninoculated control plants while FMCH001 indicates plants inoculated with seed coated Bacillus licheniformis sp. FMCH001. Bars represent mean ± SE (n = 4). M indicates microbial inoculation, I indicates drought treatment, and I × M indicates interaction between drought and microbial inoculation. The output of two-way ANOVA is also included where ^∗ and ^∗∗ denote significantly different at P < 0.05 and P < 0.01 levels, respectively, ns indicates no significant difference. Different letters on top of columns denote significant differences within the treatment at P < 0.05.