Bacillus licheniformis FMCH001 Increases Water Use Efficiency via Growth Stimulation in Both Normal and Drought Conditions

Increasing agricultural losses due to biotic and abiotic stresses caused by climate change challenge food security worldwide. A promising strategy to sustain crop productivity under conditions of limited water availability is the use of plant growth promoting rhizobacteria (PGPR). Here, the effects of spore forming Bacillus licheniformis (FMCH001) on growth and physiology of maize (Zea mays L. cv. Ronaldinho) under well-watered and drought stressed conditions were investigated. Pot experiments were conducted in the automated high-throughput phenotyping platform PhenoLab and under greenhouse conditions. Results of the PhenoLab experiments showed that plants inoculated with B. licheniformis FMCH001 exhibited increased root dry weight (DW) and plant water use efficiency (WUE) compared to uninoculated plants. In greenhouse experiments, root and shoot DW significantly increased by more than 15% in inoculated plants compared to uninoculated control plants. Also, the WUE increased in FMCH001 plants up to 46% in both well-watered and drought stressed plants. Root and shoot activities of 11 carbohydrate and eight antioxidative enzymes were characterized in response to FMCH001 treatments. This showed a higher antioxidant activity of catalase (CAT) in roots of FMCH001 treated plants compared to uninoculated plants. The higher CAT activity was observed irrespective of the water regime. These findings show that seed coating with Gram positive spore forming B. licheniformis could be used as biostimulants for enhancing plant WUE under both normal and drought stress conditions.

Some Physiological and Biochemical Mechanisms during Seed-to-Seedling Transition in Tomato as Influenced by Garlic Allelochemicals

The effects of aqueous garlic extracts (AGEs), diallyl disulfide (DADS), and allicin (AAS) were investigated during seed-to-seedling transition of tomato. Independent bioassays were performed including seed priming with AGE (0, 100, and 200 µg∙mL^-1), germination under the allelochemical influence of AGE, DADS, and AAS, and germination under volatile application of AGE. Noticeable differences in germination indices and seedling growth (particularly root growth and fresh weights) were observed in a dose-dependent manner. When germinated under 50 mM NaCl, seeds primed with AGE exhibited induced defense via antioxidant enzyme activities (superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT)), lipid peroxidation (malondialdehyde content (MDA)), and H₂O₂ scavenging. Enzyme-linked immunosorbent analysis (ELISA) of the endogenous phytohormones auxin (IAA), abscisic acid (ABA), cytokinin (ZR), and gibberellic acid (GA₃) in the roots and shoots of the obtained seedlings and the relative expression levels of auxin-responsive protein (IAA2), like-auxin (LAX5), mitogen-activated protein kinase (MAPK7 and MPK2), respiratory burst oxidase homolog (RBOH1), CHI3 and SODCC1 suggested allelopathic functions in stimulating growth responses. Our findings suggest that garlic allelochemicals act as plant biostimulants to enhance auxin biosynthesis and transportation, resulting in root growth promotion. Additionally, the relative expressions of defense-related genes, antioxidant enzymes activities and phytohormonal regulations indicate activation of the defense responses in tomato seedlings resulting in better growth and development. These results, thus, provide a basis to understand the biological functions of garlic allelochemicals from the induced resistance perspective in plants.

Fish By-Product Use as Biostimulants: An Overview of the Current State of the Art, Including Relevant Legislation and Regulations within the EU and USA

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.

Biostimulant Potential of Scenedesmus obliquus Grown in Brewery Wastewater

Microalgae are microorganisms with the capacity to contribute to the sustainable and healthy food production, in addition to wastewater treatment. The subject of this work was to determine the potential of Scenedesmus obliquus microalga grown in brewery wastewater to act as a plant biostimulant. The germination index of watercress seeds, as well as the auxin-like activity in mung bean and cucumber, and in the cytokinin-like activity in cucumber bioassays were used to evaluate the biostimulant potential. Several biomass processes were studied, such as centrifugation, ultrasonication and enzymatic hydrolysis, as well as the final concentration of microalgal extracts to determine their influence in the biostimulant activity of the Scenedesmus biomass. The results showed an increase of 40% on the germination index when using the biomass at 0.1 g/L, without any pre-treatment. For auxin-like activity, the best results (up to 60% with respect to control) were obtained at 0.5 g/L of biomass extract, after a combination of cell disruption, enzymatic hydrolysis and centrifugation. For cytokinin-like activity, the best results (up to 187.5% with respect to control) were achieved without cell disruption, after enzymatic hydrolysis and centrifugation at a biomass extract concentration of 2 g/L.

