Stimulated Root Growth Research Articles

Fire cues trigger germination and stimulate seedling growth of grass species from Brazilian savannas.

Although fire cues (high temperatures and smoke) influence seed germination in numerous species from fire-prone environments, their effects on seed germination of species from neotropical savannas are poorly understood. We exposed seeds of eight grass species from the Cerrado, the Brazilian savanna to heat-shock (80°C or 110°C for 5 min) and/or smoke water, and then set them to germinate in light or dark, at either summer (28°C/18°C) or winter (27°C/14°C) temperature regimes in an incubator. In addition, we evaluated the effects of smoke water on seedling root and shoot growth for four of the species. Smoke interacted with the dark treatment to increase germination from 28% to 93% in Aristida recurvata and 77% to 95% in Aristida riparia. Smoke had no effect on germination of either of these species in the light. Heat-shock alone also promoted seed germination in A. recurvata. For Digitaria lehmanniana, smoke interacted with heat-shock to improve germination from 5% to 16%. In contrast, the fire treatments did not have any effect on the seed germination of the remaining five species. Smoke water stimulated root growth for A. riparia, A. recurvata, and Ctenium cirrosum but had no effect on their shoot growth. The strong promotive effect of smoke on Aristida germination suggests that these species are fire-adapted. Aristida species have an active awn system, which facilitates seed burial, and the smoke and dark interaction would ensure buried seeds germinated post-fire. The species that showed no response to fire cues may either have adapted via alternative strategies or require different concentrations of smoke or levels of heat. This study is one of very few examples showing a positive germination and seedling growth response to smoke for species from neotropical savannas.

Light intensity influence maize adaptation to low P stress by altering root morphology

Soil phosphorus (P) availability, as well as shoot P status, may alter root morphology. However, how root morphological traits to light intensity under various P environments remains unknown. Maize (Zea mays L.) cultivar CD418 grew under nine P application rates (ranged from 0 to 300 mg P kg−1 soil, supplied as KH2PO4) under natural light intensity (NL) and low light intensity (LL, 40% of natural light intensity) in a naturally-lit rain-shed. Plant growth, P uptake, and responses of root morphological traits (i.e. total root length, root surface area, and proportion of <0.2 mm diameter fine root) in the light and P treatments were assessed after 36 d of growth (five-leaf stage). Shoot and root dry weights increased under the natural light intensity in all P treatments. The ratio of root to shoot dry weight increased under NL when the soil Olsen-P was below 15.9 mg kg−1. At relatively low soil P availability (6.7 to 15.9 mg kg−1), total root length, root surface area, and fine root percentage were enhanced with increases in light intensity from LL to NL. These effects diminished in soil with either severely low P (2.6 mg kg−1) or excess P (above 20.6 mg kg−1). Express of the low P-tolerance transcription factor ZmPTF1 (that influences root growth by regulating carbon metabolism in leaves and roots), P uptake, and fertilizer P use efficiency were higher under NL than LL, especially under low P conditions (Olsen-P 6.7–15.9 mg kg−1). Increased responses of root morphological traits to low P conditions were associated with relatively low P concentrations in the leaves and high sucrose concentrations in the roots. Compared to LL, under P deficiency and NL conditions, maize allocated more photosynthates to roots as sucrose, which acts as a low-P signal; in addition, sucrose as a carbon and energy source stimulated root growth and, consequently, adaptation of maize to low P stress.

Tomato Root Growth Inhibition by Salinity and Cadmium Is Mediated By S-Nitrosative Modifications of ROS Metabolic Enzymes Controlled by S-Nitrosoglutathione Reductase.

