Drought-tolerance of wheat improved by rhizosphere bacteria from harsh environments

Water is the key resource limiting world agricultural production. Although an impressive number of research reports have been published on plant drought tolerance enhancement via genetic modifications during the last few years, progress has been slower than expected. We suggest a feasible alternative strategy by application of rhizospheric bacteria coevolved with plant roots in harsh environments over millions of years, and harboring adaptive traits improving plant fitness under biotic and abiotic stresses. We show the effect of bacterial priming on wheat drought stress tolerance enhancement, resulting in up to 78% greater plant biomass and five-fold higher survivorship under severe drought. We monitored emissions of seven stress-related volatiles from bacterially-primed drought-stressed wheat seedlings, and demonstrated that three of these volatiles are likely promising candidates for a rapid non-invasive technique to assess crop drought stress and its mitigation in early phases of stress development. We conclude that gauging stress by elicited volatiles provides an effectual platform for rapid screening of potent bacterial strains and that priming with isolates of rhizospheric bacteria from harsh environments is a promising, novel way to improve plant water use efficiency. These new advancements importantly contribute towards solving food security issues in changing climates

Enhancement of wheat (<i>Triticum aestivum</i>) drought tolerance by <i>Bacillus thuringiensis</i> AZP2 and <i>Paenibacillus polymyxa</i> B in sand soil.

<p>Panel A demonstrates the effect of AZP2 and B priming on seedlings survival after a severe 10-day drought stress episode. Panel B shows the effect of AZP2 priming on whole plant dry mass after 8 days growth without watering. The statistical analysis in (A) is based on a three-way ANOVA (stress, strains (i.e. AZP2 and B) and stress exposure time). ANOVA was conducted on two plant groups with 16 replicates in each group. *** indicate highly significant effects for the tested factor at <i>P≤</i>0.01. In B, eight independent experiments were performed, and treatments labelled with the same letter are not significantly different at <i>P≤</i>0.01.</p

Effect of priming by <i>Bacillus thuringiensis</i> AZP2 on wheat <i>(Triticum aestivum L. cv. Stava)</i> on average (±SD) growth characteristics, water use efficiency and antioxidant enzyme activities.

1<p>Analysis of plant root was conducted by Root Reader3D Imaging and Analysis System and manually <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0096086#pone.0096086-Niinemets1" target="_blank">[7]</a>.</p>2<p>Twelve plants per treatment were sampled. Roots with adhering soil (RAS) were carefully separated from bulk soil by shaking. Soil and root dry mass (RT) was recorded after drying the samples at 105°C, and RAS/RT ratio was calculated.</p>3<p>Twelve plants were carefully separated from soil by shaking followed by washing the roots in distilled water and left to drain in Petri dishes with water to maintain humidity. Root system characteristics were evaluated by Zeiss LSM 710 microscope.</p>4<p>Water use efficiency is defined as the ratio of total plant dry mass per total water used.</p>5<p>MDHAR - Monodehydroascorbate reductase, GR- Glutathione reductase, SOD- Superoxide dismutase, CAT-Catalase.</p><p>See Materials and Methods for enzyme extraction and activity measurements.</p><p>*Means followed by the same letter are not significantly different at p≤0.01. See Experimental procedures.</p

Temporal variations in the emission rates of some benzenoids and terpenoids emitted by wheat plants.

<p>Benzaldehyde (A), β-pinene (B) and geranyl acetone (C) emission rates from leaves of drought-stressed (0, 2, 5, 8 and 10 days without water) wheat plants after priming with <i>Bacillus thuringiensis</i> AZP2 are demonstrated. The error bars indicate +SE for three biological replicates. Statistical analysis and levels of significance as in Fig. 4.</p

Net assimilation rate (A) and stomatal conductance (B) of <i>Bacillus thuringiensis</i> AZP2-primed wheat seedlings under drought stress.

<p>The data are shown for plants grown for 0, 2, 5, 8 and 10 days without water. The error bars indicate +SE for three biological replicates. Statistical analysis is based on three-way ANOVA with stress, strains (<i>Bacillus thuringiensis</i> AZP2 vs. <i>P. polymyxa</i> B) and stress exposure time as factors. ***, ** and ns, indicate highly significant, significant or non-significant effects for the tested factor at <i>P<</i>0.05.</p