Quantitative Structure-Activity Relationship of Humic-Like Biostimulants Derived From Agro-Industrial Byproducts and Energy Crops

Humic-like substances (HLSs) isolated by alkaline oxidative hydrolysis from lignin-rich agro-industrial residues have been shown to exert biostimulant activity toward maize (Zea mays L.) germination and early growth. The definition of a quantitative structure-activity relationship (QSAR) between HLS and their bioactivity could be useful to predict their biological properties and tailor plant biostimulants for specific agronomic and industrial uses. Here, we created several projection on latent structure (PLS) regression by using published analytical data on the molecular composition of lignin-derived HLS obtained by both ¹³C-CPMAS-NMR spectra directly on samples and ³¹P-NMR spectra after derivatization of hydroxyl functions with a P-containing reagent (2-chloro-4,4,5,5-tetramethyl-1,3,2-dioxaphospholane). These spectral data were used to model the effect of HLS on the elongation of primary root, lateral seminal roots, total root apparatus, and coleoptile of maize. The ¹³C-CPMAS-NMR data suggested that methoxyl and aromatic moieties positively affected plant growth, while the carboxyl/esterified functions showed a negative impact on the overall seedling development. Alkyl C seems to promote Col elongation while concomitantly reducing that of the root system. Additionally, ³¹P-NMR-derived spectra revealed that the elongation of roots and Col were enhanced by the occurrence of aliphatic hydroxyl groups, and guaiacyl and p-Hydroxyphenyl lignin monomers. The PLS models based on raw dataset from ¹³C-CPMAS-NMR spectra explained more than 74% of the variance for the length of lateral seminal roots, total root system and coleoptile, while other parameters derived from ¹³C-CPMAS-NMR spectra, namely the Hydrophobicity and Hydrophilicity of materials were necessary to explain 83% of the variance of the primary root length. The results from ³¹P-NMR spectra explained the observed biological variance by 90, 96, 96, and 93% for the length of primary root, lateral seminal roots, total root system and coleoptile, respectively. This work shows that different NMR spectroscopy techniques can be used to build up PLS models which can predict the bioactivity of lignin-derived HLS toward early growth of maize plants. The established QSAR may also be exploited to enhance by chemical techniques the bioactive properties of HLS and enhance their plant stimulation capacity.

Plant-Dependent Soil Bacterial Responses Following Amendment With a Multispecies Microbial Biostimulant Compared to Rock Mineral and Chemical Fertilizers

Biostimulants are gaining momentum as potential soil amendments to increase plant health and productivity. Plant growth responses to some biostimulants and poorly soluble fertilizers could increase soil microbial diversity and provide greater plant access to less soluble nutrients. We assessed an agricultural soil amended with a multispecies microbial biostimulant in comparison with two fertilizers that differed in elemental solubilities to identify effects on soil bacterial communities associated with two annual pasture species (subterranean clover and Wimmera ryegrass). The treatments applied were: a multispecies microbial biostimulant, a poorly soluble rock mineral fertilizer at a rate of 5.6 kg P ha^-1, a chemical fertilizer at a rate of 5.6 kg P ha^-1, and a negative control with no fertilizer or microbial biostimulant. The two annual pasture species were grown separately for 10 weeks in a glasshouse with soil maintained at 70% of field capacity. Soil bacteria were studied using 16S rRNA with 27F and 519R bacterial primers on the Mi-seq platform. The microbial biostimulant had no effect on growth of either of the pasture species. However, it did influence soil biodiversity in a way that was dependent on the plant species. While application of the fertilizers increased plant growth, they were both associated with the lowest diversity of the soil bacterial community based on Fisher and Inverse Simpson indices. Additionally, these responses were plant-dependent; soil bacterial richness was highly correlated with soil pH for subterranean clover but not for Wimmera ryegrass. Soil bacterial richness was lowest following application of each fertilizer when subterranean clover was grown. In contrast, for Wimmera ryegrass, soil bacterial richness was lowest for the control and rock mineral fertilizer. Beta diversity at the bacterial OTU level of resolution by permanova demonstrated a significant impact of soil amendments, plant species and an interaction between plant type and soil amendments. This experiment highlights the complexity of how soil amendments, including microbial biostimulants, may influence soil bacterial communities associated with different plant species, and shows that caution is required when linking soil biodiversity to plant growth. In this case, the microbial biostimulant influenced soil biodiversity without influencing plant growth.

