Phytohormonal basis for the plant growth promoting action of naturally occurring biostimulators

Extracted Eucalyptus globulus Bark Fiber as a Potential Substrate for Pinus radiata and Quillaja saponaria Germination

This study aimed to explore alternative substrates for growing forest species using eucalyptus bark. It evaluated the potential of extracted Eucalyptus globulus fiber bark as a substitute for commercial growing media such as coconut fiber, moss, peat, and compost pine. We determined the physicochemical parameters of the growing media, the germination rate, and the mean fresh and dry weights of seedlings. We used the Munoo-Liisa Vitality Index (MLVI) test to evaluate the phytotoxicity of the bark alone and when mixed with commercial substrates. Generally, the best mixture for seed growth was 75% extracted eucalyptus bark fiber and 25% commercial substrates. In particular, the 75E-25P (peat) mixture is a promising substitute for seedling growth of Pinus radiata, achieving up to 3-times higher MLVI than the control peat alone. For Quillaja saponaria, the best growth substrate was the 50E-50C (coconut fiber) mixture, which had the most significant MLVI values (127%). We added chitosan and alginate-encapsulated fulvic acid phytostimulants to improve the performance of the substrate mixtures. The fulvic acid, encapsulated or not, significantly improved MLVI values in Q. saponaria species and P. radiata in concentrations between 0.05 and 0.1% w/v. This study suggests that mixtures with higher levels of extracted fiber are suitable for growing forest species, thus promoting the application of circular economy principles in forestry.

Potential of carvacrol as plant growth-promotor and green fungicide against fusarium wilt disease of perennial ryegrass

Perennial ryegrass (Lolium perenne L.) is a valuable forage and soil stabilisation crop. Perennial crops have long been associated with good environmental performance and ecosystem stability. Vascular wilt diseases caused by Fusarium species are the most damaging plant diseases affecting both woody perennials and annual crops. Therefore, the aim of the present study was the assessment of the preventive and growth-promoting effects of carvacrol against Fusarium oxysporum, F. solani, and F. nivale (phylogenetically analyzed on the basis of internal transcribed spacer (ITS) regions) causing vascular wilt of ryegrass in vitro and under greenhouse conditions. To accomplish this aim, various parameters were monitored including coleoptile development, rhizogenesis, the incidence of coleoptile lesions, disease index, the visual appearance of ryegrass health, ryegrass organic matter and soil fungal load. The results obtained showed that F. nivale was highly harmful to ryegrass seedlings compared to other Fusarium species. Furthermore, carvacrol with 0.1 and 0.2 mg/mL protected significantly the seedlings against Fusarium wilt diseases both in vitro and in the greenhouse. Simultaneously, carvacrol also functioned as a seedling growth promoter, as is reflected in all monitored parameters, such as the recovery of seedling height and root length, and the development of new leaf buds and secondary roots. Carvacrol proved to be effective plant growth promoter and a bio-fungicide against Fusarium vascular diseases.

Biostimulant Formulations and Moringa oleifera Extracts to Improve Yield, Quality, and Storability of Hydroponic Lettuce

The urgent need to increase the sustainability of crop production has pushed the agricultural sector towards the use of biostimulants based on natural products. The current work aimed to determine whether the preharvest application of two commercial formulations, based on a Fabaceae enzymatic hydrolysate or a blend of nitrogen sources including fulvic acids, and two lab-made aqueous extracts from Moringa oleifera leaves (MLEs), could improve yield, quality, and storability of lettuce grown in a hydroponic system, as compared to an untreated control. Lettuce plants treated with the MLEs showed significantly improved quality parameters (leaf number, area, and color), total phenolic content and antioxidant activity, and resistance against the fungal pathogen Botrytis cinerea, comparable to that obtained with commercial formulates, particularly those based on the protein hydrolysate. A difference between the M. oleifera extracts was observed, probably due to the different compositions. Although further large-scale trials are needed, the tested MLEs seem a promising safe and effective preharvest means to improve lettuce agronomic and quality parameters and decrease susceptibility to rots.