S-nitrosoglutathione reductase (GSNOR) exerts crucial roles in the homeostasis of nitric oxide (NO) and reactive nitrogen species (RNS) in plant cells through indirect control of S-nitrosation, an important protein post-translational modification in signaling pathways of NO. Using cultivated and wild tomato species, we studied GSNOR function in interactions of key enzymes of reactive oxygen species (ROS) metabolism with RNS mediated by protein S-nitrosation during tomato root growth and responses to salinity and cadmium. Application of a GSNOR inhibitor N6022 increased both NO and S-nitrosothiol levels and stimulated root growth in both genotypes. Moreover, N6022 treatment, as well as S-nitrosoglutathione (GSNO) application, caused intensive S-nitrosation of important enzymes of ROS metabolism, NADPH oxidase (NADPHox) and ascorbate peroxidase (APX). Under abiotic stress, activities of APX and NADPHox were modulated by S-nitrosation. Increased production of H2O2 and subsequent oxidative stress were observed in wild Solanum habrochaites, together with increased GSNOR activity and reduced S-nitrosothiols. An opposite effect occurred in cultivated S. lycopersicum, where reduced GSNOR activity and intensive S-nitrosation resulted in reduced ROS levels by abiotic stress. These data suggest stress-triggered disruption of ROS homeostasis, mediated by modulation of RNS and S-nitrosation of NADPHox and APX, underlies tomato root growth inhibition by salinity and cadmium stress.

A consortium of fungal isolates and biochar improved the phytoremediation potential of Jacaranda mimosifolia D. Don and reduced copper, manganese, and zinc leaching

A consortium of fungal isolates may improve phytoremediation by stimulating root growth whereas biochar reduces metal leaching in contaminated soils. We combined these treatments to evaluate to what extent Jacaranda mimosifolia D. Don seedlings extract metals (Cu, Mn, and Zn) and reduce leaching in soil columns. Contamination treatments were established by combining Cu (200 mg dm−3), Mn (450 mg dm−3), and Zn (450 mg dm−3). A spore suspension of five fungal isolates (Beauveria bassiana, Metarhizium anisopliae, Pochonia chlamydosporia, Purpureocillium lilacinum, and Trichoderma asperella) was sprayed on plant shoots and the soil surface. Biochar (1% m/v) was produced by the pyrolysis of wood sawdust and applied to the soil surface. Finally, control treatments were established in a completely randomized block design. The consortium of fungal isolates increased shoot and root mass, improved the translocation potential of Cu (translocation factor (TF) of 0.25), Mn (TF of 2.93), and Zn (TF of 1.79) from roots to shoots, and increased the total accumulated mass of Mn and Zn in shoots and roots. Biochar applications improved Cu, Mn, and Zn translocation and increased the total accumulated mass of shoot Mn. Moreover, a combination of fungal isolates and biochar increased the translocation factor to 0.44 for Cu, 1.70 for Mn, and 1.34 for Zn relative to the treatment with J. mimosifolia in contaminated soil (CJ); increased shoot Cu concentration; and reduced total leached Cu by a factor of 22.9, Mn by 5.5, and Zn by 22.9 relative to the CJ treatment. A photochemical profile, based on chlorophyll a fluorescence, showed that Jacaranda mimosifolia was tolerant to contaminated soil and is a potential phytoremediator of Cu, Mn, and Zn. Overall, the consortium of fungal isolates and biochar improved the efficiency of phytoremediation by concentrating metals in plant tissue and reducing the risks of leaching.

Removal and Ecotoxicity of 2,4-D and MCPA in Microbial Cultures Enriched with Structurally-Similar Plant Secondary Metabolites

The removal of contaminants from the environment can be enhanced by interactions between structurally-related plant secondary metabolites (PSMs), selected xenobiotics and microorganisms. The aim of this study was to investigate the effect of selected PSMs (ferulic acid—FA; syringic acid—SA) on the removal of structurally-similar phenoxy herbicides (PHs): 2,4-dichlorophenoxyacetic acid (2,4-D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA). The study also examines the biodegradation potential of soil bacteria, based on the occurrence of functional tdfA-like genes, and the ecotoxicity of the samples against two test species: Sinapis alba L. and Lepidium sativum L. The microbial cultures spiked with the PSMs demonstrated higher phenoxy acid removal: 97–100% in the case of 2,4-D and 99%–100% for MCPA. These values ranged from 5% to 100% for control samples not amended with FA or SA. The higher herbicide removal associated with PSM spiking can be attributed to acceleration of the microbial degradation processes. Our findings showed that the addition of SA particularly stimulated the occurrence of the total number of tfdA genes, with this presence being higher than that observed in the unamended samples. PSM spiking was also found to have a beneficial effect on ecotoxicity mitigation, reflected in high (102%) stimulation of root growth by the test species.

