Abstract
Mediterranean areas with intensive agriculture are characterized by high salinity of groundwater. The use of this water in hydroponic cultivations can lead to nutrient solutions with an electrical conductivity that overcomes the tolerance threshold of many vegetable species. Plant growth-promoting rhizobacteria (PGPR) were shown to minimize salt stress on several vegetable crops but the studies on the application of PGPR on leafy vegetables grown in hydroponics are rather limited and have not been used under salt stress conditions. This study aimed to evaluate the use of plant growth-promoting bacteria to increase the salt tolerance of leaf lettuce grown in autumn and spring in a floating system, by adding a bacterial biostimulant (1.5 g L−1 of TNC BactorrS13 a commercial biostimulant containing 1.3 × 108 CFU g−1 of Bacillus spp.) to mineral nutrient solutions (MNS) with two salinity levels (0 and 20 mM NaCl). Leaf lettuce plants showed a significant reduction of growth and yield under salt stress, determined by the reduction of biomass, leaf number, and leaf area. Plants showed to be more tolerant to salinity in autumn than in spring. The inhibition of lettuce plant growth due to salt stress was significantly alleviated by the addition of the bacterial biostimulant to the MNS, which had a positive effect on plant growth and fresh and dry biomass accumulation of the unstressed lettuce in both cultivation seasons, and maintained this positive effect in brackish MNS, with similar or even significantly higher values of morphologic, physiologic, and yield parameters than those recorded in control unstressed plants.
Highlights
The need to attend the increasing food demand while protecting the environment and reducing the use of natural resources led to the search for more sustainable agriculture [1]
The commercial bacterial biostimulant (1.5 g L−1 of TNC BactorrS13 ) contains plant growth-promoting bacteria (1.3 × 108 CFU g−1 of Bacillus amyloliquefaciens, B. brevis, B. circulans, B. coagulans, B. firmus, B. halodenitrificans, B. laterosporus, B. licheniformis, B. megaterium, B. mycoides, B. pasteurii, B. subtilis, Paenibacillus polymyxa), as well as megaterium, B. mycoides, B. pasteurii, B. subtilis, Paenibacillus polymyxa), as well as soluble humates, soluble humates, natural plant hormones, amino acids, vitamins, and trace elements derived from natural plant hormones, amino acids, vitamins, and trace elements derived from Ascophylum
The hydroponic system consisted of polystyrene panels floating on the mineral nutrient solution (MNS)
Summary
The need to attend the increasing food demand while protecting the environment and reducing the use of natural resources led to the search for more sustainable agriculture [1]. This major challenge of agricultural research is hindered by the rapid growth of the human population and the decreasing availability of natural resources and land for cultivation [2]. Salt stress affects vegetable growth due to the osmotic or water-deficit effect, toxic accumulation of salts in shoots, nutritional imbalances, or a combination of these factors [6,7]
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