Parametarhizium hingganense, a Novel Ectomycorrhizal Fungal Species, Promotes the Growth of Mung Beans and Enhances Resistance to Disease Induced by Rhizoctonia solani

The mutualistic interactions between mycorrhizae and plants first occurred along with the terrestrialization of plants. The majority of vascular plants are in symbiosis with mycorrhizal fungi. Due to their importance to the economy and ecology, arbuscular mycorrhizal (AM) and ectomycorrhizal (ECM) fungi emerge as the most popular ones. However, the mechanism underlying the beneficial function of ECM fungi is not as clear as AM fungi. Here, the interaction between Parametarhizium hingganense, a novel fungal species isolated from forest litter, and mung bean (Vigna radiata) was studied. P. hingganense demonstrated P solubilization ability in vitro. Treatment of P. hingganense on the seeds resulted in promoted growth with enhanced P content. The hyphae of green fluorescence protein (GFP)-tagged P. hingganense were found to surround the roots and develop between cells, suggesting the establishment of an ectomycorrhizal symbiosis. Upon symbiosis with P. hingganense, the levels of jasmonic acid (JA) and gibberellin (GA₁) and total phenolic and flavonoid content elevated. Meanwhile, damping off caused by Rhizoctonia solani in mycorrhizal plants was alleviated. Taken together, the above findings suggested that symbiosis with P. hingganense conferred growth promotion and priming of defense responses to host plants which should be associated with facilitated P uptake and increased JA and GA₁ levels.

Biofertilizer: The Future of Food Security and Food Safety

There is a direct correlation between population growth and food demand. As the global population continues to rise, there is a need to scale up food production to meet the food demand of the population. In addition, the arable land over time has lost its naturally endowed nutrients. Hence, alternative measures such as fertilizers, pesticides, and herbicides are used to fortify the soil and scale up the production rate. As efforts are being made to meet this food demand and ensure food security, it is equally important to ensure food safety for consumption. Food safety measures need to be put in place throughout the food production chain lines. One of the fundamental measures is the use of biofertilizers or plant growth promoters instead of chemical or synthesized fertilizers, pesticides, and herbicides that poise several dangers to human and animal health. Biofertilizers competitively colonize plant root systems, which, in turn, enhance nutrient uptake, increase productivity and crop yield, improve plants’ tolerance to stress and their resistance to pathogens, and improve plant growth through mechanisms such as the mobilization of essential elements, nutrients, and plant growth hormones. Biofertilizers are cost-effective and ecofriendly in nature, and their continuous usage enhances soil fertility. They also increase crop yield by up to about 10–40% by increasing protein contents, essential amino acids, and vitamins, and by nitrogen fixation. This review therefore highlighted different types of biofertilizers and the mechanisms by which they elicit their function to enhance crop yield to meet food demand. In addition, the review also addressed the role of microorganisms in promoting plant growth and the various organisms that are beneficial for enhancing plant growth.

Coactive role of zinc oxide nanoparticles and plant growth promoting rhizobacteria for mitigation of synchronized effects of heat and drought stress in wheat plants

This study intended to investigate the potential of the plant growth-promoting rhizobacteria (PGPR) and green synthesized zinc oxide nanoparticles (ZnO-NPs) (fruit extract of Papaya) against heat and drought stress in wheat. The characterization of green-synthesized ZnO-NPs was done through UV-vis spectrophotometry, Fourier-transform infrared spectrometry, X-ray diffraction and scanning electron microscopy. Individual and combination of PGPR (Pseudomonas sp.) and ZnO-NPs (10 ppm) amendments were tested in a pot experiment to upregulate wheat defence system under three stress groups (drought, heat and combined heat and drought stress). Drought and heat stress synergistically caused higher damage to wheat plants than individual heat and drought stress. This observation was confirmed with remarkable higher MDA and hydrogen peroxide (H₂O₂) content. Treated plants exposed to all stress groups showed an improved wheat growth and stress resistance through better biomass, photosynthetic pigments, nutrients, soluble sugars, protein and indole acetic acid content. Combination of ZnO-NPs and Pseudomonas sp. Protects the plants from all stress groups by producing higher proline, antioxidant enzymes i. e superoxide dismutase, peroxidase, catalase, ascorbate peroxidase, glutathione reductase and dehydroascorbate reductase, and abscisic acid. Moreover, higher stress alleviation by this treatment was manifested by marked reduced electrolyte leakage, MDA and H₂O₂. The findings of current study confirmed that the synergistic actions of PGPR and ZnO-NPs can rescue plants from both single and combined heat and drought stress.