Impact of ZnO and ZnS nanoparticles in sewage sludge-amended soil on bacteria, plant and invertebrates

The effect of zinc oxide nanoparticles (ZnO NPs) and zinc sulfide nanoparticles (ZnS NPs) on the toxicity of sewage sludges in sewage sludge-amended soils was investigated with respect to plant- (Lepidium sativum) and soil- (Folsomia candida) species. The toxicity of porewater obtained from the tested soils towards Vibrio fischeri (Microtox®) was also investigated. Two sewage sludges (SSL1 and SSL2) with different organic matter content were amended with nanoparticles. Depending on the type of biotest and the type of sewage sludge, different effects of ZnO or ZnS NPs on the toxicity of sewage sludge-amended soil were observed. In general, ZnO and ZnS NPs stimulated root growth for SSL1 or reduced the harmful impact of SSL2 on the root growth of L. sativum roots. Greater stimulation or inhibition of root growth was observed for the ZnO than ZnS NPs. The unfavorable effect of ZnO/ZnS NPs on F. candida mortality and reproduction was observed at a concentration of ZnO/ZnS in sewage sludge ≥250 mg/kg. Generally, there were no significant differences between ZnO and ZnS NPs toxicity towards F. candida. Aging for 45 days of sewage sludge-amended soil containing NPs affected ZnO and ZnS NPs toxicity to all tested organisms. In the most cases, the toxicity decreased after 45 days of aging for plant (L. sativum) and invertebrates (F. candida). The toxicity of porewater to V. fischeri from sewage sludge-amended soil contains ZnO NPs did not change, while in the case of ZnS NPs, the toxicity increased after 45 days of aging.

PHYTOTOXIC ACTIVITY REDUCTION ASSESSMENT OF COPPER IONS THROUGH THE ONION APICAL MERISTEM

This paper investigates the protective properties of the aqueous extract of silkworm pupae (CABG) in terms of the toxic effect of copper ions on morphometrically parameters in Allium-test. Methods: It is established that the joint use of aqueous extract of silkworm pupae and copper sulphate at a concentration of 100 µm growth inhibition of roots is not happening and even stimulated by the application of aqueous extract of silkworm pupae at a concentration of 1 ml/10 ml. Stimulation of root growth is also observed with the combined use of 1000 µm copper sulfate and aqueous extract of silkworm pupae in a concentration of 10 ml/100 ml of the solution with respect to the use of copper sulfate only. A significant decrease in the parameter ‘length of sprouts' in 1.3-6.0 times with respect to the control was observed when using copper ions in concentrations of 100-1000 microns, while at a metal concentration of 10 microns no negative effect on the development of sprouts was established. The emergence of lateral roots in 20-50% of cases observed only in the use of aqueous extract of silkworm pupae. Thus, in the study of morphometric parameters of seedlings of onion (the relative growth of roots, length of shoots, their weight) set the modifier of the protective effect of aqueous extract of silkworm pupae when used together with copper sulfate in concentrations of 10 and 100 µm. At a concentration of 10 ml of aqueous extract of silkworm pupae/100 ml solution protective function in relation to ions of copper are more severe.

