The effects of EDTA and Trichoderma species on growth and Cu uptake of maize (Zea mays) plants grown in a Cu-contaminated soil.

Metal contamination in soil poses a significant environmental concern worldwide, necessitating effective remediation strategies such as phytoremediation. The present study investigated the effects of EDTA dosage (1.5 and 3 mmol kg-1) and two Trichoderma species (T. harzianum and T. aureoviride) on copper (Cu) content and growth of maize plants grown in a Cu-contaminated soil, as well as Cu fractionation in the soil. In the absence of EDTA, only inoculation with T. harzianum led to a significant increase in shoot biomass. Combining fungal inoculum with EDTA only yielded a significant increase in shoot biomass when using T. aureoviride at a low EDTA rate, highlighting the interplay between fungal species and EDTA rates on plant growth. Results also indicated that EDTA application increased Cu bioavailability, enhancing Cu dissolution and root (not shoot) Cu concentrations. Conversely, inoculation with both Trichoderma species reduced Cu mobility and bioavailability in soil, thereby decreasing the shoot Cu concentrations of plants. When combined with EDTA, only application of T. harzianum resulted in an enhanced shoot Cu concentration, whereas combined application of T. aureoviride and EDTA did not make a significant change compared to the corresponding control (no fungal inoculation, no EDTA), possibly due to a lower compatibility of the T. aureoviride isolate with EDTA. Our results demonstrated that EDTA application, in both non-inoculated and inoculated treatments, increased Cu availability by facilitating its redistribution and transformation from less plant-available fractions (residual, Fe/Mn oxide-bound, and carbonate-bound) to the more readily plant-available forms (water-soluble and exchangeable fractions). In conclusion, although individual Trichoderma application proved beneficial for phytostabilization by reducing Cu content and mitigating Cu toxicity in plants, the combined application of EDTA and a compatible Trichoderma isolate (here, the T. harzianum isolate) holds promise for enhancing the phytoextraction capacity of plants. Although using maize has the advantage of being a food crop, to optimize phytoextraction, plant species with superior metal tolerance and phytoextraction capabilities should be selected, exceeding those of maize.

Phoma medicaginis Isolate Differences Determine Disease Severity and Phytoestrogen Production in Annual Medicago spp.

Phoma black stem and leaf spot disease of annual Medicago spp., caused by Phoma medicaginis, not only can devastate forage and seed yield but can reduce herbage quality by inducing production of phytoestrogens (particularly coumestrol and 4'-O-methylcoumestrol), which can also reduce the ovulation rates of animals grazing infected forage. We determined the consequent phytoestrogen levels on three different annual Medicago species/cultivars (Medicago truncatula cultivar Cyprus, Medicago polymorpha var. brevispina cultivar Serena, and Medicago murex cultivar Zodiac) after inoculation with 35 isolates of P. medicaginis. Across the isolate × cultivar combinations, leaf disease incidence, petiole/stem disease incidence, leaf disease severity, petiole disease severity, and leaf yellowing severity ranged up to 100, 89.4, 100, 58.1, and 61.2%, respectively. Cultivars Cyprus and Serena were the most susceptible and cultivar Zodiac was the most resistant to P. medicaginis. Isolates WAC3653, WAC3658, and WAC4252 produced the most severe disease. Levels of phytoestrogens in stems ranged from 25 to 1,995 mg/kg for coumestrol and from 0 to 418 mg/kg for 4'-O-methylcoumestrol. There was a significant positive relationship of disease incidence and severity parameters with both coumestrol and 4'-O-methylcoumestrol contents, as noted across individual cultivars and across the three cultivars overall, where r = 0.39 and 0.37 for coumestrol and 4'-O-methylcoumestrol, respectively (P < 0.05). Although cultivar Serena was most susceptible to P. medicaginis and produced the highest levels of phytoestrogens in the presence of P. medicaginis, cultivar Zodiac contained the highest levels of phytoestrogens in comparison with other cultivars in the absence of P. medicaginis. There was a 15-fold increase in coumestrol in cultivar Serena but only a 7-fold increase in cultivar Zodiac from infection of P. medicaginis. The study highlights that the intrinsic ability of a particular cultivar to produce phytoestrogens in the absence of the pathogen, and its comparative ability to produce phytoestrogens in the presence of the P. medicaginis, are both important and highly relevant to developing new annual Medicago spp. cultivars that offer improved disease resistance and better animal reproductive outcomes.

