Use of Gibberellic Acid to Increase the Salt Tolerance of Leaf Lettuce and Rocket Grown in a Floating System

Abstract

Hydroponics need water of good quality to prepare a balanced nutrient solution that could allow plants to reach their maximum yield potential. The rising difficulties in finding water with good quality have led to the compelling necessity of identifying sustainable ways to use saline water, limiting its negative effect on crop yield and quality. The exogenous supplementation of plant growth regulators, such as gibberellic acid (GA3), can be effective in increasing plant growth and vigor, thus helping plants to better cope with salt stress. The aim of this study was to evaluate the feasibility to increase the salt tolerance of leaf lettuce and rocket grown in a floating system by adding GA3 (10−6 M) to mineral nutrient solutions (MNS) with increasing salinity (0, 10, and 20 mM NaCl). Leaf lettuce and rocket plants suffered a significant reduction of growth and yield, determined by the reduction of biomass, leaf number, and leaf area, even with moderate salt stress (10 mM NaCl). The supplementation of exogenous GA3 through the MNS allowed plants to substantially counterbalance salt stress by enhancing various morphological and physiological traits, such as biomass accumulation, leaf expansion, stomatal conductance and water and nitrogen use efficiency. The effects of salt stress and GA3 treatment varied according to the species, thus indicating that this interaction may improve salt tolerance by activating different adaptation systems.

Fertigation Management and Growth-Promoting Treatments Affect Tomato Transplant Production and Plant Growth after Transplant

“…The changes in leaf color were determined by changes in the pigment content (chlorophylls and carotenoids) that are highly related to the color components measured with a colorimeter [81][82][83]. They can be symptoms of nutrient deficiencies or excesses and are an indicator of the plant's nutritional or stress status [11,84] as found in our work, by increasing nutrient supply to the control and GA 3 -treated seedlings.…”

“…The effect of GA 3 treatments on tomato plants during field growth has been investigated several times, recording a positive effect on the growth, biomass accumulation, yield, and yield attributes [37,[86][87][88]. The positive effects of exogenous GA 3 application on plant growth and yield under different growth conditions are well known and involve, among others, the modification of source/sink relationships [9][10][11]89] as reported above for tomato seedlings under different fertigation rates. These growth-promoting effects were not evident after the transplant of tomato seedlings, and plant modification due to GA 3 treatments was limited to minor parameters.…”

Effect of Bacterial Inoculum and Fertigation Management on Nursery and Field Production of Lettuce Plants

“…The influence of PGPR could be mediated by their phytohormone production, especially regarding gibberellins. Gibberellins affect nitrogen metabolism and nitrogen translocation in plants by improving utilization of N through increased nitrate reductase activity [65,66], resulting in increased yield and lower nitrate accumulation [67][68][69][70]. Another response of plants to inoculation with PGPR is the increased accumulation of chlorophyll and carotenoids [48], but in our study, the only significant effect of the bacterial biostimulant was recorded in the a* values of lettuce leaves showing that there was no significant modification of leaf pigments as a function of bacterial inoculum, whereas leaves were affected by the highest fertigation rate during transplant production as they had a more vivid but less greenish color.…”

Alleviation of Salt Stress by Plant Growth-Promoting Bacteria in Hydroponic Leaf Lettuce

“…In these cultivation systems, plants are fed through a mineral nutrient solution and held by mineral or organic materials that anchor the roots, or by panels that host them and float on the nutrient solution (floating system). The water used to prepare nutrient solutions must have good quality characteristics, especially with regards to low salt concentration, as it can influence the electrical conductivity (EC) of the nutrient solution, once water-soluble mineral fertilizers are added to the water [16]. Mediterranean areas with intensive agriculture are characterized by high salinity of groundwater, as the considerable use of irrigation water increases seawater infiltration [17].…”

“…These mechanisms are triggered by hormonal signaling, as revealed by the modifications of the endogenous levels of phytohormones found in plants, which grow under salt stress [19,20]. Thus, some strategies employed to increase salt tolerance of vegetable crops and mitigate the negative effects of salinity focus on the exogenous application of plant growth regulators (gibberellins, auxins, and cytokinins) [16,20], or the inoculation of the rhizosphere with root colonizing bacteria, which produce phytohormones [21,22]. Plant growth-promoting rhizobacteria (PGPR) were shown to minimize salt stress on several vegetable crops [23,24].…”