Exogenous N-Acetylcysteine alleviates heavy metal stress by promoting phenolic acids to support antioxidant defence systems in wheat roots

N-acetylcysteine (N-Acetyl L-cysteine, NAC) is a thiol compound derived from the addition of the acetyl group to cysteine amino acid. NAC has been used as an antioxidant, free radical scavenger, and chelating agent for reducing the deleterious effects on plants of biotic and abiotic environmental stresses. It can also relieve heavy metal (HM) toxicity, although its alleviating mechanism remains unknown. In this study, we compared HM-stressed (Cu, Hg, Cd and Pb, 100 μM each) wheat seedlings without NAC treatment and in combination with NAC (1 mM). In comparison to HMs alone, NAC treatment in combination with HMs (Cu, Cd, Hg and Pb, respectively) stimulated root growth (1.1-, 1.5-, 10.5- and 1.9-fold), and significantly increased fresh (1.3-, 1.5-, 4.3- and 1.4-fold) and dry (1.2-, 1.5-, 2.5- and 1.2-fold) mass. Combination treatment also led to significant reductions in HM concentrations (1.3-, 1.4-, 4- and 1.1-fold, respectively). GSH (1.1 – 1.8-fold), TBARS (1.4 – 2.7-fold) and H2O2 (1.6 – 1.8-fold) contents in treatment with HMs alone were significantly mitigated by the NAC combination. Some of the antioxidant enzyme activities increased or reduced by some HM treatments alone were stimulated by a combination of NAC with HMs, or remained unchanged or changed only insignificantly, supported by the phenolic pool of the plant. Ferulic, p-comaric and syringic acids were the major phenolic acids (PAs) in the roots in free, ester, glycoside and ester-bound forms, and their concentrations were increased by HM treatments alone, in comparison to the control seedlings, while PAs concentrations were relatively reduced by NAC in combination with HMs. These results indicate that NAC can alleviate HM toxicity and improve the growth of HM-stressed wheat seedlings by coordinated induction of the phenolic pool and the antioxidant defence system.

The effects of IBA on the composition of maize root cell walls

Auxin is one of the crucial plant hormones which stimulates and controls cell and plant growth. The effects of auxin IBA (indole-3-butyric acid) during 10-days on maize plants growth in controlled conditions (hydroponic, 16-h photoperiod, 70% humidity, 25/20 °C temperature), depended on its concentration in the substrate. A high concentration (10−7 M) of IBA inhibited root growth, evoked the development of apoplasmic barriers (Casparian bands and suberin lamellae) closer to the root apex, and elevated the amount of lignin in roots. A low concentration (10-11 M) of IBA stimulated root growth but affected neither the development of apoplasmic barriers, nor the amount of lignin. Auxin in a 10-8 M concentration influenced the root growth to a minimal extent compare to the control, and it was the non-effective concentration. Plant cell walls as cell structures ensure cell enlargement and plant growth, and have to react to auxin stimulus by modification of their components. We found the most significant changes in the composition of the PF III fraction (lignocellulosic complex) of the cell wall. The presence of auxin in the substrate affected all three components of this fraction - Klason lignin and both the by acid (2 M TFA) non-hydrolysable and the hydrolysable parts of this complex. The ratio of the non-hydrolysable part to the Klason lignin increased from 1.3 to 3.3 with increasing auxin concentrations in the substrate. This may be related to the deposition of polysaccharides and lignin in the cell wall, which help maintain the specific tensile stress of, and turgor pressure on, the cell walls.

Rhizobacterial treatments of tall fescue and bermudagrass increases tolerance to damage from white grubs.

Inoculation of hybrid bermudagrass with plant growth-promoting rhizobacteria (PGPR) can increase plant growth and influence relationships with above-ground herbivores like fall armyworms. However, few experiments have evaluated PGPR applications relative to root herbivory. Root-feeding white grubs cause severe damage to grasses, especially in tall fescue pastures, golf courses, and lawns. Since bacterial inoculants enhance root growth, the goal of this study was to determine if the inoculation of hybrid bermudagrass by rhizobacteria can increase the tolerance of tall fescue and hybrid bermudagrass to damage from white grub feeding, and if PGPR are compatible with neonicotinoid insecticides commonly used for white grub control. In trials with tall fescue and hybrid bermudagrass, grasses were treated with the PGPR strain mixture Blend 20 or nitrogen or left non-treated and were then infested with Japanese beetle grubs. Grasses treated with PGPR and nitrogen fertilizer produced significantly more top growth than the non-treated grub-infested controls. Tall fescue and hybrid bermudagrass treated with Blend 20 produced root mass similar to or greater than nitrogen fertilized grasses. Both grasses treated with Blend 20 had greater root mass than non-treated infested grass. No treatment negatively impacted grub survival, and weight gains of grubs were similar for all treatments. Bacterial strains were typically compatible with insecticides used to control white grubs. PGPR and nitrogen fertilization stimulate root growth resulting in tolerance of tall fescue and hybrid bermudagrass to white grub infestation. PGPR, acting as biostimulants to increase root biomass on grasses, may have utility for IPM of root herbivores. © 2019 Society of Chemical Industry.