Phytomicrobiome Coordination Signals Hold Potential for Climate Change-Resilient Agriculture

A plant growing under natural conditions is always associated with a substantial, diverse, and well-orchestrated community of microbes-the phytomicrobiome. The phytomicrobiome genome is larger and more fluid than that of the plant. The microbes of the phytomicrobiome assist the plant in nutrient uptake, pathogen control, stress management, and overall growth and development. At least some of this is facilitated by the production of signal compounds, both plant-to-microbe and microbe back to the plant. This is best characterized in the legume nitrogen fixing and mycorrhizal symbioses. More recently lipo-chitooligosaccharide (LCO) and thuricin 17, two microbe-to-plant signals, have been shown to regulate stress responses in a wide range of plant species. While thuricin 17 production is constitutive, LCO signals are only produced in response to a signal from the plant. We discuss how some signal compounds will only be discovered when root-associated microbes are exposed to appropriate plant-to-microbe signals (positive regulation), and this might only happen under specific conditions, such as abiotic stress, while others may only be produced in the absence of a particular plant-to-microbe signal molecule (negative regulation). Some phytomicrobiome members only elicit effects in a specific crop species (specialists), while other phytomicrobiome members elicit effects in a wide range of crop species (generalists). We propose that some specialists could exhibit generalist activity when exposed to signals from the correct plant species. The use of microbe-to-plant signals can enhance crop stress tolerance and could result in more climate change resilient agricultural systems.

The Effects of Biostimulants, Biofertilizers and Water-Stress on Nutritional Value and Chemical Composition of Two Spinach Genotypes (Spinacia oleracea L.)

In the present study, the effect of biostimulants application on the nutritional quality and bioactive properties of spinach cultivated in protected environment under water stress conditions was evaluated. For this purpose, four commercially available biostimulant products (Megafol (MEG), Aminovert (AM), Veramin Ca (V), Twin Antistress (TA), and two spinach genotypes (Fuji F1 and Viroflay) were tested under two irrigation regimes (normal irrigation (W+), and water-holding (W–). Fat and carbohydrates content was favored by water stress when Megafol (MEGW+) and Veramin (VW+) were applied on Fuji plants, while calorific value was also increased by MEGW+ treatment. In contrast, protein and ash content increased when AMW– and TAW+ were applied on Viroflay plants. Raffinose and glucose were the most abundant sugars, followed by sucrose and fructose, with the highest contents recorded for Fuji plants when AMW+ (fructose, glucose and total carbohydrates), CW– (sucrose), and TAW– (raffinose) treatments were applied. Regarding organic acids, oxalic and malic acid which had the highest contents for the TAW– (Viroflay plants) and AMW– (Fuji plants) treatments, respectively. α- and γ-tocopherol were the only isoforms detected with MEGW– and VW– inducing the biosynthesis of α-tocopherol, while AMW+ increased γ-tocopherol content in Fuji plants. The main fatty acids were α-linolenic and linoleic acids which were detected in the highest amounts in AMW–, AMW+, and TAW+ the former and in AMW–, VW–, and CW+ the latter. Regarding phenolic compounds content, peak 12 (5,3′,4′-Trihydroxy-3-methoxy-6:7-methylenedioxyflavone-4′-glucuronide) was the most abundant compound, especially in Viroflay plants under normal irrigation and no biostimulants added (CW–). The antioxidant and cytotoxic activity of the tested samples did not show promising results when compared with the positive controls, while a variable antibacterial activity was recorded depending on the tested biostimulant, irrigation regime and genotype. In conclusion, a variable effect of the tested biostimulants and irrigation regimes was observed on bioactive properties and chemical composition of both spinach genotypes which highlights the need for further research in order to make profound conclusions regarding the positive effects of biostimulants under water stress conditions.

Effects of Gellan Oligosaccharide and NaCl Stress on Growth, Photosynthetic Pigments, Mineral Composition, Antioxidant Capacity and Antimicrobial Activity in Red Perilla

