Bean Roots Research Articles

Mitigation of vanillic acid‐promoted faba bean Fusarium wilt by faba bean–wheat intercropping

AbstractLong‐term continuous monocropping of faba beans increases the incidence of faba bean wilt, while faba bean–wheat intercropping can effectively control it. This study aimed to understand the underlying mechanism of faba bean–wheat intercropping for the control of Fusarium oxysporum and vanillic acid (VA)‐promoted occurrence of faba bean wilt. The occurrence of faba bean wilt was investigated among the monocropped and intercropped plants of faba beans in a field experiment. The contents and types of phenolic acids were examined in the rhizosphere soil. Monocropped and intercropped faba beans were examined under the dual stress of F. oxysporum and different concentrations of VA (0, 50, 100, 200 mg/L) to understand the alleviating mechanism of faba bean–wheat intercropping. Exogenous addition of high concentrations of VA significantly inhibited the growth and reproduction of F. oxysporum, but under the dual stress of F. oxysporum and different concentrations of VA, it significantly inhibited the defence enzymes of faba bean roots, stems, and leaves, and rhizosphere soil enzymes. Interestingly, faba bean–wheat intercropping alleviated VA stress and thereby the incidence and disease index of faba bean Fusarium wilt by improving plant resistance and soil enzyme activity. The dual stress of F. oxysporum and VA promotes the occurrence of Fusarium wilt by damaging the defence system of the faba bean root system and rhizosphere soil environment. However, faba bean–wheat intercropping effectively alleviates the autotoxicity of VA by improving the physiological and biochemical resistance of faba beans and soil enzyme activities, and thus controls the occurrence of Fusarium wilt.

The Three Sisters of Agriculture: An Active Learning Activity on Symbiotic Nitrogen Fixation

This active learning exercise introduces students to the plant microbiome and the contributions that bacteria make to plant growth and food production. The Three Sisters are an ancient indigenous practice in which three plant crops and the associated microbiome contribute to each other&rsquo;s growth. In this symbiotic relationship, the associated bacteria (<em>Rhizobium leguminosarum</em> biovar <em>phaseoli</em>) inhabit root nodules in bean plants, converting atmospheric nitrogen to ammonia through the process of nitrogen fixation. The plant takes up the ammonia as its nitrogen source, and provides the bacteria with organic carbon. The Lesson contains a pre-class reading, a 50-minute class session, and an after-class reading. In the first round of small group work during the class, students discuss and report back on the symbiosis between the three plants and between the bacteria and the plants, and the contributions to sustainable agriculture. In the second round of discussion and reporting, students discuss nitrogen fixation, emphasizing the <em>nod</em> genes for polypeptides involved in forming the root nodules and the <em>nif</em> genes that encode the nitrogenase enzyme complex that carries out nitrogen fixation. The after class reading provides students with an example of enhancing plant growth by adding nitrogen-fixing bacteria externally to beans. Altogether, this exercise provides students with a real life scenario relevant to sustainable agriculture. <em>Primary Image:</em>&nbsp;Nitrogen fixation in bean root nodules. Nodule formation starts with the secretion of flavonoids from bean roots, leading to the induction of nodulation factors in the bacteria. After root curling and nodule formation, the enzyme nitrogenase catalyzes the reaction from atmospheric nitrogen to plant accessible ammonia.

Consequences of COVID-19 on my experiment of gene overexpression in beans

&lt;p&gt;My name is Salma Meléndez and I am currently a graduate in Agrogenomic Sciences. In March 2020, when COVID-19 was detected in Mexico, I was in my eighth semester of my undergraduate degree. At that time, he had an experiment of overexpression of a gene in bean roots, in order to explore its function during symbiosis with rhizobial bacteria. Unfortunately, the laboratory and the entire campus canceled their face-to-face activities in order to reduce the risk of contagion. An alternative was to take the experimental plants to my house to give the proper care, however, the situation became difficult as I did not have the space or the required conditions at home. On the other hand, other research centers with which we had collaboration agreements also canceled access, such is the case of the Optical Research Center, where we used the confocal microscope to detect subcellular location of proteins. The closure of institutions allowed me to write theoretical parts of my thesis, however, the experimental phase was definitely affected for at least six months. The experiment with the plants was almost completely lost. In the subsequent months I had the opportunity to re-enter my institution; however, under strict conditions and on staggered days, which made certain measurements that require daily continuity difficult. Currently, the laboratory is not as it used to look, full of colleagues sharing results and difficulties, exchanging advice and even certain materials. I think the pandemic has pushed us to do our work more individually and slowly. Consequently, my degree was delayed and transferred from 2020 to 2021. There are still many challenges to overcome, although activities have not been fully restored, science does not stop and we have found a way to face it, slowly but surely.&lt;/p&gt;

