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Abiotic stresses lead to excessive crop yield losses and are a major threat to agriculture. It is essential to equip crops with multi-stress tolerance to mitigate the adverse effects of abiotic stressors and meet the demands of the increasing global population. The association between plants and symbiotic microorganisms is involved in key functions at the ecosystem and plant levels, and the application of microbial plant biostimulants (MPBs) is a sustainable strategy to augment plant growth and productivity, even under abiotic stress conditions. Several different microorganisms can be used as MPBs to enhance plant growth and produce progressive and reproducible effects on crops. In the present review, we assessed the current knowledge on the use of MPBs, discuss the diversity and characteristics of MPBs, and provide a meticulous assessment of the possible applications of MPBs in abiotic stress relief in crops.

Microbial plant biostimulants have been successfully applied to improve plant growth, stress resilience and productivity. However, the mechanisms of action of biostimulants are still enigmatic, which is the main bottleneck for the fully realization and implementation of biostimulants into the agricultural industry. Here, we report the elucidation of a global metabolic landscape of maize ( Zea mays L) leaves in response to a microbial biostimulant, under well-watered and drought conditions. The study reveals that the increased pool of tricarboxylic acid (TCA) intermediates, alterations in amino acid levels and differential changes in phenolics and lipids are key metabolic signatures induced by the application of the microbial-based biostimulant. These reconfigurations of metabolism gravitate toward growth-promotion and defense preconditioning of the plant. Furthermore, the application of microbial biostimulant conferred enhanced drought resilience to maize plants via altering key metabolic pathways involved in drought resistance mechanisms such as the redox homeostasis, strengthening of the plant cell wall, osmoregulation, energy production and membrane remodeling. For the first time, we show key molecular events, metabolic reprogramming, activated by a microbial biostimulant for plant growth promotion and defense priming. Thus, these elucidated metabolomic insights contribute to ongoing efforts in decoding modes of action of biostimulants and generating fundamental scientific knowledgebase that is necessary for the development of the plant biostimulants industry, for sustainable food security.

Crop production systems have adopted cost-effective, sustainable and environmentally friendly agricultural practices to improve crop yields and the quality of food derived from plants. Approaches such as genetic selection and the creation of varieties displaying favorable traits such as disease and drought resistance have been used in the past and continue to be used. However, the use of biostimulants to promote plant growth has increasingly gained attention, and the market size for biostimulants is estimated to reach USD 4.14 billion by 2025. Plant biostimulants are products obtained from different inorganic or organic substances and microorganisms that can improve plant growth and productivity and abate the negative effects of abiotic stresses. They include materials such as protein hydrolysates, amino acids, humic substances, seaweed extracts and food or industrial waste-derived compounds. Fish processing waste products have potential applications as plant biostimulants. This review gives an overview of plant biostimulants with a focus on fish protein hydrolysates and legislation governing the use of plant biostimulants in agriculture.

The market for seaweed extract biostimulants is experiencing rapid growth, driven by increasing awareness of their benefits and the need for sustainable agricultural practices. This opinion article reviews recent developments in the commercialization of seaweed extract biostimulants, including data on market value and geographical spread, and highlighting the emergence of new species in use. The author advances that recent market trends indicate the start of a gradual transition from wild-harvested to cultivated seaweed sources for biostimulants, while the current proliferation of products is setting the stage for future consolidation of the sector. Challenges to improve market uptake and strategies for companies looking to achieve primacy in the market are discussed.

Food production will have to increase significantly to meet the nutritional needs of the global population. There is also an urgent need to increase the sustainability of food production. Microalgae are a potential sustainable alternative to conventional protein sources and they can also be used in other industries such as agriculture or aquaculture. In this work, the cyanobacterium Arthrospira platensis was produced in Almeria (Spain) in a pilot-scale reactor (80 m2). The biomass produced was used as a protein source and a plant biostimulant following a biorefinery approach. Biomass productivity reached 5.6 g m−2 day−1. The biomass was rich in proteins (67.8 g (100 g)−1) and pigments, namely chlorophyll (7.6 mg (100 g)−1) and phycocyanin (134.2 mg (100 g)−1). An isoelectric solubilisation/precipitation method assisted by ultrasound led to the recovery of a protein extract with a protein content of 91.3 g (100 g)−1. The protein isolate was evaluated as a source of essential amino acids in tagliatelle, leading to an increase in the content of histidine, leucine, lysine, methionine, phenylalanine, threonine, and valine of 36.3, 75.2, 26.3, 30.0, 45.7, 57.8, and 70.0%, respectively. The protein content also increased from 9.6 to 13.9 g (100 g)−1 when the protein isolate was incorporated at a flour substitution level of 4%. The leftovers from the protein extraction were evaluated as plant biostimulants, for which auxin- and cytokinin-like effects were observed. Root development was especially promoted. The results demonstrated the feasibility of producing Spirulina during the winter in Europe and the potential simultaneous use of the biomass as a food ingredient and as a plant biostimulant.

