Differential Root Exudation and Architecture for Improved Growth of Wheat Mediated by Phosphate Solubilizing Bacteria

Abstract

Phosphorous (P) deficiency is a major challenge faced by global agriculture. Phosphate-solubilizing bacteria (PSB) provide a sustainable approach to supply available phosphates to plants with improved crop productivity through synergistic interaction with plant roots. The present study demonstrates an insight into this synergistic P-solubilizing mechanism of PSB isolated from rhizosphere soils of major wheat-growing agro-ecological zones of Pakistan. Seven isolates were the efficient P solubilizers based on in vitro P-solubilizing activity (233-365 μg ml–1) with a concomitant decrease in pH (up to 3.5) by the production of organic acids, predominantly acetic acid (∼182 μg ml–1) and gluconic acid (∼117 μg ml–1). Amplification and phylogenetic analysis of gcd, pqqE, and phy genes of Enterobacter sp. ZW32, Ochrobactrum sp. SSR, and Pantoea sp. S1 showed the potential of these PSB to release orthophosphate from recalcitrant forms of phosphorus. Principal component analysis indicates the inoculation response of PSB consortia on the differential composition of root exudation (amino acids, sugars, and organic acids) with subsequently modified root architecture of three wheat varieties grown hydroponically. Rhizoscanning showed a significant increase in root parameters, i.e., root tips, diameter, and surface area of PSB-inoculated plants as compared to uninoculated controls. Efficiency of PSB consortia was validated by significant increase in plant P and oxidative stress management under P-deficient conditions. Reactive oxygen species (ROS)-induced oxidative damages mainly indicated by elevated levels of malondialdehyde (MDA) and H2O2 contents were significantly reduced in inoculated plants by the production of antioxidant enzymes, i.e., superoxide dismutase, catalase, and peroxidase. Furthermore, the inoculation response of these PSB on respective wheat varieties grown in native soils under greenhouse conditions was positively correlated with improved plant growth and soil P contents. Additionally, grain yield (8%) and seed P (14%) were significantly increased in inoculated wheat plants with 20% reduced application of diammonium phosphate (DAP) fertilizer under net house conditions. Thus, PSB capable of such synergistic strategies can confer P biofortification in wheat by modulating root morphophysiology and root exudation and can alleviate oxidative stress under P deficit conditions.

Designing Synergistic Biostimulants Formulation Containing Autochthonous Phosphate-Solubilizing Bacteria for Sustainable Wheat Production

“…It is involved in oxidation and cyclization of 3 a -(2-amino-2-carboxy-ethyl)-4 and 5-dioxo hexahydoquinoline dicarboxylic acid in the final step of PQQ biosynthesis (Meyer et al, 2011 ). In our previous studies, we revealed gcd (accession numbers MK883706 ), pho (accession numbers MK883704 ; Rasul et al, 2021 ), and pqqE genes (accession numbers MT897167 ; Yahya et al, 2021 ) containing Ochrobactrum sp. SSR is multifaceted PSB.…”

“…The applied bacterial strains solubilized RP and phytate. Previously these bacteria were reported to solubilize P from tricalcium phosphate (Yahya et al, 2021 ). Our data supports the view that the utilization of multiple P sources by bacteria assures that they release P in different substrates and environments, and exhibit a strong potential for applications (Wan et al, 2020 ).…”

“…Multiple traits of the PSB are directly involved in the bioavailability and P uptake by the plants. The PSB-enhanced nutrient-sensing capacity of the plants, which has already been made available by the secretion of bacterial organic acids (Chungopast et al, 2021 ; Yahya et al, 2021 ). The PSB modulates the morphology of root architecture and alleviates the P-stress by making P available in the soil and stimulating the plants to uptake P. This tripartite system could lead to improved crop vigor and yield.…”

“…The agronomic performance of the potential inoculant tested under field trial, appraise the superiority of the inoculant. The various studies demonstrate that P-solubilizing microbes showed best effect with reduced application of DAP fertilizers (Suleman et al, 2018 ; Rosa et al, 2020 ; Rasul et al, 2021 ; Yahya et al, 2021 ).…”

“…ZW9, ZW32 (GenBank accession numbers MK422617 and MK817561 ) and Ochrobactrum sp. SSR (GenBank accession number MK422612 ) used in this study were isolated from the wheat rhizosphere and characterized in our previous study (Yahya et al, 2021 ). These PSB are non-pathogenic, compatible with each other and were also submitted to DSMZ ( https://www.dsmz.de/ ) culture collection under the accession numbers DSM 109610 and DSM 109592 , DSM 109593 for Ochrobactrum sp.…”