Assessment of the Potential of Indole-3-Acetic Acid Producing Bacteria to manage Chemical Fertilizers Application

Indole-3-acetic acid (IAA) has a vital role in stimulation of root growth and nutrients acquisition from soil. The study was conducted to isolate rhizospheric (R) and endophytic (E) IAA producer bacteria from the rhizosphere soil and surface sterilized root of wheat, and evaluate the effects of isolates to managing of chemical fertilizers application. For this, we examined the influence of different chemical fertilizer application rates (40, 60, 80 and 100%) coupled with R (Bacillus toyonensis) and E (Pseudomonas mosselii) IAA producer bacteria on wheat growth. Results indicated that supplementing 80% of the recommended chemical fertilizers rate with E isolates resulted in increase of wheat growth indices, which were similar to 100%-fertilizer need without bacterial inoculant. It seems that application of reduced chemical fertilizers integrated with IAA producer bacteria can positively affect the plant growth and led to decrease of chemical fertilizers application. Then optimal condition for IAA release was determined by P. mosselii and B. toyonensis. Results revealed that optimal growth medium conditions for isolates defined to be at l-tryptophan concentration of 3.0 mg mL−1 at 96 h of incubation and 32 °C by spectrophotometry. Increase in l-tryptophan concentration (> 3.0 mg m−1) significantly decreased the IAA production. These results could be attributed to a possible inhibition towards the indigenous (and/or exogenous) soil microbial population by the higher concentrations of l-tryptophan. Glucose used as carbon source, gave the most IAA production (22.9 μg mL−1) in E isolate. About R isolate use of sucrose in the medium culture stimulates IAA production.

Endophytic fungus Beauveria bassiana can enhance drought tolerance in red oak seedlings

Endophytic fungus, usually treated as an entomopathogenic agent, can provide drought stress tolerance to red oak seedlings. Its effect is realized through root growth stimulation. Endophytic fungi are known to be active in the plant environmental stress alleviation. In this work, we proved the ability of endophytic Beauveria bassiana, which is almost exclusively treated as an entomopathogenic fungus, in mitigating drought stress in dehydrated red oak (Quercus rubra L.) seedlings. Despite small differences between experiments, in general, leaf relative water content and stomatal conductance were less reduced (ca. 50% and 15%, respectively), free proline did not accumulate over the control level, carbon isotope 13C discrimination/water use efficiency was not affected and root growth was stimulated at a similar plant transpiration area in the endophyte-colonised individuals. Regression analysis revealed that the root growth stimulation provided by the fungus under drought had the most important effect on their water status.

Transcript and metabolic adjustments triggered by drought in Ilex paraguariensis leaves.

Abscisic acid is involved in the drought response of Ilex paraguariensis. Acclimation includes root growth stimulation, stomatal closure, osmotic adjustment, photoprotection, and regulation of nonstructural carbohydrates and amino acid metabolisms. Ilex paraguariensis (yerba mate) is cultivated in the subtropical region of South America, where the occurrence of drought episodes limit yield. To explore the mechanisms that allow I. paraguariensis to overcome dehydration, we investigated (1) how gene expression varied between water-stressed and non-stressed plants and (2) in what way the modulation of gene expression was linked to physiological status and metabolite composition. A total of 4920 differentially expressed transcripts were obtained through RNA-Seq after water deprivation. Drought induced the expression of several transcripts involved in the ABA-signalling pathway. Stomatal closure and leaf osmotic adjustments were promoted to minimize water loss, and these responses were accompanied by a high transcriptional remodeling of stress perception, signalling and transcriptional regulation, the photoprotective and antioxidant systems, and other stress-responsive genes. Simultaneously, significant changes in metabolite contents were detected. Glutamine, phenylalanine, isomaltose, fucose, and malate levels were shown to be positively correlated with dehydration. Principal component analysis showed differences in the metabolic profiles of control and stressed leaves. These results provide a comprehensive overview of how I. paraguariensis responds to dehydration at transcriptional and metabolomic levels and provide further characterization of the molecular mechanisms associated with drought response in perennial subtropical species.