Plant Growth Promotion by Two Volatile Organic Compounds Emitted From the Fungus Cladosporium halotolerans NGPF1

Microbial volatiles have beneficial roles in the agricultural ecological system, enhancing plant growth and inducing systemic resistance against plant pathogens without being hazardous to the environment. The interactions of plant and fungal volatiles have been extensively studied, but there is limited research specifically elucidating the effects of distinct volatile organic compounds (VOCs) on plant growth promotion. The current study was conducted to investigate the impact of VOCs from Cladosporium halotolerans NGPF1 on plant growth, and to elucidate the mechanisms for the plant growth-promoting (PGP) activity of these VOCs. The VOCs from C. halotolerans NGPF1 significantly promoted plant growth compared with the control, and this PGP activity of the VOCs was culture medium-dependent. Headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography-mass spectrometry (GC-MS) identified two VOC structures with profiles that differed depending on the culture medium. The two compounds that were only produced in potato dextrose (PD) medium were identified as 2-methyl-butanal and 3-methyl-butanal, and both modulated plant growth promotion and root system development. The PGP effects of the identified synthetic compounds were analyzed individually and in blends using N. benthamiana plants. A blend of the two VOCs enhanced growth promotion and root system development compared with the individual compounds. Furthermore, real-time PCR revealed markedly increased expression of genes involved in auxin, expansin, and gibberellin biosynthesis and metabolism in plant leaves exposed to the two volatile blends, while cytokinin and ethylene expression levels were decreased or similar in comparison with the control. These findings demonstrate that naturally occurring fungal VOCs can induce plant growth promotion and provide new insights into the mechanism of PGP activity. The application of stimulatory volatiles for growth enhancement could be used in the agricultural industry to increase crop yield.

Insights into the bacterial community composition of farmed Caulerpa lentillifera: A comparison between contrasting health states

The bacterial communities of Caulerpa lentillifera were studied during an outbreak of an unknown disease in a sea grape farm from Vietnam. Clear differences between healthy and diseased cases were observed at the order, genus, and Operational Taxonomic Unit (OTU) level. A richer diversity was detected in the diseased thalli of C. lentillifera, as well as the dominance of the orders Flavobacteriales (phylum Bacteroidetes) and Phycisphaerales (Planctomycetes). Aquibacter, Winogradskyella, and other OTUs of the family Flavobacteriaceae were hypothesized as detrimental bacteria, this family comprises some well-known seaweed pathogens. Phycisphaera together with other Planctomycetes and Woeseia were probably saprophytes of C. lentillifera. The Rhodobacteraceae and Rhodovulum dominated the bacterial community composition of healthy C. lentillifera. The likely beneficial role of Bradyrhizobium, Paracoccus, and Brevundimonas strains on nutrient cycling and phytohormone production was discussed. The bleaching of diseased C. lentillifera might not only be associated with pathogens but also with an oxidative response. This study offers pioneering insights on the co-occurrence of C. lentillifera-attached bacteria, potential detrimental or beneficial microbes, and a baseline for understanding the C. lentillifera holobiont. Further applied and basic research is urgently needed on C. lentillifera microbiome, shotgun metagenomic, metatranscriptomic, and metabolomic studies as well as bioactivity assays are recommended.

Comparative Genomics Reveals Potential Mechanisms of Plant Beneficial Effects of a Novel Bamboo-Endophytic Bacterial Isolate Paraburkholderia sacchari Suichang626

Plant-beneficial microbes have drawn wide attention due to their potential application as bio-control agents and bio-fertilizers. Moso bamboo, which is among the monocots with the highest growth rate, lives perennially with abundant microbes that may benefit annually growing crops. Genome information of moso bamboo associated bacteria remains underexplored. We isolated and identified a novel Paraburkholderia strain Suichang626 from moso bamboo roots. Growth promoting effects of Suichang626 on both moso bamboo and seedlings of the model dicot Arabidopsis thaliana were documented in laboratory conditions. To gain insight into the genetic basis of this growth promotion effect, we sequenced the genome of Suichang626. Evidenced by genome-wide phylogeny data, we propose that Suichang626 is a novel strain of Paraburkholderia sacchari. Gene homologs encoding biosynthesis of the plant growth-promoting chemicals, acetoin and 2,3-butanediol, were identified in the genome of Suichang626. Comparative genomics was further performed with plant-beneficial and plant/animal pathogenic species of Paraburkholderia and Burkholderia. Genes related to volatile organic compounds, nitrogen fixation, and auxin biosynthesis were discovered specifically in the plant growth-promoting species of both genera.