The growing market demand for plant raw materials with improved biological value promotes the extensive search for new elicitors and biostimulants. Gellan gum derivatives may enhance plant growth and development, but have never been used under stress conditions. Perilla (Perilla frutescens, Lamiaceae) is a source of valuable bioproducts for the pharmaceutical, cosmetic, and food industries. However, there is not much information on the use of biostimulators in perilla cultivation. In this work we investigated the effects of oligo-gellan and salt (100 mM NaCl) on the yield and quality of red perilla (P. frutescens var. crispa f. purpurea) leaves. Plants grown under stress showed inhibited growth, smaller biomass, their leaves contained less nitrogen, phosphorus, potassium, total polyphenol and total anthocyanins, and accumulated considerably more sodium than control plants. Treatment with oligo-gellan under non-saline conditions stimulated plant growth and the fresh weight content of the above-ground parts, enhanced the accumulation of nitrogen, potassium, magnesium and total polyphenols, and increased antioxidant activity as assessed by DPPH and ABTS assays. Oligo-gellan applied under saline conditions clearly alleviated the stress effects by limiting the loss of biomass, macronutrients, and total polyphenols. Additionally, plants pretreated with oligo-gellan and then exposed to 100 mM NaCl accumulated less sodium, produced greater amounts of photosynthetic pigments, and had greater antioxidant activity than NaCl-stressed plants. Irrespective of the experimental treatment, 50% extract effectively inhibited growth of Escherichia coli and Staphylococcus aureus. Both microorganisms were the least affected by 25% extract obtained from plants untreated with either NaCl or oligo-gellan. In conclusion, oligo-gellan promoted plant growth and enhanced the quality of red perilla leaves and efficiently alleviated the negative effects of salt stress.

Review: Endophytic microbes and their potential applications in crop management

Endophytes are microbes (mostly bacteria and fungi) present asymptomatically in plants. Endophytic microbes are often functional in that they may carry nutrients from the soil into plants, modulate plant development, increase stress tolerance of plants, suppress virulence in pathogens, increase disease resistance in plants, and suppress development of competitor plant species. Endophytic microbes have been shown to: (i) obtain nutrients in soils and transfer nutrients to plants in the rhizophagy cycle and other nutrient-transfer symbioses; (ii) increase plant growth and development; (iii) reduce oxidative stress of hosts; (iv) protect plants from disease; (v) deter feeding by herbivores; and (vi) suppress growth of competitor plant species. Because of the effective functions of endophytic microbes, we suggest that endophytic microbes may significantly reduce use of agrochemicals (fertilizers, fungicides, insecticides, and herbicides) in the cultivation of crop plants. The loss of endophytic microbes from crop plants during domestication and long-term cultivation could be remedied by transfer of endophytes from wild relatives of crops to crop species. Increasing atmospheric carbon dioxide levels could reduce the efficiency of the rhizophagy cycle due to repression of reactive oxygen used to extract nutrients from microbes in roots. © 2019 The Authors. Pest Management Science published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Bioactive properties of greenhouse-cultivated green beans (Phaseolus vulgaris L.) under biostimulants and water-stress effect

BACKGROUND

The scarcity of irrigation water is severely affecting global crop production. In this context, biostimulants are increasingly used as alternatives means against abiotic stress conditions. In this study, phenolic compounds composition and bioactive properties of common bean (Phaseolus vulgaris L.) plants grown under water stress conditions and biostimulants application were investigated.

RESULTS

Sixteen individual phenolic compounds were detected in both pods and seeds with a notable difference in their compositional profile. A significant effect on phenolic compounds content and composition was also observed for the biostimulants tested. Regarding the antibacterial activity, pods of the second harvest and seed extracts showed significant efficacy against Bacillus cereus, especially in water-stressed plants, where all biostimulant treatments were more effective than positive controls. Moreover, all biostimulant treatments for seed extracts of water-stressed plants were more effective against Staphylococcus aureus compared with ampicillin, whereas streptomycin showed the best results. Extracts from pods of the second harvest from normally irrigated plants showed the best results against the fungi tested, except for Penicillium verrucosum var. cyclopium. Finally, no significant cytotoxic effects were detected.

CONCLUSION

In conclusion, the biostimulants tested increased total phenolic compounds content compared with control treatment, especially in pods of the first harvest and seeds of water-stressed plants. Moreover, bioactive properties showed a varied response in regard to irrigation and biostimulant treatment. Therefore, biostimulants can be considered as a useful means towards increasing phenolic compounds content, and they may also affect the antimicrobial properties of pods and seeds extracts. © 2019 Society of Chemical Industry.