Microalgal exopolysaccharides represent a potential sustainable alternative for the enhancement and protection of agricultural crops including management of both biotic and abiotic stress. In the present study, we investigated the potential of Dunaliella salina exopolysaccharides (PS) to attenuate the effect of salt stress on growth of Solanum lycopersicum, which was grown under different salinity levels (3 and 6 g L−1 NaCl). The effects of PS treatment on plant growth, osmoprotectant molecules, protein content, and antioxidant enzymes activities of tomato plants under salt stress were analyzed. A metabolomics study showed that the exopolysaccharides released by D. salina contained sulfated moiety along with carbohydrates and uronic acids. The application of sulfated exopolysaccharides on tomato plants alleviated the salt stress and mitigated the decrease in length and dry weight of the plant’s shoot and root systems, as well as that of potassium (K+), and K+/Na+ ratio. Furthermore, the increase in proline, phenolic compounds, Na+, and antioxidant enzymes (CAT, POD, SOD) activities caused by salt stress were attenuated after the exopolysaccharide treatment. GC-MS metabolomics analysis showed that PS treatment allowed the activation and/or inhibition of various metabolic pathways involved in the plant’s tolerance to stress such as jasmonic acid-dependent pathways. This study shows the potential of microalgal exopolysaccharides for enhancing tomato tolerance to salt stress and highlights the possibility of their use as plant growth biostimulants under harsh environmental conditions.

Field and laboratory experiments were carried out in 2012–2013, aimed at evaluating the influence of new products stimulating plant growth based on amino acids on crop yield, characteristics of grain and content of macro- and micronutrients in winter wheat (Triticum aestivum L.). The tests included two formulations produced in cooperation with INTERMAG Co. (Olkusz, Poland)—AminoPrim and AminoHort, containing 15% and 20% amino acids, respectively, and 0.27% and 2.1% microelements, respectively. Field experiments showed that the application of products based on amino acids influenced the increase of grain yield of winter wheat (5.4% and 11%, respectively, for the application of AminoPrim at a dose 1.0 L/ha and AminoHort at dose 1.25 L/ha) when compared to the control group without biostimulant. Laboratory tests showed an increase of technological characteristics of grain such as ash content, Zeleny sedimentation index and content of protein. The use of the tested preparations at different doses also contributed to the increase of the nutrients content in grains, in particular copper (ranging 31–50%), as well as sodium (35–43%), calcium (4.3–7.9%) and molybdenum (3.9–16%). Biostimulants based on amino acids, tested in the present study, can be recommended for an efficient agricultural production.

Abiotic and biotic stresses limit the growth and productivity of plants. In the current global scenario, in order to meet the requirements of the ever-increasing world population, chemical pesticides and synthetic fertilizers are used to boost agricultural production. These harmful chemicals pose a serious threat to the health of humans, animals, plants, and the entire biosphere. To minimize the agricultural chemical footprint, extracts of (ANE) have been explored for their ability to improve plant growth and agricultural productivity. The scientific literature reviewed in this article attempts to explain how certain bioactive compounds present in extracts aid to improve plant tolerances to abiotic and/or biotic stresses, plant growth promotion, and their effects on root/microbe interactions. These reports have highlighted the use of various seaweed extracts in improving nutrient use efficiency in treated plants. These studies include investigations of physiological, biochemical, and molecular mechanisms as evidenced using model plants. However, the various modes of action of extracts have not been previously reviewed. The information presented in this review depicts the multiple, beneficial effects of -based biostimulant extracts on plant growth and their defense responses and suggests new opportunities for further applications for marked benefits in production and quality in the agriculture and horticultural sectors.