Sustainable Agriculture Systems in Vegetable Production Using Chitin and Chitosan as Plant Biostimulants

Chitin and chitosan are natural compounds that are biodegradable and nontoxic and have gained noticeable attention due to their effective contribution to increased yield and agro-environmental sustainability. Several effects have been reported for chitosan application in plants. Particularly, it can be used in plant defense systems against biological and environmental stress conditions and as a plant growth promoter—it can increase stomatal conductance and reduce transpiration or be applied as a coating material in seeds. Moreover, it can be effective in promoting chitinolytic microorganisms and prolonging storage life through post-harvest treatments, or benefit nutrient delivery to plants since it may prevent leaching and improve slow release of nutrients in fertilizers. Finally, it can remediate polluted soils through the removal of cationic and anionic heavy metals and the improvement of soil properties. On the other hand, chitin also has many beneficial effects such as plant growth promotion, improved plant nutrition and ability to modulate and improve plants’ resistance to abiotic and biotic stressors. The present review presents a literature overview regarding the effects of chitin, chitosan and derivatives on horticultural crops, highlighting their important role in modern sustainable crop production; the main limitations as well as the future prospects of applications of this particular biostimulant category are also presented.

Ascophyllum nodosum Based Extracts Counteract Salinity Stress in Tomato by Remodeling Leaf Nitrogen Metabolism

Biostimulants have rapidly and widely been adopted as growth enhancers and stress protectants in agriculture, however, due to the complex nature of these products, their mechanism of action is not clearly understood. By using two algal based commercial biostimulants in combination with the Solanum lycopersicum cv. MicroTom model system, we assessed how the modulation of nitrogen metabolites and potassium levels could contribute to mediate physiological mechanisms that are known to occur in response to salt/and or osmotic stress. Here we provide evidence that the reshaping of amino acid metabolism can work as a functional effector, coordinating ion homeostasis, osmotic adjustment and scavenging of reactive oxygen species under increased osmotic stress in MicroTom plant cells. The Superfifty biostimulant is responsible for a minor amino acid rich-phenotype and could represent an interesting instrument to untangle nitrogen metabolism dynamics in response to salinity and/or osmotic stress.

Water Conservation and Plant Survival Strategies of Rhizobacteria under Drought Stress

Drylands are stressful environment for plants growth and production. Plant growth-promoting rhizobacteria (PGPR) acts as a rampart against the adverse impacts of drought stress in drylands and enhances plant growth and is helpful in agricultural sustainability. PGPR improves drought tolerance by implicating physio-chemical modifications called rhizobacterial-induced drought endurance and resilience (RIDER). The RIDER response includes; alterations of phytohormonal levels, metabolic adjustments, production of bacterial exopolysaccharides (EPS), biofilm formation, and antioxidant resistance, including the accumulation of many suitable organic solutes such as carbohydrates, amino acids, and polyamines. Modulation of moisture status by these PGPRs is one of the primary mechanisms regulating plant growth, but studies on their effect on plant survival are scarce in sandy/desert soil. It was found that inoculated plants showed high tolerance to water-deficient conditions by delaying dehydration and maintaining the plant’s water status at an optimal level. PGPR inoculated plants had a high recovery rate after rewatering interms of similar biomass at flowering compared to non-stressed plants. These rhizobacteria enhance plant tolerance and also elicit induced systemic resistance of plants to water scarcity. PGPR also improves the root growth and root architecture, thereby improving nutrient and water uptake. PGPR promoted accumulation of stress-responsive plant metabolites such as amino acids, sugars, and sugar alcohols. These metabolites play a substantial role in regulating plant growth and development and strengthen the plant’s defensive system against various biotic and abiotic stresses, in particular drought stress.