Evaluation of biocontrol potential of Achromobacter xylosoxidans strain CTA8689 against common bean root rot

The purpose of this research was to explore the control of common bean root rot disease caused by Fusarium solani by the bacterial strain CTA8689 under in vitro and greenhouse conditions. The strain CTA8689 was isolated from common bean root and identified as Achromobacter xylosoxidans using 16S rDNA sequence, morphological and physiological characteristics. The strain CTA8689 suppressed the mycelial growth of F. solani in dual-culture (58.67%) and culture filtrates (41.87%) methods. The volatile compounds (VOCs) produced by CTA8689 inhibited mycelial growth and conidial germination of F. solani by 42.26% and 59.12%, respectively. Also, this strain produced biofilm, lytic enzymes such as chitinase, protease and pectinase, siderophore, IAA and gibberellin, and it was able to phosphate solubilization. Furthermore, the disease severity of common bean root rot was reduced using soil and seed treatment by 83.89% and 87.60%, respectively, 60 days after inoculation. Additionally, the strain improved the plant growth parameters in common bean under greenhouse conditions. The VOCs produced by the strain CTA8689 were analyzed by Gas chromatography-mass spectroscopy (GC-MS). Out of 23 identified VOCs, 1,3-Dimethylbenzene (21.613%), Benzene, 1,3-bis (1,1-dimethylethyl)- (13.823%%), Ethylbenzene (8.636%), Dodecane, 4,6-dimethyl- (8.145%) and Decane (5.905%), were the major bioactive components. The mode of action of the strain CTA8689 on the F. solani was through the production of antifungal compounds (antibiosis) and lytic enzymes, which suppressed mycelial growth and conidial germination of the pathogen in vitro and greenhouse conditions. Overall, our results showed that A. xylosoxidans strain CTA8689 could be a promising biological control agent (BCAs) for common bean root rot.

Wheat and faba bean intercropping changes phenolic acids from roots to rhizosphere

The changed phenolic acids (PAs) allelochemicals exuded by the roots induced by interspecific interactions is related to intercropping alleviates soil-borne disease. However, the presence of PAs in roots and root exudations and their rhizodeposition under intercropping are still unclear. Hydroponic and soil experiments of wheat, faba bean, and wheat intercropped with faba bean were conducted, and the major compositions and contents of PAs in roots, root exudations, and rhizospheric soil were determined. The results showed that ρ-hydroxybenzoic, vanillic, and syringic acids were the major components of PAs in roots, root exudations, and rhizospheric soil in a wheat and faba bean intercropping system. The compositions and percentages of PAs in roots of faba bean were altered when faba bean intercropped with wheat. The total exudation rate of PAs in root exudations was decreased by 30%–60% under the wheat and faba bean intercropping (W//F) system as compared to mono-cropped faba bean (MF). ρ-hydroxybenzoic acid was identified in the root exudation of both MF and mono-cropped wheat (MW), but not detected in the intercropping on 60 days after transplanting. Vanillic acid was only detected in the root exudation of MF on 30 days after transplanting. The rhizodepostion of vanillic and cumaric acid were decreased at both branching and pod setting stages in W//F as compared to MF. In conclusion, interspecific interaction changed the compositions and contents of PAs in faba bean roots and root exudations. W//F constrained vanillic acid exuded by roots and decreased vanillic and coumaric acid rhizodeposition by faba bean, which provides insight into root-soil interactions in the intercropping systems.

Occurrence of root rot caused by Pythium aphanidermatum on mung bean (Vigna radiata) in China.