Effects of selenite on the growth of alfalfa (Medicago sativa L. cv. Sadie 7) and related physiological mechanisms

Selenium (Se) is indispensable to animals. The aims of this study were to explore the threshold dose of Se application in soil and reveal the mechanism of selenite effect on alfalfa growth, which is important for producing Se-enriched forage. Pot experiments were carried out in a greenhouse to explore the physiological mechanisms that are related to the response of forage crop to Se application. Alfalfa plants were treated with different Se levels (Se as Na2SeO3 dissolved in water was evenly sprinkled on the soil) to determine the effects of selenite supply on antioxidant activity, photosynthetic parameters, root activities, and the absorption of essential elements of alfalfa. Compared with the control plants, those treated with 5 and 10 mg kg−1 Se exhibited increased shoot Se concentrations by 4.5- and 8.1-fold, respectively. The Se partitioning factors for alfalfa ranged from 0.47 to 0.89. The dry weights of roots and whole plants reached maximum values after applying 1 mg kg−1 Se. At 20 mg kg−1 Se, the plant growth, antioxidant enzyme activity, photosynthetic parameters, root activity, and P and K absorption were inhibited. Alfalfa growth was not negatively affected by Se application less than 20 mg kg−1. Low-dose selenite (0.5 and 1 mg kg−1 Se) stimulated plant growth, mainly due to the stimulation of root growth by enhancing root activities and therefore promoting the absorption of P, K, Ca, Fe, and Mn. The increase in antioxidant enzyme activity and net photosynthetic rate partially resulted from the increased carotenoid content, which also contributed to the increasing dry matter at low-dose selenite levels. Given the relatively high transport efficiency of Se from root to overground part, alfalfa can be potentially used in the production of Se-enriched forage, and 10 mg kg−1 Se is the optimum reference dose of Se application in soil.

Effects of free‐air CO2 enrichment and drought on root growth of field grown maize and sorghum

AbstractIncreasing CO2 concentration ([CO2]) is thought to induce climate change and thereby increase air temperatures and the risk of drought stress, the latter impairing crop growth. The objective of this study was to investigate the effects of elevated [CO2] and drought stress on root growth of one maize genotype (Zea mays cv. Simao) and two sorghum genotypes (Sorghum bicolor cv. Bulldozer and Sorghum bicolor × Sorghum sudanense cv. Inka) under the cool moderate climate of Central Europe. It was hypothesized that root growth stimulation due to elevated [CO2] compensates for a reduced root growth under drought stress. Therefore, we established an experiment within a free‐air carbon dioxide enrichment system (FACE) in 2010 and 2011. Sorghum and maize genotypes were grown under ambient [CO2] (385 ppm CO2) and elevated [CO2] (600 ppm CO2) and in combination with restricted and sufficient water supply. Elevated [CO2] decreased root length density (RLD) in the upper soil layers for all genotypes, but increased it in deeper layers. Higher [CO2] enhanced specific root length (SRL) of “Simao” and “Bulldozer,” however, did not affect that of “Inka.” “Simao” achieved a higher SRL than the sorghum genotypes, indicating an efficient investment in root dry matter. Although elevated [CO2] affected the root growth, no interaction with the water treatment and, consequently, no compensatory effect of elevated [CO2] could be identified.

Beneficial and Pathogenic Arabidopsis Root-Interacting Fungi Differently Affect Auxin Levels and Responsive Genes During Early Infection.