Mitigation of Copper Stress in Maize (Zea mays) and Sunflower (Helianthus annuus) Plants by Copper-resistant Pseudomonas Strains.

Use of heavy metal (HM) resistant plant growth-promoting rhizobacteria (PGPR) is among the eco-friendly strategies to increase the resistance of crop plants against the HM stress. In this study, we investigated the effects of two copper (Cu)-resistant PGPR strains (Pseudomonas fluorescens P22 and Pseudomonas sp. Z6) on the growth and nutrition of maize (Zea mays) and sunflower (Helianthus annuus) plants grown in a Cu-contaminated soil under glasshouse conditions. Both PGPR strains significantly increased the plant vegetative parameters including shoot biomass, stem height and diameter, and chlorophyll (SPAD values) index in both crops. In both plants, the PGPR inoculations also significantly elevated the uptake of nutrients including potassium, phosphorus, calcium, magnesium (only by P. fluorescens P22), iron, zinc, manganese, and Cu. Magnitude of the nutritional effects varied between the PGPR strains, e.g., in sunflower, inoculation with P. fluorescens P22 and Pseudomonas sp. Z6 led to an increase in uptake of Zn by 42% and 114%, or Mn by 61% and 88%, respectively, in comparison with control plants. Improved performance of the inoculated plants can be attributed to the plant growth-promoting (e.g., production of auxin and siderophore, phosphate solubilization activities, etc.) and stress removal (e.g., production of ACC-deaminase to drop the ethylene level in stressed plants) properties of the PGPR strains, which were uncovered in our in vitro studies prior to the glasshouse experiment. Beside the plant growth-promoting traits of these PGPR strains, their high resistance to Cu toxicity seemed to be of particular importance for plant fitness improvement under Cu toxicity.

Effects of plant growth-promoting bacteria on EDTA-assisted phytostabilization of heavy metals in a contaminated calcareous soil.

The objective of this research was to determine the combined effects of ethylenediaminetetraacetic acid (EDTA) and plant growth-promoting rhizobacteria (PGPR) on the phytostabilization of Cd, Pb, and Zn by corn and chemical fractionation of these elements in soil. Three heavy metal-resistant bacteria (P18, P15, and P19) were selected. All strains, belonging to the fluorescent pseudomonads, exhibited plant growth-promoting properties, including phosphorus solubilization and production of siderophore, indole acetic acid, and 1-aminocyclopropane-1-carboxylic acid deaminase. Applying EDTA individually or in combination with bacterial strains (P18 and P15) significantly increased shoot biomass. The highest dry shoot biomass was recorded in the combined treatment of EDTA and P15-inoculated pots. Application of EDTA in PGPR-inoculated pots increased concentrations of heavy metals in corn shoots and roots compared to the control. The highest concentration of Zn in corn root and shoot was observed in P15 + EDTA treatment, which were 2.0-fold and 1.3-fold higher than those in the untreated soil. Results of chemical speciation showed that the co-application of EDTA and fluorescent pseudomonads strains increased the bioavailability of Zn, Pb, and Cd by their redistribution from less soluble fractions to water-soluble forms. It was concluded that bacterial inoculation could improve the efficiency of EDTA in phytostabilization of heavy metals from multi-metal contaminated soils.

The effect of Cu-resistant plant growth-promoting rhizobacteria and EDTA on phytoremediation efficiency of plants in a Cu-contaminated soil.

