Combined bio-chemical fertilizers ameliorate agro-biochemical attributes of black cumin (Nigella sativa L.)

Phytoremediation of mercury-contaminated Soil by Vigna radiata L. plant in companion with bacterial and fungal biofertilizers

Mercury is one of the most toxic pollutants that has drawn the attention of scientists. This study investigates the phytoremediation capabilities of Vigna radiata L. in conjunction with microbial biostimulators. The inoculated seeds were cultivated in soil under controlled greenhouse conditions. The concentration of Hg, biomass, and photosynthetic pigments was investigated under amendment factor including EDTA, bacterial, fungal (Mycorrhiza and Trichoderma), biochar, and combined levels, as well as the pollution factor with three levels of HgCl2 as two factorial experiments. Results showed that Plant Growth-Promoting Microorganisms (PGPMs) influenced mercury absorption and distribution in different plant organs. Aside from biochar, all stimulators increased the plant's Hg concentration. Although EDTA greatly increased mercury accumulation in plants, it reduced biomass. Fungal and bacterial treatments increased total mercury in the plant but decreased its concentration in the leaves. The combination of bacteria and fungi resulted in the highest mercury absorption, while the biochar in combination with PGPMs produced the greatest biomass. Analysis of mercury concentration in seeds indicated that V radiata effectively prevented its contamination in seeds. The results disclosed that microbial combinations of bacteria and fungi could increase the plant's potential to cope with heavy metal pollution. This improvement is due to the different roles of these two organisms, like nitrogen fixation by bacteria and phosphorus absorption by mycorrhiza fungi. Moreover, biochar as a soil amendment and microorganism carrier was noticed. Finally, considering the plant's inherent capacity to stabilize mercury in the roots, phytostabilization with the benefit of combined levels of biochar and microorganisms can be introduced as the best approach.

The effect of biofertilizers on nickel accumulation, nitrogen metabolism and amino acid profile of corn (Zea mays L.) exposed to nickel stress

The issue of heavy metal pollution such as nickel poses a significant environmental concern, exerting detrimental effects on the growth and viability of plant life. Plants have various mechanisms to effectively manage heavy metal stress, including the ability to modify their amino acid type and content. This adaptive response allows plants to mitigate the detrimental effects caused by excessive heavy metal accumulation. The aim of this study was to investigate the effect of biofertilizers on nickel accumulation, nitrogen metabolism and amino acid profile of corn (Zea mays L.) cv. 'PL438' exposed to Ni stress. After disinfecting and soaking in water for 24 h, corn seeds were primed with bacterial biofertilizers (T2: NPK + FZ), fungal biofertilizers (T3: Arbuscular mycorrhizal fungi (AMF) + Trichoderma (T)), or a combination of them (T4: NPK + FZ + AMF + T) and were cultured by the hydroponic method in completely controlled conditions. Then, they were simultaneously exposed to nickel chloride at various rates (0, 75, or 150 µM) at the three-leaf stage. They were harvested two weeks later and were subjected to the measurement of Ni content, nitrate and nitrite content, nitrate reductase activity, and amino acid profile by high-performance liquid chromatography. The results showed that the application of Ni at higher rates increased Ni, nitrate, and nitrite contents and nitrate reductase activity. The study of Ni accumulation and TF revealed that Ni accumulated in the roots to a greater extent than in the shoots and TF was < 1 in all treatments. The shoot amino acid profile showed that the treatment of Ni+2 increased som amino acids such as aspartic acid, asparagine, serine, histidine, and glycine versus the control, whereas T4 Ni+2 increased aspartic acid, glutamic acid, threonine and arginine. The change in amino acids in Ni-treated plants may play a key role in their adaptation to Ni stress. The findings indicate that biofertilizers played a crucial role in mitigating the negative impacts of Ni on corn plants through alterations in amino acid composition and decreased absorption and translocation of Ni.

Changes in Phenolic Profile and Total Phenol and Total Flavonoid Contents of Guadua angustifolia Kunth Plants under Organic and Conventional Fertilization

Agronomic management of a crop, including the application of fertilizers and biological inoculants, affects the phenol and flavonoid contents of plants producing these metabolites. Guadua angustifolia Kunth, a woody bamboo widely distributed in the Americas, produces several biologically active phenolic compounds. The aim of this study was to evaluate the effect of chemical and organic fertilizers together with the application of biological inoculants on the composition of phenolic compounds in G. angustifolia plants at the nursery stage. In 8-month-old plants, differences were observed in plant biomass (20.27 ± 7.68 g) and in the content of total phenols and flavonoids (21.89 ± 9.64 mg gallic acid equivalents/plant and 2.13 ± 0.98 mg quercetin equivalents/plant, respectively) when using the chemical fertilizer diammonium phosphate (DAP). No significant differences were found owing to the effect of the inoculants, although the plants with the application of Stenotrophomonas sp. on plants fertilized with DAP presented higher values of the metabolites (24.12 ± 6.72 mg gallic acid equivalents/plant and 2.39 ± 0.77 mg quercetin equivalents/plant). The chromatographic profile of phenolic metabolites is dominated by one glycosylated flavonoid, the concentration of which was favored by the application of the inoculants Azospirillum brasilense, Pseudomonas fluorescens, and Stenotrophomonas sp. In the case study, the combined use of DAP and bacterial inoculants is recommended for the production of G. angustifolia plant material with a high content of promising biologically active flavonoids or phenolics.