Catechol-Loading Nanofibrous Membranes for Eco-Friendly Iron Nutrition of Plants

Modern agriculture requires more efficient and low-impact products and formulations than traditional agrochemicals to improve crop yields. Iron is a micronutrient essential for plant growth and photosynthesis, but it is mostly present in insoluble forms in ecosystems so that it is often limiting for plants. This study was aimed at combining natural strategies and biodegradable nanostructured materials to create environmentally friendly and low-toxic bioactive products capable of both supplying iron to Fe-deficient plants and reducing the impact of agricultural products on the environment. Consequently, free-standing electrospun nanofibrous polycaprolactone/polyhydroxybutyrate thin membranes loaded with catechol (CL-NMs) as an iron-chelating natural agent (at two concentrations) were fabricated on purpose to mobilize Fe from insoluble forms and transfer it to duckweed (Lemna minor L.) plants. The effectiveness of CL-NMs in providing iron to Fe-deficient plants, upon catechol release, tested in duckweeds grown for 4 days under controlled hydroponic conditions, displayed temporal variations in both photosynthetic efficiency and biometric parameters measured by chlorophyll fluorescence and growth imaging. Duckweeds supplied with CL-NMs hosting higher catechol concentrations recovered most of the physiological and growth performances previously impaired by Fe limitation. The absence of short-term toxicity of these materials on duckweeds also proved the low impact on ecosystems of these products.

Corrigendum: Can High Throughput Phenotyping Help Food Security in the Mediterranean Area?

[This corrects the article DOI: 10.3389/fpls.2019.00015.].

Ascophyllum nodosum-Based Biostimulants: Sustainable Applications in Agriculture for the Stimulation of Plant Growth, Stress Tolerance, and Disease Management

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 Ascophyllum nodosum (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 A. nodosum extracts have not been previously reviewed. The information presented in this review depicts the multiple, beneficial effects of A. nodosum-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.

Comprehensive insight into arbuscular mycorrhizal fungi, Trichoderma spp. and plant multilevel interactions with emphasis on biostimulation of horticultural crops

Sustainability and a more environment-friendly approach is an emerging issue relevant to crop production. Abiotic stresses like drought, salinity, heat, cold or heavy metal pollution can severely compromise yields, and in this respect, plant protection practices should be highly efficient as well as safe for the environment and people. Among the many ways to achieve high productivity of healthy, safe and tasty food, the use of beneficial micro-organisms as biostimulants is the most promising one. Two types of soil fungi can be considered efficient natural plants stimulants: arbuscular mycorrhizal fungi (AMF) and Trichoderma spp. (TR). Generally, most investigations indicated AMF and TR were effective, as well as safe, for use as natural biopreparations dedicated to horticultural crops, although some reports pointed to their negative impact on plants. This review focuses on the mutual interaction of AMF and TR, as well as complex relationships with plants analysed on a multidimensional level: biochemical, morphological, ecological and agrotechnical. AMF and TR were found to be effective elicitors of root system development, nutrient uptake, plant stress response and production of secondary metabolites. As natural plant stimulants, beneficial fungi are compatible with modern trends of crop management, environmental conservation and functional food production. Herein, we demonstrate the advantages and disadvantages of AMF and TR use in horticulture and their prospects, as well as the points that need further exploring.

Green Technology: Bacteria-Based Approach Could Lead to Unsuspected Microbe⁻Plant⁻Animal Interactions

The recent and massive revival of green strategies to control plant diseases, mainly as a consequence of the Integrated Pest Management (IPM) rules issued in 2009 by the European Community and the increased consumer awareness of organic products, poses new challenges for human health and food security that need to be addressed in the near future. One of the most important green technologies is biocontrol. This approach is based on living organisms and how these biocontrol agents (BCAs) directly or indirectly interact as a community to control plant pathogens and pest. Although most BCAs have been isolated from plant microbiomes, they share some genomic features, virulence factors, and trans-kingdom infection abilities with human pathogenic microorganisms, thus, their potential impact on human health should be addressed. This evidence, in combination with the outbreaks of human infections associated with consumption of raw fruits and vegetables, opens new questions regarding the role of plants in the human pathogen infection cycle. Moreover, whether BCAs could alter the endophytic bacterial community, thereby leading to the development of new potential human pathogens, is still unclear. In this review, all these issues are debated, highlighting that the research on BCAs and their formulation should include these possible long-lasting consequences of their massive spread in the environment.

Can High Throughput Phenotyping Help Food Security in the Mediterranean Area?