Global Trends in Phytohormone Research: Google Trends Analysis Revealed African Countries Have Higher Demand for Phytohormone Information

The lines of research conducted within a country often reflect its focus on current and future economic needs. Analyzing "search" trends on the internet can provide important insight into predicting the direction of a country in regards to agriculture, health, economy, and other areas. 'Google Trends' collects data on search terms from different countries, and this information can be used to better understand sentiments in different countries and regions. Agricultural output is responsible for feeding the world and there is a continuous quest to find ways to make agriculture more productive, safe, and reliable. The application of phytohormones has been used in agriculture world-wide for many years to improve crop production and continues to be an active area of research for the application in plants. Therefore, in the current study, we searched 'Google Trends' using the phytohormone search terms, abscisic acid, auxins, brassinosteroids, cytokinin, ethylene, gibberellins, jasmonic acid, salicylic acid, and strigolactones. The results indicated that the African country Zambia had the greatest number of queries on auxin research, and Kenya had the most queries in cytokinin and gibberellin research world-wide. For other phytohormones, India had the greatest number of queries for abscisic acid and South Korea had the greatest number of ethylene and jasmonic acid search world-wide. Queries on salicylic acid have been continuously increasing while the least number of queries were related to strigolactones. Only India and United States of America had significant numbers of queries on all nine phytohormones while queries on one or more phytohormones were absent in other countries. India is one of the top five crop-producing countries in the world for apples, millet, orange, potato, pulses, rice, sugarcane, tea, and wheat. Similarly, the United States of America is one of the top five crop-producing countries of the world for apples, grapes, maze, orange, potato, sorghum, sugarcane, and wheat. These might be the most possible factors for the search queries found for all the nine phytohormones in India and the United States of America.

Small Auxin Up RNAs influence the distribution of indole-3-acetic acid and play a potential role in increasing seed size in Euryale ferox Salisb

BACKGROUND

Aquatic Euryale ferox Salisb. is an economically important crop in China and India. Unfortunately, low yield limitations seriously hinder market growth. Unveiling the control of seed size is of remarkable importance in improvement of crops. Here, we generated a new hybrid line (HL) with larger seeds by crossing South Gordon Euryale and North Gordon Euryale (WT) which hasn't been reported before. However, the functional genes and molecular mechanisms controlling the seed size in Euryale ferox Salisb. remain unclear. In this study, we focused on the differentially expressed genes in the auxin signal transduction pathway during fruit development between HL and WT to explore candidate regulatory genes participated in regulating seed size.

RESULTS

Both concentration and localization of indole-3-acetic acid (IAA) at two growth stages of fruits of WT and HL were detected by LC-MS and immunofluorescence. Although IAA content between the two lines did not differ, IAA distribution was significantly different. To elucidate the mechanism and to seek the key genes underlying this difference, RNA-seq was performed on young fruits at the two selected growth stages, and differentially expressed genes related to the auxin transduction pathway were selected for further analysis.

CONCLUSION

Hybrid Euryale ferox Salisb. expressed significant heterosis, resulting in non-prickly, thin-coated, large seeds, which accounted for the significantly larger yield of HL than that of WT. Our study indicated that Small Auxin Up RNAs (SAURs) -mediated localization of IAA regulates seed size in Euryale ferox Salisb. We found that some SAURs may act as a positive mediator of the auxin transduction pathway, thereby contributing to the observed heterosis.

An overview of plant-based natural biostimulants for sustainable horticulture with a particular focus on moringa leaf extracts

The horticulture sector is facing various challenges in the near future. Aside from maintaining or even improving yields, sustainable horticulture production is crucial to achieve food security. Reducing the reliance on agro-chemicals and/or increasing the efficiency of use under a changing climate is crucial. Natural biostimulants can play an important role in this regard, increasing production at a relatively low cost sustainably. Natural biostimulant feedstocks include leaf, root or seed extracts, either individually or in combination with others. Their positive effect on horticultural production is mostly due to plant growth-enhancing bioactive compounds such as phytohormones, amino acids, and nutrients. Here we review recent progress made in research and applications on plant-derived extracts with an emphasis on the use of these renewable biochemicals as biostimulants in sustainable horticulture. Moringa leaf extracts in particular have been shown to improve seed germination, plant growth and yield, nutrient use efficiency, crop and product quality traits (pre- and post-harvest), as well as tolerance to abiotic stresses. Although horticulture production relies on synthetic fertilisers to maintain and improve production, the use of plant-derived biostimulants such as moringa leaf extracts may be an option to reduce quantities needed and thus contribute in achieving global food security sustainably.

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.