Plant Essential Oils as Biopesticides: Applications, Mechanisms, Innovations, and Constraints

The advent of the "Green Revolution" was a great success in significantly increasing crop productivity. However, it involved high ecological costs in terms of excessive use of synthetic agrochemicals, raising concerns about agricultural sustainability. Indiscriminate use of synthetic pesticides resulted in environmental degradation, the development of pest resistance, and possible dangers to a variety of nontarget species (including plants, animals, and humans). Thus, a sustainable approach necessitates the exploration of viable ecofriendly alternatives. Plant-based biopesticides are attracting considerable attention in this context due to their target specificity, ecofriendliness, biodegradability, and safety for humans and other life forms. Among all the relevant biopesticides, plant essential oils (PEOs) or their active components are being widely explored against weeds, pests, and microorganisms. This review aims to collate the information related to the expansion and advancement in research and technology on the applications of PEOs as biopesticides. An insight into the mechanism of action of PEO-based bioherbicides, bioinsecticides, and biofungicides is also provided. With the aid of bibliometric analysis, it was found that ~75% of the documents on PEOs having biopesticidal potential were published in the last five years, with an annual growth rate of 20.51% and a citation per document of 20.91. Research on the biopesticidal properties of PEOs is receiving adequate attention from European (Italy and Spain), Asian (China, India, Iran, and Saudi Arabia), and American (Argentina, Brazil, and the United States of America) nations. Despite the increasing biopesticidal applications of PEOs and their widespread acceptance by governments, they face many challenges due to their inherent nature (lipophilicity and high volatility), production costs, and manufacturing constraints. To overcome these limitations, the incorporation of emerging innovations like the nanoencapsulation of PEOs, bioinformatics, and RNA-Seq in biopesticide development has been proposed. With these novel technological interventions, PEO-based biopesticides have the potential to be used for sustainable pest management in the future.

Exploring the Plant Growth-Promotion of Four Streptomyces Strains from Rhizosphere Soil to Enhance Cucumber Growth and Yield

The genus Streptomyces is the most abundant and essential microbes in the soil microbial community. Streptomyces are familiar and have great potential to produce a large variety of bioactive compounds. This genus considers an efficient biofertilizer based on its plant growth-promoting activities. Based on their ability to produce a wide varieties of bioactive molecules, the present study aimed to explore the potential plant growth promotion of four Streptomyces strains and their role in enhancing cucumber growth and yield under greenhouse conditions. Streptomyces sp. strain HM2, Streptomyces thinghirensis strain HM3, Streptomyces sp. strain HM8, and Streptomyces tricolor strain HM10 were chosen for the current study. Plant growth-promoting (PGP) features, i.e., indole acetic acid (IAA) production, siderophore excretion, and solubilizing phosphate, were evaluated in vitro. All four strains produced IAA, siderophore, and immobilized inorganic phosphate. Following 4 days of incubation at 30 °C, strains HM2, HM3, HM8, and HM10 produced copious amounts of IAA (18, 22, 62, and 146 µg/mL, respectively) and siderophores (42.59, 40.01, 16.84, 64.14% SU, respectively). At the same time, P solubilization efficacy scored 64.3%, 84.4%, 57.2%, and 81.6% with the same frequency. During in planta evaluation, selected Streptomyces strains combined with rock phosphate were assessed as biofertilizers on the growth and yield of cucumber plants. Under all treatments, positive and significant differences in studied traits were manifested except dry stem matter (SDM), net assimilation rate (NAR), relative growth rate (RGR), and fruit firmness (FF). Treatment T4 (rock phosphate + strain HM3) followed by T5 (rock phosphate + strain HM8) revealed the best results for plant height (PH), number of leaves per plant (NLPP), root length (RL), number of fruits per plant (NFPP), fruit length (FL), fruit diameter (FD), fruit fresh weight per plant (FFWPP), soil P (SP) after 21 DAT, and soil P at the end of the experiment. Notably, T6 (rock phosphate + strain HM10) caused a considerable increase in leaf area (LA). Plant growth-promoting bacteria enhance plant growth and yield through phosphorus solubilizing, improve nutrient availability, produce phytohormones, and support plant growth under abiotic stress. These features are important for sustainable agriculture and reducing environmental pollution with chemical fertilizers and pesticides.

Bio-Chemical Fertilizer Improves the Oil Yield, Fatty Acid Compositions, and Macro-Nutrient Contents in Nigella sativa L

The present study evaluated the effects of biofertilizers on qualitative and quantitative traits of Nigella sativa L. The experiment was conducted based on a randomized complete block design with 10 treatments and three replications. The treatments included control (no fertilization), U (100% chemical fertilizer as urea at 53.3 kg ha−1, Nb (Biofertilizer, Azotobacter vinelandii), Pb (Biofertilizer, Pantoea agglomerans and Pseudomonas putida), Kb (Biofertilizer, Bacillus spp.), NPKb (NPK combined biofertilizers), Nb + 50% U, Pb + 50% U, Kb + 50% U, and NPKb + 50% U. The highest oil percentage was 46.33 percent related to NPK(b) + U50%, and the highest oil yield was 466.43 kg/ha related to NPK(b) + U50%. The highest seed yield (1006.64 kg/ha) was observed in the plants treated with NPK(b) + U50%. The treatment of K(b) + U50% increased myristic acid by 0.35%. The NPK(b) + U50% treatment reduced palmitic, stearic, and linolenic acid by 11.3, 2.01, and 0.31%, respectively. The highest oleic acid (27.85%) and linoleic acid (56.6%) were obtained from the treatment of NPK(b) + U50%, respectively. The plants treated with NPK(b) + U50% showed the highest seed N percentage (%), P content (mg g−1) and K content (mg g−1). In general, NPK(b) + U50% is the best treatment in line with sustainable agriculture.