Auxin (indole-3-acetic acid, IAA) is an important phytohormone involved in root growth and development. Root-interacting beneficial and pathogenic fungi utilize auxin and its target genes to manipulate the performance of their hosts for their own needs. In order to follow and visualize auxin effects in fungi-colonized Arabidopsis roots, we used the dual auxin reporter construct DR5::EGFP-DR5v2::tdTomato and fluorescence microscopy as well as LC-MS-based phytohormone analyses. We demonstrate that the beneficial endophytic fungi Piriformospora indica and Mortierella hyalina produce and accumulate IAA in their mycelia, in contrast to the phytopathogenic biotrophic fungus Verticillium dahliae and the necrotrophic fungus Alternaria brassicicola. Within 3 h after exposure of Arabidopsis roots to the pathogens, the signals of the auxin-responsive reporter genes disappeared. When exposed to P. indica, significantly higher auxin levels and stimulated expression of auxin-responsive reporter genes were detected both in lateral root primordia and the root elongation zone within 1 day. Elevated auxin levels were also present in the M. hyalina/Arabidopsis root interaction, but no downstream effects on auxin-responsive reporter genes were observed. However, the jasmonate level was strongly increased in the colonized roots. We propose that the lack of stimulated root growth upon infection with M. hyalina is not caused by the absence of auxin, but an inhibitory effect mediated by high jasmonate content.

Effects of green seaweed extract on Arabidopsis early development suggest roles for hormone signalling in plant responses to algal fertilisers

The growing population requires sustainable, environmentally-friendly crops. The plant growth-enhancing properties of algal extracts have suggested their use as biofertilisers. The mechanism(s) by which algal extracts affect plant growth are unknown. We examined the effects of extracts from the common green seaweed Ulva intestinalis on germination and root development in the model land plant Arabidopsis thaliana. Ulva extract concentrations above 0.1% inhibited Arabidopsis germination and root growth. Ulva extract <0.1% stimulated root growth. All concentrations of Ulva extract inhibited lateral root formation. An abscisic-acid-insensitive mutant, abi1, showed altered sensitivity to germination- and root growth-inhibition. Ethylene- and cytokinin-insensitive mutants were partly insensitive to germination-inhibition. This suggests that different mechanisms mediate each effect of Ulva extract on early Arabidopsis development and that multiple hormones contribute to germination-inhibition. Elemental analysis showed that Ulva contains high levels of Aluminium ions (Al3+). Ethylene and cytokinin have been suggested to function in Al3+-mediated root growth inhibition: our data suggest that if Ulva Al3+ levels inhibit root growth, this is via a novel mechanism. We suggest algal extracts should be used cautiously as fertilisers, as the inhibitory effects on early development may outweigh any benefits if the concentration of extract is too high.

Hormetic UV‐C seed treatments for the control of tomato diseases

Hormesis is a dose response phenomenon in which low, non‐damaging doses of a stressor bring about a positive response in the organism undergoing treatment. Evidence is provided here that hormetic UV‐C treatments of tomato seed can control disease caused by Botrytis cinerea, Fusarium oxysporum f. sp. lycopersici (FOL) and f. sp. radicis‐lycopersici (FORL) on tomato (Solanum lycopersicum). Treating seeds with a 4 kJ m−2 dose of UV‐C significantly reduced both the disease incidence and progression of B. cinerea, with approximately 10% reductions in both on cv. Shirley. Disease severity assays for FOL and FORL on cv. Moneymaker showed dose‐dependent responses: UV‐C treatments of 4 and 6 kJ m−2 significantly reduced the disease severity scores of FOL, whilst only the 6 kJ m−2 showed significant reductions for FORL. To determine the effects of treatment on germination and seedling growth, UV‐C doses of 4, 8 and 12 kJ m−2 were performed on cv. Shirley. No negative impacts on germination or seedling growth were observed for any of the treatments. However, the 8 kJ m−2 treatment showed significant biostimulation, with increases in seedling, root and hypocotyl dry weight of 11.4%, 23.1% and 12.0%, respectively, when compared to the control. Furthermore, significant increases in the root‐mass fraction (10.6%) and root:shoot ratio (13.1%) along with a decrease in shoot‐mass fraction (2.0%) indicates that the 8 kJ m−2 treatment stimulated root growth to the greatest extent. There was no effect on hypocotyl and primary root length or the number of lateral roots, indicating no adverse effects to basic root architecture or seedling growth.

