Upon microbial infection or treatment with biostimulants, plants often become primed for an enhanced response to biotic (e.g., pathogens) or abiotic stress (e.g., drought, cold, and heat). Defense priming involves an increase in microbial pattern receptors (e.g., flagellin-sensing 2), accumulation of dormant stress signaling enzymes (e.g., mitogen-activated protein kinases 3 and 6) in response to the priming event, and modifications to chromatin. Together, these events establish a memory of the initial stimulus and enable a heightened recall response to stress. I will summarize these fascinating discoveries and explore their potential for sustainable agriculture by introducing smart tools and approaches for identifying and utilizing priming-inducing compounds and microbes.

Biostimulants offer a new approach to alleviating stress-induced plant growth limitations (Ali et al., 2021). Laminaria sp. extracts and in particular the laminarans are known for their protective effect against biotic stress (Agarwal et al., 2021), while their effects against abiotic stress, and especially drought, remain largely unknown. We have previously demonstrated the ability of different Laminaria digitata extracts to improve cell membrane stability in the leaf meristem of perennial ryegrass (Lolium perenne) subjected to drought (Grandin-Courbet et al., 2024). In the present study, we analysed separately the effects of the main ingredients of Laminaria sp. namely alginates, fucoidans, laminarans and mannitol. The ingredients were sprayed onto the leaves at different concentrations at the start of the priming period, seven days before irrigation was stopped. Indicators of leaf meristem protection, namely cell membrane stability, osmotic adjustment and carbohydrate content, were monitored at the end of the drought period. Leaf growth was monitored at the end of the recovery period. Treatments with each of the ingredients improved membrane stability in leaf meristems during drought, but with different optimal concentrations. During the recovery period, the greatest improvement in regrowth was obtained for plants supplied with laminarans, suggesting that for this ingredient, additional mechanisms are involved during the recovery period. The effect of the ingredients on improving nitrogen uptake during the recovery period is currently being assessed using 15N isotope labelling. In addition, transcriptomic analyses are underway to understand the underlying mechanisms by which each ingredient triggers drought resistance in perennial ryegrass.

Biostimulants are one of the most promising and eco-friendly advances, able to boost qualitative and quantitative plant traits[1]. There are evidences that biostimulants supply promotes seedling emergence and rooting, improves yields, plant growth, fruit set, flowering, and overall production quality[2], also under biotic and/or abiotic distresses[3]. Biofortification is a technique used to reduce the incidence of mineral malnutrition in the world population by increasing the concentration of micronutrients in plants[4]. However, agronomic biofortification programmes can cause phytotoxicity issues, compromising the success of biofortification itself. In this scenario, the potential use of microbial or non-microbial biostimulants for the alleviation of micronutrients stress was explored. There are evidences that the application of a plant protein hydrolysates on lettuce had a buffer effect against high Mo dosages (6.0 µmol L-1), promoting plant performance and quality[5]. Some authors also found that the supply of an Ecklonia maxima seaweed extract on Mo-biofortified spinach was useful to modulate plant nutritional status, resulting in an enhanced plant Mo tolerance and accumulation[6]. Furthermore, it was reported that seaweed extracts can be also employed for the mitigation of high iodine dosage stress (up to 300 mg L-1) in strawberry plants[7]. Microbial biostimulants, such as arbuscular mycorrhizal fungi, could be useful for increasing sweet pepper tolerance to molybdenum at high dosages (6 µmol L-1)[8]. In conclusion, these studies could provide important information in the context of agronomic biofortification programs, providing a baseline for future studies on the topic that are necessary.

Water scarcity and heat waves, caused by climate change, lead to yield losses, and threaten farmers livelihoods, human health, and nutrition. It has never been more urgent to act and create solutions toward plant resilience against abiotic stresses. The ag-tech company, Elicit Plant (elicit-plant.com), has developed a unique technology based on plant sterols for foliar application in broad-acre crops, as evidenced by 10 family patents across 4 continents. Driven by scientific hypotheses and discovery, proprietary formulation, and our platform technology, we have developed plant-specific products that result in 20% reduction in water intake and significant yield increases in broad-acre crops. We have demonstrated consistency of product performance globally. For example, in corn, 282 field trials conducted over 5 years in Europe, USA and Brazil showed up to 2 t/ha average yield increase at 90%-win rate. Our products also protect plants against heat stress. Here, we will present the mode of action and the plant molecular and phenotypic responses to both drought and heat stress. In summary, our platform delivers clear solutions for saving crop yields exposed to water deficit and heat. Since phytosterols have diverse functions and control some of the key plant processes, our technology may have the potential to create solutions for other plant stresses.

