Abstract
Salicornia bigelovii is a promising halophytic cash crop that grows in seawater of the intertidal zone of the west-north coast of the UAE. This study assess plant growth promoting (PGP) capabilities of halotolerant actinobacteria isolated from rhizosphere of S. bigelovii to be used as biological inoculants on seawater-irrigated S. bigelovii plants. Under laboratory conditions, a total of 39 actinobacterial strains were isolated, of which 22 were tolerant to high salinity (up to 8% w/v NaCl). These strains were further screened for their abilities to colonize S. bigelovii roots in vitro; the most promising ones that produced indole-3-acetic acid, polyamines (PA) or 1-aminocyclopropane-1-carboxylic acid (ACC) deaminase (ACCD) were selected for rhizosphere-competency under naturally competitive environment. Three outstanding rhizosphere-competent isolates, Streptomyces chartreusis (Sc), S. tritolerans (St), and S. rochei (Sr) producing auxins, PA and ACCD, respectively, were investigated individually and as consortium (Sc/St/Sr) to determine their effects on the performance of S. bigelovii in the greenhouse. Individual applications of strains on seawater-irrigated plants significantly enhanced shoot and root dry biomass by 32.3–56.5% and 42.3–71.9%, respectively, in comparison to non-inoculated plants (control). In addition, plants individually treated with Sc, St and Sr resulted in 46.1, 60.0, and 69.1% increase in seed yield, respectively, when compared to control plants. Thus, the synergetic combination of strains had greater effects on S. bigelovii biomass (62.2 and 77.9% increase in shoot and root dry biomass, respectively) and seed yield (79.7% increase), compared to the control treatment. Our results also showed significant (P < 0.05) increases in the levels of photosynthetic pigments, endogenous auxins and PA, but a reduction in the levels of ACC in tissues of plants inoculated with Sc/St/Sr. We conclude that the consortium of isolates was the most effective treatment on S. bigelovii growth; thus confirmed by principal component and correlation analyses. To this best of our knowledge, this is the first report about halotolerant rhizosphere-competent PGP actinobacteria thriving in saline soils that can potentially contribute to promoting growth and increasing yield of S. bigelovii. These halotolerant actinobacterial strains could potentially be exploited as biofertilizers to sustain crop production in arid coastal areas.
Highlights
Saline water dominates the earth, but the supply of fresh water has always been limited especially in the arid regions of the world
In the United Arab Emirates (UAE), the production of aviation biofuel can be derived from halophytic plants such as Salicornia spp. that can successfully grow in salt marshes
It is known that Plant growth-promoting rhizobacteria (PGPR) can improve plant growth by enhancing nutrient recycling and producing plant growth regulators (PGRs); minimizing the application of chemical fertilization (Hassan et al, 2019)
Summary
Saline water dominates the earth, but the supply of fresh water has always been limited especially in the arid regions of the world. “clean” fresh water scarcity is a major problem in many arid and semi-arid regions in the world, including the United Arab Emirates (UAE) (Odhiambo, 2017). This can be considered a major constraint for sustainable development in agriculture and food production. There is an urgent need to meet the ever-increasing demand for food and agriculture products in such countries with crops that could be irrigated with saline or seawater. S. bigelovii is a main component of biofuel feedstock cultivated with aquaculture and mangrove silviculture in the Seawater Energy and Agriculture System (SEAS) to promote integrated food-energy in desert farms (Ray and Anumakonda, 2011; Ríos, 2014; Sharma et al, 2016)
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