Abstract
Soil salinity is one of the most important abiotic factors limiting plant productivity. The aim of this study was to determine the effect of selected halotolerant plant growth-promoting endophytes (PGPEs, Pseudomonas stutzeri ISE12 and Kushneria marisflavi CSE9) on the growth parameters of barley (Hordeum vulgare), lettuce (Lactuca sativa), and sunflower (Helianthus annuus) cultivated under salt stress conditions. A negative effect of two higher tested salinities (150 and 300 mM NaCl) was observed on the growth parameters of all investigated plants, including germination percentage and index (decreasing compared to the non-saline control variant in the ranges 5.3–91.7 and 13.6–90.9%, respectively), number of leaves (2.2–39.2%), fresh weight (24.2–81.6%); however, differences in salt stress tolerance among the investigated crops were observed (H. annuus > H. vulgare > L. sativa). Our data showed that the most crucial traits affected by endophyte inoculation under salt stress were chlorophyll concentration, leaf development, water storage, root development, and biomass accumulation. Thus, the influence of endophytes was species specific. K. marisflavi CSE9 promoted the growth of all tested plant species and could be considered a universal PGPEs for many plant genotypes cultivated under saline conditions (e.g., increasing of fresh weight compared to the non-inoculated control variant of barley, lettuce, and sunflower in the ranges 11.4–246.8, 118.9–201.2, and 16.4–77.7%, respectively). P. stutzeri ISE12 stimulated growth and mitigated salinity stress only in the case of barley. Bioaugmentation of crops with halotolerant bacterial strains can alleviate salt stress and promote plant growth; however, the selection of compatible strains and the verification of universal plant stress indicators are the key factors.
Highlights
The increasing world population and associated rising demand for agricultural products continually contribute to soil degradation (Adejumobi et al, 2016; Temme et al, 2019) and soil salinization is one of the most critical consequences
The main objective of the current work was to evaluate: (i) the tolerance of three crops (H. vulgare, L. sativa, and H. annuus) to increasing salinity, (ii) the effect of inoculation with P. stutzeri ISE12 or K. marisflavi CSE9 on the plant growth parameters of H. vulgare, L. sativa, and H. annuus growing under different salt stress conditions (0, 50, 150, 300 mM NaCl) and (iii) the selection criteria of universal plant growth parameters susceptible to changes caused by salinity and inoculation
H. vulgare plants grown under salt condition were smaller than those grown in the control variant (0 mM NaCl): was calculated as fresh (Wf), Wd, number of leaves (NoL) (16.7–39.2%), and RL (25.7% to above 42.4%)
Summary
The increasing world population and associated rising demand for agricultural products continually contribute to soil degradation (Adejumobi et al, 2016; Temme et al, 2019) and soil salinization is one of the most critical consequences. Saline areas occur in at least 100 countries and cover 932.2 Mha worldwide (Cuevas et al, 2019). Due to the level of salinity, soils have been divided into non-saline (ECe 0–2 dS/m), slightly saline (ECe 2–4 dS/m), moderately saline (ECe 4–8 dS/m), strongly saline (ECe 8–16 dS/m), and extremely saline (ECe > 16 dS/m) (Corwin and Scudiero, 2019). Increasing soil salinization decreases seed germination, plant growth and development, water and nutrient uptake, and physiological (e.g., photosynthesis) and biochemical processes of plants (Isayenkov and Maathuis, 2019; Kumar et al, 2020). The tolerance level of plants to salinity may depend on the species, cultivar and growth phase (Munns and Tester, 2008; Rajabi Dehnavi et al, 2020). A small group of plants, known as halophytes, have the ability to grow in salt conditions exceeding 200 mM NaCl, while the vast majority of plants are in the group of glycophytes (including most crops) that cannot accumulate salts in plant tissues but are able to survive in saline environments (Carillo et al, 2011; Batool et al, 2014; Guo et al, 2021)
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