Rhizobacteria From Root Nodules of an Indigenous Legume Enhance Salinity Stress Tolerance in Soybean

Abstract

Soybean is the most widely grown legume worldwide, but it is a glycophyte and salinity stress can decrease its yield potential up to 50%. Plant growth promoting rhizobacteria (PGPR) are known to enhance growth and induce tolerance to abiotic stresses including salinity. The aim of this study was to isolate such PGPR from the root nodules of Amphicarpaea bracteata, a North American relative of soybean. Isolated strains were identified, and 15 strains were screened for potential utilization as PGPR of soybean through a series of greenhouse trials. Four isolates that greatly improved shoot and root growth were further selected and screened under a range of salt concentrations. Two of the most promising strains, Rhizobium sp. SL42 and Hydrogenophaga sp. SL48 were ascertained to exert the greatest beneficial effects on soybean growth and salinity tolerance. They were co-inoculated with Bradyrhizobium japonicum 532C (Bj) and the plants were grown up to the harvest stage. The treatment of Bj+SL42 resulted in higher shoot biomass than the control, 18% at the vegetative stage, 16% at flowering, 7.5% at pod-filling, and 4.6% at harvest and seed weight was increased by 4.3% under salt stress (ECe = 7.4 ds/m). Grain yield was raised under optimal conditions by 7.4 and 8.1% with treatments Bj+SL48 and Bj+SL42+SL48, respectively. Nitrogen assimilation and shoot K+/Na+ ratio were also higher in the co-inoculation treatments. This study suggested that inoculation with bacteria from an indigenous legume can induce stress tolerance, improve growth and yield to support sustainability, and encourage ecological adaptability of soybean.

Overview of the Role of Rhizobacteria in Plant Salt Stress Tolerance

“…SL42, and Hydrogenophaga sp. SL48 onto soybean plants under saline conditions improved shoot and root growth, nitrogen assimilation, and the K + /Na + ratio, which could be a consequence of nodular-symbiotic and source-sink activities [44]. Capsicum annuum L. plants co-inoculated with Azospirillum brasilense M3 and Pantoea dispersa C3 under salinity (40-120 mM NaCl) showed increases in analyzed production parameters, as related to higher stomatal conductance and photosynthesis, without changes in chlorophyll content or photosystem efficiency [45].…”

Growth and Yield of Soybeans in Various Growing Media Composition and Inoculation of Rhizobacteria on Marginal Soils

“…This shows that the inoculum originating from the soil previously planted with soybeans still contains a lot of effective Rhizobium bacteria. Indigenous Rhizobium sp inoculated can form nodules, but not all inoculants are effective for soybean plants (Abd-Alla et al 2014;Banerjee et al 2016;Goyal and Goel 2018;Franzini et al 2019;Ilangumaran et al 2021). Rhizobium bacteria are soil microbes capable of binding free nitrogen in the air into ammonia (NH3), which will be converted into amino acids become nitrogen compounds needed by plants to grow and develop (Tilak et al 2006;Ahmed et al 2016;Ren et al 2019).…”

Cell-Free Supernatant Obtained From a Salt Tolerant Bacillus amyloliquefaciens Strain Enhances Germination and Radicle Length Under NaCl Stressed and Optimal Conditions

“…NaCl (75 mM NaCl and 50 mM NaCl) lowered mean percentage and mean radicle length of both soybean and corn, in some cases, significantly, in others not. Salinity stress is a major global abiotic stress that affects crops, at all stages of development, including seed germination, radicle length and general plant growth (Subramanian et al, 2016;Ilangumaran et al, 2021). As little as 0.1 M NaCl causes visible reductions in plant height in some corn cultivars, compared to corn grown under optimal conditions (Farooq et al, 2015).…”

“…Na + , Cl − , Mg 2+ , and SO 2− 4 ions are the most dominant in saline soils, due their high solubility, and hence, ease of deposition by water, of minerals such as NaCl, MgSO 4 , CaSO 4 , MgCl 2 , KCl, Na 2 CO 3 , Na 2 SO 4 and [Na 2 Mg(SO 4 ) 2 ] (Tanji, 2002), NaCl the dominant in most saline environments (Forni et al, 2017). Salinity may cause osmotic, ionic and oxidative stresses in the seed, which may delay or cause complete failure of a seed to germinate (Rouhi et al, 2011;Ansari and Sharif Zadeh, 2012;Ilangumaran et al, 2021). Osmotic stress may result in reduced activity or denaturation of plant cytosolic and organelle proteins (Forni et al, 2017), decrease of cytosolic and vacuolar volumes which may negatively impact plant growth, due to reduced photosynthesis and increased production of reactive oxygen species (ROS), which may be detrimental to plant cell components and physiology (Forni et al, 2017).…”

“…Use of PGPM technology, is a potentially sustainable and ecofriendly mechanism of mitigating salinity stress effects on crops (Ilangumaran et al, 2021;Naamala and Smith, 2021a,b). Use of pure microbial derived active compounds is especially a section of PGPM technology, that has currently gained popularity due to ease of patent and certification process compared to live cells (García-García et al, 2020;Naamala and Smith, 2020).…”