According to the IPCC 2014 report the Mediterranean region will be affected by strong climatic changes, both in terms of average temperature and of precipitations regime. This area hosts some half a billion people and the impact on food production will be severe. To implement a climate smart agriculture paradigm and a sustainable increase of agricultural productivity different approaches can be deployed. Agriculture alone consumes 70% of the entire water available on the planet, thus the observed reduction of useful rainfall and growing costs for irrigation water may severely constrain food security. In our work we focused on two typical Mediterranean crops: durum wheat, a rainfed crop, and tomato, an irrigated one. In wheat we explored the possibility of identifying genotypes resilient to water stress for future breeding aims, while in tomato we explored the possibility of using biostimulants to increase the plant capacity of using water. In order to achieve these targets, we used high throughput phenotyping (HTP). Two traits were considered: digital biovolume, a measure based on imaging techniques in the RGB domain, and Water Use Efficiency index as calculated semi-automatically on the basis of evaporation measurements resulting in a high throughput, non-destructive, non-invasive approach, as opposed to destructive and time consuming traditional methods. Our results clearly indicate that HTP is able to discriminate genotypes and biostimulant treatments that allow plants to use soil water more efficiently. In addition, these methods based on RGB quality images can easily be scaled to field phenotyping structure USVs or UAVs.

Hormonal Effects of an Enzymatically Hydrolyzed Animal Protein-Based Biostimulant (Pepton) in Water-Stressed Tomato Plants

Biostimulants may promote growth or alleviate the negative effects of abiotic stress on plant growth eventually resulting in enhanced yields. We examined the mechanism of action of an enzymatically hydrolyzed animal protein-based biostimulant (Pepton), which has previously been shown to benefit growth and yield in several horticultural crops, particularly under stressful conditions. Tomato plants were exposed to well-watered and water-stressed conditions in a greenhouse and the hormonal profiling of leaves was measured during and after the application of Pepton. Results showed that the Pepton application benefited antioxidant protection and exerted a major hormonal effect in leaves of water-stressed tomatoes by increasing the endogenous content of indole-3-acetic acid (auxin), trans-zeatin (cytokinin), and jasmonic acid. The enhanced jasmonic acid content may have contributed to an increased production of tocochromanols because plastochromanol-8 concentration per unit of chlorophyll was higher in Pepton-treated plants compared to controls. In conclusion, the tested Pepton application may exert a positive effect on hormonal balance and the antioxidant system of plants under water stress in an economically important crop, such as tomato plants.

Enriching Beneficial Microbial Diversity of Indoor Plants and Their Surrounding Built Environment With Biostimulants

Microbial diversity is suggested as the key for plant and human health. However, how microbial diversity can be enriched is largely unknown but of great interest for health issues. Biostimulants offer the way to directly augment our main living areas by the healthy microbiome of indoor plants. Here, we investigated shifts of the microbiome on leaves of spider plants (Chlorophytum comosum) and its surrounding abiotic surfaces in the built environment after irrigation with a vermicompost-based biostimulant for 12 weeks. The biostimulant could not only promote plant growth, but changed the composition of the microbiome and abundance of intact microbial cells on plant leaves and even stronger on abiotic surfaces in close vicinity under constant conditions of the microclimate. Biostimulant treatments stabilized microbial diversity and resulted in an increase of Bacteroidetes and a surprising transient emerge of new phyla, e.g., Verrucomicrobia, Acidobacteria, and Thaumarchaeota. The proportion of potentially beneficial microorganisms like Brevibacillus, Actinoallomurus, Paenibacillus, Sphaerisporangium increased relatively; microbial diversity was stabilized, and the built environment became more plant-like. Detected metabolites like indole-3-acetic acid in the biostimulant were potentially contributed by species of Pseudomonas. Overall, effects of the biostimulant on the composition of the microbiome could be predicted with an accuracy of 87%. This study shows the potential of biostimulants not only for the plant itself, but also for other living holobionts like humans in the surrounding environment.

Effects of Ascophyllum nodosum seaweed extracts on lettuce growth, physiology and fresh-cut salad storage under potassium deficiency

BACKGROUND

Potassium (K) deficiency in leafy vegetables such as lettuce is a major concern regarding quality. Seaweed (SW) extracts, as biostimulants, are biodegradable materials and have become increasingly popular as they are reported to enhance crop growth and yield.

RESULTS

In order to overcome K deficiencies (i.e. 375 vs 125 mg L-1 ), alternative foliar applications with extracts of Ascophyllum nodosum SW or K were examined using lettuce plants which were grown hydroponically. Potassium deficiency (at 125 mg L-1 ) reduced plant biomass, photosynthetic rate, leaf stomatal conductance, lettuce potassium content and tissue antioxidant capacity as compared with the higher K level (375 mg L-1 ). Application of SW increased the relative growth of lettuce in the low-K treatment. The K level and/or SW application altered the plant's enzyme protective activity (superoxide dismutase, SOD; catalase, CAT; peroxidase, POD) against oxidative stress and hydrogen peroxide (H2 O2 ) production. Spray applications of SW mitigated the effects of K deficiency on indicators of enzyme activity and plant damage, back to levels of high K content (375 mg L-1 ). The high K level, but also SW application, increased the antioxidant activity of the processed lettuce before storage. Foliar application of the SW extract increased the quality of cut lettuce grown in 125 mg L-1 K conditions by reducing the rate of respiration and increasing consumer preference.