P and K Accumulation by Rapeseed as Affected by Biostimulant under Different NPK and S Fertilization Doses

Biostimulants are gaining growing importance among preparations used for plant production. They may cause increasing the effectiveness of nutrient uptake. The aim of the study was to assess P and K accumulation by winter rapeseed after the application of a biostimulant under conditions of varied NPK and S fertilization levels. The field experiment was established on Alfisol, and the factors were: Two levels of NPK fertilization (high 180 N, 70 P, 132 K (kg ha−1) or low 144 N, 35 P, 66 K (kg ha−1)); elementary S fertilization (36 or 0 kg ha−1) and application of seaweed biostimulant or without that treatment. Biostimulant caused an increase in P and K accumulation in the shoots of rapeseed during generative development. Application of biostimulant in rapeseed fertilized with lower NPK rates or not fertilized with S increased P and K accumulation in shoots to the level obtained at higher NPK and S rates without that treatment. Increased level of NPK fertilization caused an increase in P and K accumulation in both shoots and roots at flowering and ripening stages. At the fruit development stage, under higher NPK fertilization there was higher uptake of P and K in rapeseed shoots after presowing fertilization with S.

Gracilaria dura extract confers drought tolerance in wheat by modulating abscisic acid homeostasis

Water stress severely reduces the production of wheat. Application of seaweed extracts have started to show promise in protecting plants from environmental stresses as they contain several biostimulants. However, the modes of action of these biostimulants are not clear. Here, we investigated the role of Gracilaria dura (GD), a red alga, in conferring stress tolerance to wheat during drought under glasshouse and agro-ecological conditions by integrating molecular studies with physiological and field investigations. GD-sap application conferred drought tolerance (as the biomass increased by up to 57% and crop yield by 70%), via facilitating physiological changes associated to maintaining higher water content. GD-sap application significantly increased ABA accumulation (2.34 and 1.46 fold at 4 and 6 days of drought, respectively) due to enhanced expression of biosynthesis genes. This followed an activation of ABA response genes and physiological processes including reduced stomatal opening, thus reducing water loss. Moreover, GD-sap application enhanced the expression of stress-protective genes specifically under water stress. Treatment with fluridone, an ABA inhibitor, further support the role of ABA in GD-sap mediated drought tolerance in wheat. The findings of this study provide insights into the functional role of GD-sap in improving drought tolerance and show the potential to commercialize GD-sap as a potent biostimulant for sustainable agriculture in regions prone to drought.

Efficiency of biogas slurry and Burkholderia phytofirmans PsJN to improve growth, physiology, and antioxidant activity of Brassica napus L. in chromium-contaminated soil

Contamination of soil is a major problem globally with colligated danger for ecosystem and human health. Chromium (Cr) is a toxic heavy metal and caused harmful effect on growth and development of plants. Phytostabilization reduced the mobility of heavy metals with addition of amendments which can significantly decrease metal solubility in soil. Phytostabilization can be achieved by application of biogas slurry (BGS) and endophytic bacteria as amendments in the contaminated soils. The present study revealed that the Burkholderia phytofirmans PsJN and BGS improved the growth, physiology, and antioxidant activity and reduced Cr uptake under a pot experiment spiked with Cr (20 mg kg^-1 soil). The experiment was designed under completely randomized design, four treatments with three replications in normal and Cr-contaminated soil. The inoculation of endophytic bacteria improved the growth and physiology of Brassica. This study showed that the inoculation of endophytic bacteria stabilized the Cr levels in soil and minimized the uptake by the plant shoots and roots in BGS-amended soil. Similarly, activity of antioxidants such as catalase (CAT), reduced glutathione (GSH), glutathione peroxidase (GSH-Px), and glutathione s-transferase (GST) was decreased to normal with combined treatment of BGS and endophytic bacteria in Cr-stressed soil. Overall, the best results were analyzed by combined treatment of BGS and endophytic bacteria to improve growth, physiology, and antioxidant activity of Brassica and immobilize Cr in soil. Moreover, results emphasized the need to use BGS alone or in combination with endophytic bacteria to optimize crop performance, stabilize Cr concentration, and improve environmental efficiency.