Remediation of heavy metal-contaminated soils is essential for safe agricultural or urban land use, and phytoremediation is among the most effective methods. The success of phytoremediation relies on the size of the plant biomass and bioavailability of the metal for plant uptake. This research was carried out to determine the effect of Ethylenediaminetetraacetic acid (EDTA) ligand and Cu-resistant plant growth-promoting rhizobacteria (PGPR) on phytoremediation efficiency of selected plants as well as fractionation and bioavailability of copper (Cu) in a contaminated soil. The test conditions included three plant species (maize: Zea mays L., sunflower: Helianthus annuus L., and pumpkin: Cucurbita pepo L.) and six treatments, comprising two PGPR strains (Pseudomonas cedrina K4 and Stenotrophomonas sp. A22), two PGPR strains with EDTA, EDTA, and control (without PGPR and EDTA). The combination of EDTA and PGPR enhanced the Cu concentration in both shoot and root tissues and increased the plant biomass. The Cu specific uptake was at a maximum level in the shoots of pumpkin plants when treated with the PGPR strain K4 + EDTA (202 µg pot-1), and the minimum amount of Cu was recorded for sunflower with no PGPR or EDTA addition (29.6 µg pot-1). The result of the PGPR-EDTA treatments showed that the combined application of EDTA and PGPR increased the shoot Cu-specific uptake approximately fourfold in pumpkin. Pumpkin with the highest shoot Cu specific uptake and maize with the highest root Cu specific uptake were the most effective plants in phytoextraction and phytostabilization, respectively. The effectiveness of different PGPR-EDTA treatments in increasing Cu specific uptake by crop plants was assessed by measuring the amount of Cu extracted from the rhizosphere soil adhering to the roots of crop species, by the use of the single extractants Diethylenetriamine pentaacetic acid (DTPA), H2O, NH4NO3, and NH4OAc. PGPR-EDTA treatments increased the amount of water-extractable Cu from rhizosphere soils more than ten times that of the control. The combined application of the EDTA and PGPR reduced the carbonated Fe and Mn oxide-bound Cu in the contaminated soil, and increased the soluble and exchangeable concentration of Cu. Pumpkin, with high shoot biomass and the highest shoot Cu specific uptake was found to be the most effective field crop in phytoextraction of Cu from the contaminated soil. The results of this pot study demonstrated that the EDTA+PGPR treatment could play an important role in increasing the Cu bioavailability and specific uptake by plants, and thus increasing the phytoremediation efficiency of plants in Cu-contaminated areas.

Phytochemical Variations and Enhanced Efficiency of Antioxidant and Antimicrobial Ingredients in Salvia officinalis as Inoculated with Different Rhizobacteria.

Plants produce a variety of secondary metabolites to improve their performance upon exposure to pathogens, pests, herbivores, or environmental stresses. Secondary metabolism in plants is, therefore, highly regulated by presence of biotic or abiotic elicitors in the environment. The present research was undertaken to characterize plant growth-promoting attributes of four plant growth-promoting rhizobacteria (PGPR) including two Pseudomonas fluorescens (Pf Ap1, Pf Ap18) and two P. putida (Pp Ap9, Pp Ap14) strains, and to determine their role (individually or in consortium) on growth of Salvia officialis, and biosynthesis of secondary metabolites such as essential oils (EOs), total phenolics, and flavonoids. The antioxidant and antibacterial properties of the extracts and EOs obtained from the inoculated plants were also investigated. The PGPR inoculum was applied to soil, cuttings, and foliage. Results indicated that different PGPR strains varied in their efficiency for production of auxin, siderophore, 1-aminocyclopropane-1-carboxylate deaminase, and phosphate solubilization. All individually inoculated plants had significantly higher shoot and root biomass, leaf P content, EOs yield, total phenolics, and flavonoids content compared to uninoculated control plants. The major constituents of EOs, cis-thujene, camphor, and 1,8-cineol, increased following inoculation with reference PGPRs. Although the extract from all inoculated plants had improved antioxidant activity, it was remarkable for the Pf Ap18 strain, which had the lowest IC50 value across treatments. Antibacterial assay of various EOs and their major constituents against pathogenic bacteria showed that the highest activity was observed against Staphylococcus aureus using EOs of Pp Ap14 source. Based on our findings, we suggest that individual inoculation with effective PGPR strains can substantially improve plant growth and secondary metabolism in S. officinalis plants.