Plant biostimulants are of interest as they can stimulate plant growth and increase resource utilization. There is still no information on the use of plant growth-promoters under variable nutritional conditions in the nursery and the effects on tomato seedling growth and plant performance after transplant. This study aimed to evaluate the suitability of gibberellic acid (GA₃) or bacterial biostimulant treatments to enhance the growth and quality of greenhouse-grown tomato (Solanum lycopersicum ‘Marmande’) seedlings, fertigated with increasing nutrient rates and to assess the efficacy of these treatments on the early growth of tomato plants. During autumn 2019, tomato seedlings were inoculated with 1.5 g L⁻¹ of TNC Bactorr^S13 (a commercial biostimulant containing 1.3 × 10⁸ CFU g⁻¹ of Bacillus spp.) or sprayed with 10⁻⁵ M GA₃ and fertigated with a nutrient solution containing 0, 1, 2 and 4 g L⁻¹ of NPK fertilizer (20-20-20) when they reached the 11th BBCH growth stage for tomato. Subsequently, the seedlings were evaluated in greenhouse cultivation for 60 days until at least the 61st BBCH growth stage (January 2020). The growth of the tomato seedlings increased curvilinearly in relation to the fertigation rates. The GA₃-treated seedlings showed similar or even higher growth parameters than the control seedlings fed with 4 g L⁻¹ of fertilizer but with half of the nutrients. The inoculation of the substrate with Bacillus spp. had negative effects in the absence of fertigation but determined a greater growth at the highest fertigation rate. The bacterial inoculum of seedlings had longer-term effects than the GA₃ treatment during the plant growth, but these effects were noticeable mainly when the bacterial biostimulant was associated with the highest fertigation rate.

The shortage of good quantity and quality of water for irrigated agriculture is a major problem in arid and semiarid regions. To deal with this problem, deficit irrigation (DI) or arbuscular mycorrhizal fungi (AMF) inoculation have been proposed and adopted for many crops as a tool to save water, or to improve crop tolerance to drought stress. An experiment was conducted for two consecutive years to evaluate the effect of mycorrhizal inoculation on the physiological, morphological, yield, and quality characteristics of melon plants grown under deficit irrigation. Melon crop (Cucumis melo L. cv. Helios) was grown under field conditions adopting a split-plot design with four replications, where DI was the main factor and AMF inoculation was the secondary factor. DI treatments consisted of applying 60%, 80%, or 100% of crop evapotranspiration (ETc) on melon plants inoculated or not with a commercial biostimulant containing 50% of Rhizophagus irregularis, and 50% of Funneliformis mosseae. Moderate and severe deficit irrigation significantly reduced the relative water content, stomatal conductance, yield, nitrogen applied efficiency (NAE), and fruit firmness of the uninoculated plants, but significantly increased irrigation water use efficiency (IWUE) and the ascorbic acid content of the fruit. AMF had a positive effect on plant tolerance to moderate water stress, and on some fruit quality parameters (fruit length, firmness, and sugar content). The combined use of moderate deficit irrigation (80%) and soil inoculation with AMF on melon plants allows water savings without affecting fruit yield, and increases IWUE, NAE, and some fruit quality characteristics (firmness, SSC, and SSC/TA). Furthermore, the use of AMF plants could be worth it to reduce the yield loss and increase fruit quality, even with severe deficit irrigation (60%).

Ecklonia maxima and the commercial biostimulants produced from it contain various plant growth regulators that are responsible for the growth stimulation recorded in many crops. Auxins are one of the major plant growth regulators contained in E. maxima extracts. The aim of this research was to evaluate the growth-promoting effect of a seaweed extract from E. maxima on lettuce and tomato transplant production under nursery conditions, and to compare the effect of this extract with an equal concentration of synthetic auxin. Two doses of natural or synthetic exogenous auxins (50 or 100 μg L⁻¹) were supplied to the substrate through the irrigation water with an ebb and flow system, 4, 11, and 18 days after sowing. A commercial biostimulant based on E. maxima extract was used as a source of natural auxin, while 1-naphthaleneacetic acid (NAA) was used as a synthetic auxin. Seedlings supplied only with water were used as a control. Tomato seedlings treated with 100 μg L⁻¹ of natural auxins from E. maxima extract produced the tallest plants (+22%), with a higher leaf number (+12%), a wider leaf area (+44%), and a stronger stem (+12%), whereas lettuce seedling growth was promoted by all the treatments, but with a greater effect with increasing auxin supplementation and when using E. maxima extract, compared to NAA. The results showed that the supplementation of exogenous synthetic auxin (NAA), or an E. maxima extract containing natural auxins, can have a growth-promoting effect on lettuce and tomato seedlings. This effect was more evident on lettuce than tomato. The biostimulant produced from E. maxima extracts improved seedling quality and promoted shoot and root growth more than the NAA used as a synthetic source of auxins.