CONCLUSION

The SW application could alter the detrimental effects of K deficiency during lettuce growth and storage of processed products. © 2018 Society of Chemical Industry.

Response of Wheat to a Multiple Species Microbial Inoculant Compared to Fertilizer Application

Microbial inoculants, including those formed from multiple species, may have dual functions as biostimulants and/or biocontrol agents, and claimed agricultural benefits are instrumental for regulatory categorisation. Biostimulants include commercial products containing substances or microorganisms that stimulate plant growth. Biostimulant microbes can be involved in a range of processes that affect N and P transformations in soil and thus influence nutrient availability, and N and P fertilizers can influence soil microbial diversity and function. A glasshouse experiment was conducted to investigate the effect of a multiple species microbial inoculant relative to a rock-based mineral fertilizer and a chemical fertilizer on wheat growth and yield, and on microbial diversity in the rhizosphere. The microbial inoculant was compared to the mineral fertilizer (equivalent to 5.6 kg N ha-1 and 5.6 kg P ha-1), and to the chemical fertilizer applied at three rates equivalent to: (i) 7.3 kg N ha-1 and 8.4 kg P ha-1 as recommended for on-farm use, (ii) 5.6 kg N ha-1 and 6.5 kg P ha-1 which matched the N in the mineral fertilizer, and (iii) 4.9 kg N ha-1 and 5.6 kg P ha-1 which matched P content in the mineral fertilizer. Despite an early reduction in plant growth, the microbial inoculant treatment increased shoot growth at maturity compared to the control. Similarly, grain yield was higher after application of the microbial inoculant when compared to control, and it was similar to that of plants receiving the fertilizer treatments. Using 16S rRNA sequencing, the microbial inoculant and fertilizer treatments were shown to influence the diversity of rhizosphere bacteria. The microbial inoculant increased the relative abundance of the phylum Actinobacteria. At tillering, the proportion of roots colonized by arbuscular mycorrhizal (AM) fungi increased with the microbial inoculant and mineral fertilizer treatments, but decreased with the chemical fertilizer treatments. At maturity, there were no treatment effects on the proportion of wheat roots colonized by AM fungi. Overall, the multiple species microbial inoculant had beneficial effects in terms of wheat yield relative to the commercial mineral and chemical fertilizers applied at the level recommended for on-farm use in south-western Australia.

Biostimulant Potential of Humic Acids Extracted From an Amendment Obtained via Combination of Olive Mill Wastewaters (OMW) and a Pre-treated Organic Material Derived From Municipal Solid Waste (MSW)

Olive mill wastewaters (OMW) contain significant levels of phenolic compounds with antimicrobial/phytotoxic activity and high amounts of undecomposed organic matter that may exert negative effects on soil biology. Among OMW detoxification techniques, those focusing on oxidative degradation of phenolic compounds are relevant. The composting (bio-oxidation) process in particular, exploits exothermic oxidation reactions by microorganisms to transform the organic matrix of OMW into an amendment biologically stable and feasible to use in agriculture. This process consists of an active phase during which organic compounds are rapidly decomposed, and a curing phase characterized by a slow breakdown of the remaining materials with the formation of humic substances (HS) as by-products. In this study, bio-oxidation of OMW was performed using a pre-treated organic material derived from municipal solid waste (MSW). The obtained amendment (OMWF) was stable and in accordance with the legislative parameters of mixed organic amendments. HS were then extracted from OMWF and MSW (control amendment, Amd-C), and differences in structural properties of their humic acid (HA) fraction were highlighted via spectroscopy (Fourier Transform Infrared) and Dynamic Light Scattering. To assay a potential use of HA as biostimulants for crops, 12-day old Zea Mays L. plants were supplied with HA at 0.5 mg and 1 mg C L-1 for 2 days. HA from both amendments increased plant growth, but HA from OMWF was more effective at both dosages (plus 35-37%). Also, HA from OMWF enhanced both nitrogen assimilation and glycolysis by increasing the activity of nitrate reductase (∼1.8-1.9 fold), phosphoglucose isomerase (PGI) (∼1.8-2 fold) and pyruvate kinase (PK) (∼1.5-1.8 fold), while HA from Amd-C targeted glycolysis preferentially. HA from OMWF, however, significantly stimulated plant nutrition only at lower dosage, perhaps because certain undetermined compounds from detoxified OMW and incorporated in HA altered the root membrane permeability, thus preventing the increase of nutrient uptake. Conversely, HA from Amd-C increased nutrient accumulation in maize at both dosages. In conclusion, our results indicate that the amendment obtained via OMW composting using MSW had a reduced pollution load in terms of phenolic compounds, and HA extracted from OMWF could be used as valuable biostimulants during maize cultivation.