The benefits of seaweed based biostimulants to crop plants is well established. Similarly, the role of microbials in plant growth and yield enhancement is well documented. However, there is a limited knowledge in the understanding of how foliar application of seaweed based biostimulants can enrich plant beneficial microbes in plants rhizosphere. Herein, for the first time, we demonstrate how foliar application of a red seaweed based biostimulant induces root exudation in maize plants. Briefly, the foliar application of a Kappaphycus based product LBS06 positively influenced maize growth in terms of leaf area, plant height and shoot mass. Biochemical analysis confirmed enhanced accumulation of chlorophyll content (both a and b components), total carotenoids, soluble sugars and amino acids. Soil sample analysis revealed increase in total bacterial, fungal and actinomycetes counts in the rhizosphere soil. Further, soil metagenome studies using 16S rRNA primers indicates the clear differences in distribution of microbes across bulk soil, control treated plant soil and LBS06 treated maize rhizosphere soil.
Particularly, Paenibacillus, Flavobacterium, Nitrosomonas, Bacillus, Streptomyces, Bradirhizobium and many other plant growth promoting bacteria were observed to be enriched with LBS06 application. Additionally, the soil enzymes such as urease, acid phosphatase, FDAse, dehydrogenase, catalase along with biological index of soil fertility were increased in LBS06 treated maize plants rhizosphere soil. Overall, for the first time, we demonstrate how a red seaweed derived biostimulant can reprogram soil microbial content via the stimulation of root metabolite exudation.

Nitrogen plays a crucial role in agricultural crops, constituting a key nutrient for sustaining crop yields due to its involvement in biomass production. Implementing sustainable agronomic strategies, such as incorporating legumes into agroecological farming practices, could significantly reduce reliance on inorganic nitrogen fertilizers in agriculture. Cropped legumes uniquely meet their nitrogen needs through biological nitrogen fixation (BNF), facilitated by a symbiotic relationship with free-living, associative, endophytic and symbiotic rhizobacteria collectively termed rhizobia. BNF efficacy depends on factors including plant species, bacterial strains, soil quality and environmental conditions. Research on native rhizobia in fields without prior inoculation history is crucial for selecting locally adapted strains with superior performance, aiding in inoculant formulation. To this end, the genetic and symbiotic diversity of native rhizobia nodulating grain legumes (cowpea, common bean and faba bean) in Greek soil was investigated[1,2,3,4]. Most isolates were assigned to validly described species, while others constituted novel rhizobial lineages based on multilocus sequence analysis (MLSA). Greenhouse and field experiments using selected indigenous rhizobial strains as inoculants demonstrated increased nitrogen inputs, enhanced plant growth and yield when legumes were used as green manure or intercrops in organic farming[5,6,7,8,9]. Excessive synthetic nitrogen fertilizers were found to inhibit nodulation and BNF in legumes, while inoculation with native rhizobia reduced the need for inorganic nitrogen inputs in hydroponically grown cowpea and common bean without compromising plant performance[10,11]. In conclusion, research on native rhizobia strains, facilitates tailored solutions to nitrogen management, reducing reliance on synthetic fertilizers and enhancing crop productivity for long-term agricultural sustainability.

Georgia Ntatsi, Associate Professor, Agricultural University of Athens, Greece

Most agricultural soils have depleted pools of plant-available phosphorus (Pav) or are saturated with occluded forms of phosphorus (P) due to excessive use of inorganic P fertilizers to meet the demands of plant growth and development. The inefficacy of common P fertilizers, compounded with shifting geopolitical P markets and dwindling P reserves, necessitates strategies to increase Pav and phosphorus use efficiency (PUE) to improve resource management. Although promising, biostimulants containing single-strain phosphorus-solubilizing microbes (PSM) have shown variable to poor efficacy in-field, raising questions about the ecological relevance of a high solubilizing capacity. Microbial mechanisms for transforming occluded P extend far beyond the solubilization of inorganic P, and recent advancements in metagenomics and high-resolution technology have revealed the diverse complexity of phosphorus cycling microbes (PCM)
Hence, we aim to investigate PCM community structure, P-species distribution, and differential energy investment strategies of PCM at key spatial gradients of depth and root association in two commercial almond orchards in California. Our goal is to identify the parameters that inform the relevance and utility of specific P-cycling genes (PCGs), which have the potential to be used downstream in biostimulant research and development. Using next-generation metagenomic sequencing along with the most current and robust PCG databases available, and total reflection X-ray spectrometry (TXRF) for P-speciation, our continuing research aims to address the following hypotheses:
H1: PCG family abundance will proportionally co-occur with the abundance of P-species found along each spatial gradient, but PCG diversity will reflect the broader microbial community's differential energy strategies.
H2: Energy investment strategies will follow the spatial root-association gradient. Specifically, extracellular metabolic traits will increase with distance from the root, while intracellular metabolic traits will decrease.