In Aug 2019, approximately 10% of mung bean plants at the experimental farm of the Jiangsu Academy of Agricultural Science (32.03 N; 118.88 E) showed symptoms of stunting and wilting. Brown and water-soaked stem lesions were often observed at the base of the diseased plants. In severe cases, the plants collapsed and cumulous aerial mycelia were visible on the basal stem surface (Figure S1 A). To identify the causal agent, a total of 20 tissue fragments (5 mm long) were excised from roots and basal stems of five symptomatic plants. The fragments were surface sterilized in 2% sodium hypochlorite solution then plated on 2.5% potato dextrose agar (PDA) plates containing 10 μg/mL pimaricin, 100 μg/mL ampicillin, 10 μg/mL rifampicin, and 10 μg/mL pentachloronitrobenzene (PARP; Beckerman et al. 2017). After 3-4 days incubation at 25oC in dark, 14 colonies with white and cumulous mycelia grew from the tissue pieces (named as JS19-1 to JS19-14). JS19-1 and JS19-2 were purified by hyphal tipping, then grown on PDA medium for 7 days for morphological observation using a compound microscope (Figure S1 B, C). Width of coenocytic hyphae ranged from 3.7 to 8.9 (avg. 6.1, n=20) μm. Terminal oogonia were globose and with a diameter of 13.8 to 25.8 (avg. 22, n=20) μm. Antheridia were barrel-shaped, and mostly intercalary, sometimes terminal. Most of antheridia were diclinous, with 6.2 to 12.5 (avg. 9.3, n=20) μm in width and 7.6 to 15.3 (avg. 12.8, n=20) μm in length. Oogonia were fertilized with one or two (rare) antheridia. Oospores were aplerotic, 10.1 to 23.5 (avg. 20.4, n=20) μm in diameter. Sporangia had terminal inflated hyphal branches (Figure S1 D, E). The two isolates were preliminary identified as Pythium aphanidermatum. For molecular identification, the sequences of internal transcribed spacer (ITS) rDNA, cytochrome oxidase subunit I (CoxI) (Robideau et al. 2011), and β-tubulin (Kroon et al. 2004) of JS19-1 were detected, and deposited in GenBank (MT949538, MT949539 and MT949540). The ITS and CoxI sequences were identical with P. aphanidermatum CBS28779 ITS (759/759 bp, HQ643439.1) and PYT01 CoxI (640/640 bp, MH760243.1) respectively, the β-tubulin sequence showed 99% (830/840 bp) similarity of P. aphanidermatum P2 (AY564048.1). Thus, JS19-1 was confirmed as P. aphanidermatum. To fulfill Koch's postulates, the pathogenicity of JS19-1 was tested using the procedure of Kiyoshi et al. (2021) with some modifications. Barley grains infested with JS19-1 were as inoculum and thoroughly mixed with potting mixture at a rate of 10% in volume. Six mung bean seeds were sown per pot and then grown in a greenhouse. Potting mixture with no inoculum was used as control. Three pots of replicate plants used for inoculation and control. After 3 weeks, emergence in the inoculated pots was 33% and symptoms of stunting and root rot similar to those in field were observed, while control plants were asymptomatic (FigureS1 F, G). P. aphanidermatum was successfully reisolated from symptomatic plants of both methods. The pathogenicity tests were repeated twice. P. aphanidermatum causes seed rot, pre- and postemergence damping-off, or stem/root rot of a wide range of industrial crops and vegetables (Liu et al, 2018). To our knowledge, this is the first report of P. aphanidermatum causing disease on mung bean in China. Since Phytophthora vignae (Sun et al, 2020) and P. myriotylum (Yan et al, 2021) have been reported causing mung bean root rot, integrated disease management should be adopted to reduce damage.

Soil health indicators for Central Washington orchards.

Soil health assessment can be a critical soil testing tool that includes biological and physical indicators of soil function related to crop and environmental health. Soil health indicator minimum data sets should be regional and management goal specific. The objective of this study was to initiate the steps to develop a soil assessment tool for irrigated orchard soils in Central Washington, United States including defining objectives, gathering baseline data and selecting target indicators. This study measured twenty-one biological, physical and chemical properties of soils in irrigated Central Washington apple orchards including indicators of water availability, root health, fertility, and biological activity. Soil factors were related to fruit yield and quality. Principal components and nonlinear Bayesian modeling were used to explore the relationship between soil health indicators and yield. Soil indicators measurements in Washington state orchards varied widely but generally had lower organic matter, available water capacity, wet aggregate stability and higher percent sand than in other regions. Linear mixed effects models for available water capacity and percent sand showed significant effects on yield, and models for root health ratings and Pratylenchus nematodes had moderate effects. The minimum dataset of soil health indicators for Central Washington orchards should include measurements of water availability (available water capacity, percent sand) and of root health (bean root health rating, Pratylenchus nematodes) in addition to standard fertility indicators to meet stakeholder management goals.