16S rDNA Profiling to Reveal the Influence of Seed-Applied Biostimulants on the Rhizosphere of Young Maize Plants

In an open field trial on two agricultural soils in NW Italy, the impact of two seed-applied biostimulants on the rhizosphere bacterial community of young maize plants was evaluated. The 16S rDNA profiling was carried out on control and treated plant rhizosphere samples collected at the 4-leaf stage and on bulk soil. In both soils, the rhizospheres were significantly enriched in Proteobacteria, Actinobacteria, and Bacteriodetes, while the abundances of Acidobacteria, Cloroflexi and Gemmatimonadetes decreased compared with bulk soil. Among the culturable bacteria genera that showed an increase by both biostimulants, most are known to be beneficial for nutrient uptake, such as Opitutus, Chryseolinea, Terrimonas, Rhodovastum, Cohnella, Pseudoduganella and the species Anaeromyxobacter dehalogenans; others are known to be involved in root growth, such as Niastella, Labrys, Chloroflexia and Thermomonas; or in plant defence, such as Ohtaekwangia, Quadrisphaera, Turneriella, and Actinoallomurus. Both biostimulants were also found to stimulate gen. Nannocystis, a potential biocompetitive agent against aflatoxigenic Aspergillus moulds. Under controlled conditions, both biostimulants enhanced the shoot and root biomass at the 4⁻5 leaf stage. We conclude that the biostimulants do not decrease the biodiversity of the microbial community rhizosphere of young maize plants, but stimulate rare bacterial taxa, some involved in plant growth and pathogen resistance, a result that may have implications in improving crop management.

Biostimulants from food processing by-products: agronomic, quality and metabolic impacts on organic tomato (Solanum lycopersicum L.)

BACKGROUND

Biostimulants have recently gained increased attention due to their multiple benefits for sustainable agriculture. In this study, three food processing by-products - fennel processing residues (FPR), lemon processing residues (LPR) and brewer's spent grain (BSG) - were investigated as potential sources of biostimulants. Their aqueous extracts as individual and associated applications were assessed for their effects on agronomic, quality and metabolic performance of organic tomato in comparison to extract of humic substances (HS) and untreated control (CTRL).

RESULTS

Only FPR extracts stimulated shoot growth and tomato dry matter content, whereas all candidates improved tomato yield. FPR and BSG increased fruit mineral content and BSG-FPR-LPR in combination enhanced titratable acidity. FPR-treated fruits had also 20% more vitamin C than CTRL, and higher phenol content was obtained in those of BSG-LPR. Fruit metabolomic profile showed the tendency of all extracts, except BSG-LPR, to increase tomato citric acid and to decrease β-glucose and methanol concentrations. The analysis revealed accordingly the indispensable role of FPR in combined applications for inducing an HS-like response in fruits.

CONCLUSION

The results were indicative of the biostimulant activity of these extracts and demonstrated them, particularly FPR, as promising candidates for enhancing plant productivity and fruit quality. © 2017 Society of Chemical Industry.

Plant protection means used in organic farming throughout the European Union

Following the obligatory implementation of integrated pest management in the European Union (EU), the plant protection means suitable for application in organic agriculture attracted the attention of quite a wide group of potential users. In spite of the common rules of organic production, as well as the uniform principles of placing plant protection products on the market, the availability of products that can be legally used in organic crop protection differs significantly among the Member States. There is a uniform list of 10 basic substances that can be used in the protection of organic crops throughout the entire EU. Twelve Member States have official registers of plant protection products for use in organic agriculture, and the total number of qualified products per country varies from 11 in Lithuania to 576 in Italy. Some products that improve plant vigour or resistance and may be of use in protection of organic crops are placed on the market as biostimulants. They fall under the law that governs fertilisers and the systems of their registration vary widely among the Member States. In addition, there exist a number of products that have been legally introduced onto the markets of some Member States without registration as a consequence of a loophole in the law. The use of unregistered products in organic agriculture raises some doubts, but currently it seems that there is no legal basis on which to explicitly prohibit the practice. © 2017 Society of Chemical Industry.