Biostimulants in Plant Science: A Global Perspective

This review presents a comprehensive and systematic study of the field of plant biostimulants and considers the fundamental and innovative principles underlying this technology. The elucidation of the biological basis of biostimulant function is a prerequisite for the development of science-based biostimulant industry and sound regulations governing these compounds. The task of defining the biological basis of biostimulants as a class of compounds, however, is made more complex by the diverse sources of biostimulants present in the market, which include bacteria, fungi, seaweeds, higher plants, animals and humate-containing raw materials, and the wide diversity of industrial processes utilized in their preparation. To distinguish biostimulants from the existing legislative product categories we propose the following definition of a biostimulant as "a formulated product of biological origin that improves plant productivity as a consequence of the novel or emergent properties of the complex of constituents, and not as a sole consequence of the presence of known essential plant nutrients, plant growth regulators, or plant protective compounds." The definition provided here is important as it emphasizes the principle that biological function can be positively modulated through application of molecules, or mixtures of molecules, for which an explicit mode of action has not been defined. Given the difficulty in determining a "mode of action" for a biostimulant, and recognizing the need for the market in biostimulants to attain legitimacy, we suggest that the focus of biostimulant research and validation should be upon proof of efficacy and safety and the determination of a broad mechanism of action, without a requirement for the determination of a specific mode of action. While there is a clear commercial imperative to rationalize biostimulants as a discrete class of products, there is also a compelling biological case for the science-based development of, and experimentation with biostimulants in the expectation that this may lead to the identification of novel biological molecules and phenomenon, pathways and processes, that would not have been discovered if the category of biostimulants did not exist, or was not considered legitimate.

Biostimulants in Plant Science: A Global Perspective

This review presents a comprehensive and systematic study of the field of plant biostimulants and considers the fundamental and innovative principles underlying this technology. The elucidation of the biological basis of biostimulant function is a prerequisite for the development of science-based biostimulant industry and sound regulations governing these compounds. The task of defining the biological basis of biostimulants as a class of compounds, however, is made more complex by the diverse sources of biostimulants present in the market, which include bacteria, fungi, seaweeds, higher plants, animals and humate-containing raw materials, and the wide diversity of industrial processes utilized in their preparation. To distinguish biostimulants from the existing legislative product categories we propose the following definition of a biostimulant as "a formulated product of biological origin that improves plant productivity as a consequence of the novel or emergent properties of the complex of constituents, and not as a sole consequence of the presence of known essential plant nutrients, plant growth regulators, or plant protective compounds." The definition provided here is important as it emphasizes the principle that biological function can be positively modulated through application of molecules, or mixtures of molecules, for which an explicit mode of action has not been defined. Given the difficulty in determining a "mode of action" for a biostimulant, and recognizing the need for the market in biostimulants to attain legitimacy, we suggest that the focus of biostimulant research and validation should be upon proof of efficacy and safety and the determination of a broad mechanism of action, without a requirement for the determination of a specific mode of action. While there is a clear commercial imperative to rationalize biostimulants as a discrete class of products, there is also a compelling biological case for the science-based development of, and experimentation with biostimulants in the expectation that this may lead to the identification of novel biological molecules and phenomenon, pathways and processes, that would not have been discovered if the category of biostimulants did not exist, or was not considered legitimate.

Evaluating the use of plant hormones and biostimulators in forage pastures to enhance shoot dry biomass production by perennial ryegrass (Lolium perenne L.)

Fertilisation of established perennial ryegrass forage pastures with nitrogen (N)-based fertilisers is currently the most common practice used on farms to increase pasture forage biomass yield. However, over-fertilisation can lead to undesired environmental impacts, including nitrate leaching into waterways and increased gaseous emissions of ammonia and nitrous oxide to the atmosphere. Additionally, there is growing interest from pastoral farmers to adopt methods for increasing pasture dry matter yield which use 'natural', environmentally safe plant growth stimulators, together with N-based fertilisers. Such plant growth stimulators include plant hormones and plant growth promotive microorganisms such as bacteria and fungi ('biostimulators', which may produce plant growth-inducing hormones), as well as extracts of seaweed (marine algae). This review presents examples and discusses current uses of plant hormones and biostimulators, applied alone or together with N-based fertilisers, to enhance shoot dry matter yield of forage pasture species, with an emphasis on perennial ryegrass.

Mineralization dynamics in soil fertilized with seaweed-fish waste compost

BACKGROUND

Seaweed and fish waste can be composted together to obtain fertilizer with high organic matter and nutrient contents. The nutrients, however, are mostly in organic form and must be mineralized to make them available to plants. The objective of this work was to establish a usage guideline for the compost by studying its mineralization dynamics. Also, the release of inorganic N and C from soil fertilized with the compost was monitored and modelled.