Rhizosphere microorganisms, especially bacteria, play a key role in biostimulation of plant growth and development through a variety of biological mechanisms, which are intensively studied due to their growing potential for application in sustainable agriculture [1, 2, 3]. Significant biostimulant effects have been observed in studies of biopreparations containing selected strains of microorganisms carried out in the EXCALIBUR project "Exploiting the multifunctional potential of belowground biodiversity in horticultural farming", funded by the European Union's Horizon 2020 research and innovation program under grant agreement No 817946. The microorganisms, which act by solubilizing nutrients such as phosphorus, potassium or silicon and synthesizing plant hormones, promoted the development of the root system, resulting in a significant effect on overall plant growth and development. In addition, the microorganisms showed a protective effect against soil pathogens by inducing natural plant defense mechanisms [4].

The effect of bacteria on increasing soil biodiversity and biological activity was also particularly significant. In field trials with various crops, the use of these bacteria-based biopreparations resulted in increased yield quantity and quality, increased plant resistance to abiotic and biotic stresses, and improved soil physical properties. These results confirm the value of biopreparations in integrated and organic crop production, given the growing demand for environmentally friendly production methods.

As a result, microorganisms and their biostimulating properties represent a promising solution for the future of agriculture, with the potential to increase productivity while minimizing negative environmental impacts.

Microbiome biodiversity stands as the cornerstone for soil health, wielding profound implications for the sustainability of ecosystems and agricultural productivity.
The objective of this study was to assess the effect of a bacterial-based biostimulant on different soil microbiomes and crops performance under a wide range of environments. When assessed in tomato, the application resulted in an increase in yield of up to 6.2%. Exclusive bacteria and fungi genera were detected in the rhizosphere after the application, particularly on high fertility soils. Between 24 and 47% of these novel bacteria and fungi genera were reported to have functions that positively affects crops performance. In bean grown in a high fertility soil, the application of this biostimulant resulted in 19 and 24% higher shoot and root fresh biomass, respectively. For that type of soil, 4.5% and 74% of the bacterial and fungal genera were different than the control treatment, respectively. When tested in wheat, higher overall microbial biomass was detected in response to the treatment. The activity of different enzymes in the soil, particularly alkaline and acid phosphatases, was consistently and positively affected in part of these trials, explaining some of the mechanisms that are triggered. An in vitro assessment of the phosphorus solubilization capacity of this biostimulant, suggests the increase in phosphatases activity might be mediated by an enhancement of beneficial microbial communities.


This study demonstrates the ability of a bacterial-based biostimulant to boost the productivity of a wide range of agricultural systems by enhancing beneficial microbial communities within the soil.

We conducted a comparative study of high-throughput phenotyping technologies and ecophysiological analyses to assess the useful information they can provide under different stress conditions and their ability to detect responses to biostimulant applications. To achieve this goal, at PhenoPlant, the phenotyping platform of the University of Turin (https://en.disafa.unito.it/do/home.pl/View?doc=/research/infrastructures/plant_phenotyping_platform.html), we conducted three trials on three different cultivars (pepper, grapevine, and lettuce) in which we simulated saline and water stress conditions and applied different biostimulants via either foliar or soil application. Gas exchange analyses using either porometry or Infra-Red-Gas-Analysis proved to be the most sensitive in detecting stress onset, although they showed some variability in semi-controlled environments such as greenhouses. Among 3D imaging analyses, the variation in leaf angle proved to be the most sensitive to stress onset. Additionally, increased leaf surface area and digital plant biomass proved highly effective in detecting positive effects induced by biostimulants. Utilizing both 3D imaging technology and analysis of individual leaves, spectroradiometric indexes (Normalised Difference Vegetation Index, Normalized Pigment Chlorophyll ratio Index, Plant Senescence Reflectance Index, Green Leaf Index were less sensitive to stress-level detection, but effective in detecting biostimulant effects under saline stress. The continuous gravimetric method for monitoring plant-atmosphere water fluxes proved to be effective to evaluate plant transpiration in greenhouse and showed less variability than leaf-to-atmosphere gas exchange analyses. Fv/Fm, as determined by fluorescence analysis, was extremely insensitive to stresses. This study has elucidated the advantageous use of available technologies and has identified effective testing strategies for biostimulant product development.ses for assessing biostimulant efficacy under different stress conditions