Table3_Mitigation of salt stress in Sorghum bicolor L. by the halotolerant endophyte Pseudomonas stutzeri ISE12.docx

Increasing soil salinity, exacerbated by climate change, threatens seed germination and crop growth, causing significant agricultural losses. Using bioinoculants based on halotolerant plant growth-promoting endophytes (PGPEs) in modern agriculture is the most promising and sustainable method for supporting plant growth under salt-stress conditions. Our study evaluated the efficacy of Pseudomonas stutzeri ISE12, an endophyte derived from the extreme halophyte Salicornia europaea, in enhancing the salinity tolerance of sorghum (Sorghum bicolor L.). We hypothesized that P. stutzeri ISE12 would improve sorghum salt tolerance to salinity, with the extent of the increase in tolerance depending on the genotype’s sensitivity to salt stress. Experiments were conducted for two sorghum genotypes differing in salinity tolerance (Pegah - salt tolerant, and Payam - salt sensitive), which were inoculated with a selected bacterium at different salinity concentrations (0, 100, 150, and 200 mM NaCl). For germination, we measured germination percentage and index, mean germination time, vigor, shoot and root length of seedlings, and fresh and dry weight. In pot experiments, we assessed the number of leaves, leaf area, specific leaf area, leaf weight ratio, relative root weight, plantlet shoot and root length, fresh and dry weight, proline and hydrogen peroxide concentrations, and peroxidase enzyme activity. Our study demonstrated that inoculation significantly enhanced germination and growth for both sorghum genotypes. The salinity-sensitive genotype (Payam) responded better to bacterial inoculation during germination and early seedling growth stages, showing approximately 1.4 to 1.8 times greater improvement than the salinity-tolerant genotype (Pegah). Payam also displayed better performance at the plantlet growth stage, between 1.1 and 2.6 times higher than Pegah. Furthermore, inoculation significantly reduced hydrogen peroxide, peroxidase activity, and proline levels in both sorghum genotypes. These reductions were notably more pronounced in Payam, with up to 1.5, 1.3, and 1.5 times greater reductions than in Pegah. These results highlight the efficacy of P. stutzeri ISE12 in alleviating oxidative stress and reducing energy expenditure on defense mechanisms in sorghum, particularly benefiting salt-sensitive genotypes. Our findings highlight the potential of the bacterial endophyte P. stutzeri ISE12 as a valuable bioinoculant to promote sorghum growth under saline conditions.

气候变化加剧的土壤盐渍化正威胁种子萌发与作物生长，造成严重的农业损失。在现代农业中，基于耐盐促植物生长内生菌（halotolerant plant growth-promoting endophytes, PGPEs）的生物菌剂，是盐胁迫环境下支持植物生长最具前景且可持续的技术手段。本研究评估了从极端盐生植物盐角草（Salicornia europaea）中分离得到的内生菌施氏假单胞菌ISE12（Pseudomonas stutzeri ISE12）提升高粱（Sorghum bicolor L.）耐盐性的功效。我们提出假说：施氏假单胞菌ISE12可改善高粱的耐盐能力，且耐盐性提升的幅度取决于不同基因型对盐胁迫的敏感程度。实验选取了两种耐盐性存在差异的高粱基因型——耐盐品种Pegah与盐敏感品种Payam，分别在0、100、150、200 mM NaCl不同盐浓度梯度下接种目标菌株。萌发实验中，我们测定了萌发率、萌发指数、平均萌发时间、活力指数、幼苗地上部与根系长度，以及鲜重与干重。盆栽实验中，我们评估了叶片数、叶面积、比叶面积、叶重比、相对根重、幼苗地上部与根系长度、鲜重与干重，以及脯氨酸、过氧化氢浓度与过氧化物酶活性。本研究结果表明，接种该菌株可显著提升两种高粱基因型的萌发与生长表现。盐敏感基因型Payam在萌发期与幼苗早期生长阶段对细菌接种的响应更佳，其性能提升幅度约为耐盐基因型Pegah的1.4至1.8倍。在幼苗生长阶段，Payam同样表现更优，性能提升幅度为Pegah的1.1至2.6倍。此外，接种菌株可显著降低两种高粱基因型体内的过氧化氢含量、过氧化物酶活性与脯氨酸水平，且该降低效应在Payam中更为显著，其降幅分别较Pegah最高高出1.5、1.3与1.5倍。上述结果凸显了施氏假单胞菌ISE12在缓解高粱氧化应激、减少防御机制能量消耗方面的功效，尤其对盐敏感基因型更为有益。本研究结果证实，内生细菌施氏假单胞菌ISE12作为一种极具价值的生物菌剂，在盐渍化环境下促进高粱生长具备广阔的应用潜力。