The Form of N Supply Determines Plant Growth Promotion by P-Solubilizing Microorganisms in Maize.

Phosphate-(P)-solubilizing microorganisms (PSM) are important drivers of P cycling in natural and agro-ecosystems. Their use as plant inoculants to improve P acquisition of crops has been investigated for decades. However, limited reproducibility of the expected effects, particularly under field conditions, remains a major challenge. This study demonstrates that the form of nitrogen fertilization has a significant impact on the performance of various fungal and bacterial PSM inoculants in maize grown on neutral to alkaline soils with limited P availability. Under these conditions, a high soil pH-buffering capacity frequently limits the efficiency of nutrient mobilization, mediated by plant roots and microorganisms via rhizosphere acidification. In a soil pH range between 7.0 and 8.0, nitrate fertilization promoting rhizosphere alkalinisation further aggravates this problem. Accordingly, in greenhouse experiments, six strains of Pseudomonas, Bacillus, Paenibacillus, Streptomyces, and Penicillium with proven P-solubilizing potential, completely failed to promote P acquisition in maize grown on a calcareous Loess sub-soil pH 7.6 with nitrate fertilization and rock phosphate (Rock-P) as a sparingly soluble P source. However, after replacement of nitrate fertilization by ammonium, stabilized with the nitrification inhibitor 3,4-dimethylpyrazole-phosphate (DMPP), five out of seven investigated PSM inoculants (comprising 12 fungal and bacterial PSM strains) exerted beneficial effects on plant growth and reached up to 88% of the shoot biomass production of a control supplied with soluble triple-superphosphate (TSP). Stabilized ammonium combined with PSM-inoculants improved P acquisition (Trichoderma harzianum T22, Pseudomonas sp. DMSZ 13134), while other strains particularly stimulated root growth (T. harzianum OMG16, Bacillus amyloliquefaciens FZB42), which promoted the acquisition also of other mineral nutrients, such as N, K, and Mn. A similar effect was recorded under field conditions on an alkaline clay-loam soil pH 8.6. The combination of stabilized ammonium with a range of consortium products based on T. harzianum OMG16, B. amyloliquefaciens, micronutrients, and humic acids completely compensated the effect of a TSP fertilization on field establishment, nutrient acquisition, and yield formation in maize, while non-stabilized urea-di-ammonium phosphate fertilization was largely ineffective. These findings suggest that the efficiency of PSM-plant interactions can be influenced by the form of N fertilization, offering promising perspectives for synergistic effects with stabilized ammonium fertilizers.

Leaf and Root Allelopathic Potential of the Vernonanthura brasiliana

ABSTRACT: The Brazilian native weed assa-peixe (Vernonanthura brasiliana) is considered one of the main invasive plant species of pasture areas in the Amazon. It is thus necessary to know their biology and their behavior in the environment, and to enhance the development of management strategies, minimizing the use of herbicides. The objective of this study was to test the allelopathic effect on the germination and growth of the bioindicator species Lactuca sativa from leaf and root extracts obtained from fresh and dry V. brasiliana. The experiment consisted of six treatments with concentrations of 0, 12.5, 25, 50, 100, and 200 mg mL-1, using four replicates per treatment. The evaluated parameters were: germination percentage, first count, germination speed index, and shoot and root length. The aqueous extract of fresh V. brasiliana roots caused an allelopathic effect on all evaluated parameters, while the dry root extract only affected the germination speed index. Root growth inhibition and growth stimulation of lettuce seedlings were verified when submitted to dry and fresh root extracts. Extracts of V. brasiliana caused an allelopathic effect on the species Lactuca sativa L., where the aqueous extracts of dry leaves and fresh roots were the most influential.