A correct cultivation technique supported by scientific evidence that leads to high-quality standards can promote sustainable floriculture. It is urgent to find alternative solutions to the widely used chemical fertilizers and evaluate the effectiveness of other fertilizers. The liquid organic ones, already in use in organic vegetable farming, could be a good substitute if supplied together with growth-promoting products such as microbial biostimulants. In the hope of replacing the traditional chemicals with a more sustainable organic-based fertilization, the present investigation aimed to evaluate the effects of a microbial biostimulant and various combinations of organic and mineral fertilization on morphological characteristics and physiological parameters of Tagetes patula L. and Ageratum houstonianum Mill. The plants were grown in pots with a substrate inoculated or not with the microbial biostimulant and were fertigated with nutrient solutions at different concentrations of elements from mineral and/or organic sources. Six fertilization formulas were adopted: control (only water without fertilizer), 100% mineral fertilization, 50% mineral fertilization, 100% organic fertilization, 50% organic fertilization, and 50% mineral + 50% organic fertilization. For the organic fertilization, a commercial liquid fertilizer admitted in organic farming with 3-2-5.5 NPK with 3% organic nitrogen was used. Mineral fertilization was formulated to match the organic solution as closely as possible. We observed an improvement in ornamental value (stem diameter and shoot number) with the biostimulant inoculum. Generally, the 50% mineral and 50% organic fertilization did not negatively influence the morphological characteristics. The reduction by 50% in the mineral nutrients and the integration of this reduction with an organic fertilizer was feasible to produce potted plants of these species during spring in the Mediterranean area.

In the context of increasing demand for sustainable floriculture, this study evaluated the effects of salicylic acid (SA) on phenotypic traits of poinsettia (Euphorbia pulcherrima Willd.). A factorial experiment was conducted in a commercial glasshouse using rooted poinsettia cuttings treated with three SA concentrations (10⁻³, 10⁻⁴, 10⁻⁵ M) applied via foliar or root application. Morphological parameters, colorimetric traits (CIELAB), canopy development, and biomass accumulation were assessed throughout the cultivation cycle. SA had no significant influence on the plant height, leaf number, or biomass of stems, leaves, and roots. However, notable phenotypic changes were observed. Foliar applications, particularly at 10⁻⁵ M, induced visible changes in leaf and bract color, including reduced brightness, saturation, and red pigmentation, especially in newly developed tissues. Conversely, root applications had milder effects and were generally associated with a more stable bract color. The 10⁻⁴ M root treatment promoted greater bract surface and color saturation. Canopy expansion and dry matter accumulation were also influenced by SA in a dose- and method-dependent manner, with high-dose foliar treatments (10⁻³ M) exerting suppressive effects. These findings suggest that the application mode and concentration of SA are critical in modulating ornamental quality traits, with low-to-moderate doses—particularly via root application—offering promising strategies to enhance plant performance in sustainable poinsettia cultivation.

Tetragonia tetragonioides, or New Zealand spinach, is a widespread halophyte native to eastern Asia, Australia, and New Zealand, and naturalized in some Mediterranean regions. This underutilized vegetable is consumed for its leaves, raw or cooked. For the first time, we investigated the feasibility of using whole baby plants (including stems and leaves) as raw material for ready-to-eat (RTE) vegetable production. Our study assessed Tetragonia’s suitability for hydroponic cultivation over two cycles (autumn–winter and spring). We investigated the impact of increasing nutrient rates (only water, half-strength, and full-strength nutrient solutions) and plant densities (365, 497, and 615 plants m⁻² in the first trial and 615 and 947 plants m⁻² in the second) on baby plant production. We also analyzed the plants’ morphological and biochemical characteristics, and their viability for cold storage (21 days at 4 °C) as a minimally processed product. Tetragonia adapted well to hydroponic cultivation across both growing periods. Nevertheless, climatic conditions, plant density, and nutrient supply significantly influenced plant growth, yield, nutritional quality, and post-harvest storage. The highest plant density combined with the full-strength nutrient solution resulted in the highest yield, especially during spring (1.8 kg m⁻²), and favorable nutritional characteristics (β-carotene, Vitamin C, Fe, Cu, Mn, and Zn). Furthermore, Tetragonia baby plants proved suitable for minimal processing, maintaining good quality retention for a minimum of 14 days, thus resulting in a viable option for the RTE vegetable market.