RESULTS

C and N were released throughout the assay, to an extent significantly dependent on fertilizer rate. Mineralization of both elements fitted a first-order exponential model, and each fertilizer rate required using a specific fitting model. An increased rate favoured mineralization (especially of carbon). After 90 days, 2.3% of C and 7.7% of N were mineralized (and 23.3% of total nitrogen made plant available) with the higher rate.

CONCLUSION

C mineralization was slow because organic matter in the compost was very stable. On the other hand, the relatively high initial content in mineral N of the compost increased gradually by the effect of mineralization. The amount of N available would suffice to meet the requirements of moderately demanding crops at the lower fertilizer rate, and even those of more demanding crops at the higher rate.

Enhancing crop yield with the use of N-based fertilizers co-applied with plant hormones or growth regulators

Crop yield, vegetative or reproductive, depends on access to an adequate supply of essential mineral nutrients. At the same time, a crop plant's growth and development, and thus yield, also depend on in situ production of plant hormones. Thus optimizing mineral nutrition and providing supplemental hormones are two mechanisms for gaining appreciable yield increases. Optimizing the mineral nutrient supply is a common and accepted agricultural practice, but the co-application of nitrogen-based fertilizers with plant hormones or plant growth regulators is relatively uncommon. Our review discusses possible uses of plant hormones (gibberellins, auxins, cytokinins, abscisic acid and ethylene) and specific growth regulators (glycine betaine and polyamines) to enhance and optimize crop yield when co-applied with nitrogen-based fertilizers. We conclude that use of growth-active gibberellins, together with a nitrogen-based fertilizer, can result in appreciable and significant additive increases in shoot dry biomass of crops, including forage crops growing under low-temperature conditions. There may also be a potential for use of an auxin or cytokinin, together with a nitrogen-based fertilizer, for obtaining additive increases in dry shoot biomass and/or reproductive yield. Further research, though, is needed to determine the potential of co-application of nitrogen-based fertilizers with abscisic acid, ethylene and other growth regulators.

Exploration of novel rhizospheric yeast isolate as fertilizing soil inoculant for improvement of maize cultivation

BACKGROUND

Chemical input in agriculture is a common practice but makes a serious impact to the environment. In this context, soil isolates having multiple plant growth-promoting (PGP) attributes have been studied. The isolates were tested for their PO4 and Zn solubilization, indole-3-acetic acid (IAA) production and N2 fixation ability. The selected isolate SSm-39 was characterized to molecular level. The isolate SSm-39 was applied to maize cultivation in various combinations with chemical fertilizers. Also, the chemical and microbial status of soil, its effect on maize growth and yield were investigated.

RESULTS

Isolate SSm-39 found most suitable for its PGP attributes and identified as Candida tropicalis. The inoculant (100%) with reduced dose of chemical fertilizer (T5) application notably increased the growth and yield performance of maize. It has improved grain quality by 85% as indicated by carbohydrate and protein content, in comparison to uninoculated control (T3). Soil nutrient status was found to increase twofold with T5 treatment compared with T3 treatment. Enhanced soil nutrient quality supported microbial growth and diversity, thus accelerating soil enzymatic activities.

CONCLUSION

The results validate the multiple PGP traits of C. tropicalis SSm-39, advocating reduction of chemical fertilizer for maize cultivation.

Applications of seaweed extracts in Australian agriculture: past, present and future

A rapidly growing world population has highlighted the need to significantly increase food production in the context of a world with accelerating soil and water shortages as well as climatic stressors. This situation has generated new interest in the application of liquid seaweed extracts because of their potent plant growth-enhancing properties through metabolic benefits, triggering disease response pathways and increasing stress tolerance. The basis for these benefits is complex and poorly understood. Liquid seaweed extracts are complex and have been demonstrated to possess novel mechanisms for increasing crop productivity. The benefits of seaweed extracts to crops have previously been reviewed in the context of the northern hemisphere, but not in the context of Australia, its crops and unique stressors. This review considers the application of seaweed extracts in Australian agriculture by (i) introducing the history of the Australian liquid seaweed extract industry and (ii) focusing on evidence of Australian research related to seaweed extract composition, plant growth properties during plant establishment, pathogenic disease and new approaches to phenotyping the biological efficacy of seaweed extracts. This type of research is essential for future Australian agriculture to develop effective strategies for the use of liquid seaweed extracts.