Applying phosphate-solubilizing bacteria (PSB) as biofertilizers has enormous potential for sustainable agriculture. Despite this, there is still a lack of information regarding the expression of key genes related to phosphate-solubilization (PS) and efficient formulation strategies. In this study, we investigated rock PS by Ochrobactrum sp. SSR (DSM 109610) by relating it to bacterial gene expression and searching for an efficient formulation. The quantitative PCR (qPCR) primers were designed for PS marker genes glucose dehydrogenase (gcd), pyrroloquinoline quinone biosynthesis protein C (pqqC), and phosphatase (pho). The SSR-inoculated soil supplemented with rock phosphate (RP) showed a 6-fold higher expression of pqqC and pho compared to inoculated soil without RP. Additionally, an increase in plant phosphorous (P) (2%), available soil P (4.7%), and alkaline phosphatase (6%) activity was observed in PSB-inoculated plants supplemented with RP. The root architecture improved by SSR, with higher root length, diameter, and volume. Ochrobactrum sp. SSR was further used to design bioformulations with two well-characterized PS, Enterobacter spp. DSM 109592 and DSM 109593, using the four organic amendments, biochar, compost, filter mud (FM), and humic acid. All four carrier materials maintained adequate survival and inoculum shelf life of the bacterium, as indicated by the field emission scanning electron microscopy analysis. The FM-based bioformulation was most efficacious and enhanced not only wheat grain yield (4–9%) but also seed P (9%). Moreover, FM-based bioformulation enhanced soil available P (8.5–11%) and phosphatase activity (4–5%). Positive correlations were observed between the PSB solubilization in the presence of different insoluble P sources, and soil available P, soil phosphatase activity, seed P content, and grain yield of the field grown inoculated wheat variety Faisalabad-2008, when di-ammonium phosphate fertilizer application was reduced by 20%. This study reports for the first time the marker gene expression of an inoculated PSB strain and provides a valuable groundwork to design field scale formulations that can maintain inoculum dynamics and increase its shelf life. This may constitute a step-change in the sustainable cultivation of wheat under the P-deficient soil conditions.
Global maize productivity has decreased due to sudden temperature fluctuations and heat waves. The current study demonstrates the potential of beneficial bacteria for evaluating plant heat tolerance during early growth. Three Bacillus spp. AH-08, AH-67, SH-16, and one Pseudomonas spp. SH-29 showed the ability to grow and exhibited multiple plant-beneficial traits up to 45 ± 2°C. In Bacillus sp. SH-16 two small heat shock proteins (HSP) of 15 and 30kDa and in SH-16 and AH-67 two large HSP of 65 and 100kDa were upregulated at 45 and 50°C. Plant-inoculation with the consortium B3P was carried out on six maize varieties pre-grown at 25 ± 2 ºC and then applied heat shock at 10-day for 3h at 38ºC, and then 48h at 42ºC. The B3P treatment showed significant improvement in the plant growth parameters and level of catalase, peroxidase, chlorophyll, and carotenoids. The expression of HSP1 and HSP18 in Malka and YH-5427 while HSP70 and HSP101 were higher in FH-1046 and Gohar as compared to control. The results indicate that PGPR exert multiphasic responses to improve plant growth and heat-tolerance during seedling growth. Further studies will be focused on the field evaluation of this consortium under high heat to evaluate the impact on crop yield.
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