Effects of atrazine and butachlor on growth of mung bean (Vigna radiata), water spinach (Ipomoea aquatica) and soil bacteria

Atrazine and butachlor are herbicides extensively applied to control weeds. In this study, the effects of these compounds on the growth of mung bean, water spinach and soil bacteria were determined. The results showed that all offsets of mung bean and water spinach were killed after amendment with atrazine. However, the effects of butachlor on both plants in the dry season were unapparent, while this compound used at 2.0× (4.0 L/ha) severely reduced the growth of the plants in the rainy season. For example, the length of beanstalks, and weight of beanstalks and roots of mung bean grown in the rainy season at 2.0× butachlor were lower by 36.2% and 44.3% compared to the control, respectively. Moreover, the application of butachlor decreased the yield of mung bean. In addition, both atrazine and butachlor inhibited the growth of soil bacteria even after two months. This study showed that these herbicides are highly toxic to mung bean, water spinach, and soil bacteria.

Faba bean root exudates alter pea root colonization by the oomycete Aphanomyces euteiches at early stages of infection

Aphanomyces euteiches is an oomycete pathogen that causes the pea root rot. We investigated the potential role of early belowground defense in pea (susceptible plant) and faba bean (tolerant plant) at three days after inoculation. Pea and faba bean were inoculated with A. euteiches zoospores. Root colonization was examined. Root exudates from pea and faba bean were harvested and their impact on A. euteiches development were assessed by using in vitro assays. A. euteiches root colonization and the influence of the oomycete inoculation on specialized metabolites patterns and arabinogalactan protein (AGP) concentration of root exudates were also determined. In faba bean root, A. euteiches colonization was very low as compared with that of pea. Whereas infected pea root exudates have a positive chemotaxis index (CI) on zoospores, faba bean exudate CI was negative suggesting a repellent effect. While furanoacetylenic compounds were only detected in faba bean exudates, AGP concentration was specifically increased in pea.This work showed that early in the course of infection, host susceptibility to A. euteiches is involved via a plant-species specific root exudation opening new perspectives in pea root rot disease management.

Root morphology and kinetics of Zn absorption by roots of common bean influenced by Zn status of the root environment

Understanding the kinetics of Zn absorption by roots and its effect on morphology of this organ is relevant for improving crop management, but still poorly studied for common beans. Therefore, an experiment was conducted in a hydroponic system with five initial concentrations of Zn (CZnI): 0.0; 1.0; 4.0; 16.0 and 48.0 µmol L-1. The experiment was installed with plants at V3 stage of development and aliquots of the solution collected over 24 h. The maximum absorption rate (Vmax), Michaelis-Menten constant (Km) and the absorption power (α) increased as a function of CZnI. The minimum concentration of Zn estimated for its absorption (Cmin) was at 0.0028 mg L-1. The influx of Zn (Imax) was higher in higher CZnI, 16,0 µmol L-1. Root length, root volume, root Zn content and Zn absorption efficiency increased with the increase of CZnI. Therefore, the increase of CZnI positively influenced kinetic parameters of root Zn absorption and common bean root morphology, characteristics that favor Zn absorption by roots and improves overall plant nutrition, favoring agronomical biofortification practices for Zn and other nutrients.

Nitrogen fixation and crop productivity enhancements co‐driven by intercrop root exudates and key rhizosphere bacteria

Abstract Crop diversity management is widely used to increase agricultural productivity and sustainability. Recent studies have demonstrated that maize root exudates can drive interspecific facilitation to enhance N2 fixation of bean in intercropping systems. However, the mechanisms of N2 fixation enhancement stimulated by root exudates in the intercropping systems remain unclear. Four experiments were designed to provide a progressively deeper understanding of how root exudates stimulate microbial‐mediated N2 fixation. First, the effects of faba bean/maize intercropping on yields and soil microbial communities were determined in a field experiment. Second, root‐derived interspecific facilitation was evaluated using a root partitioning approach. Third, the key microbial taxa in the faba bean rhizosphere were traced using 13C‐labelled maize root exudates. Fourth, the co‐driven mechanism of maize root exudates and micro‐organisms in the faba bean rhizosphere were explored. Faba bean/maize intercropping with maize residue return increased the yields of faba bean (26%), maize (27%) and broccoli (9.1%) compared to that under monocropping. Nodulin‐like 4 (NODL4), chalcone‐flavanone isomerase (CFI) and early nodulin‐like (ENODL2) gene expression in faba bean roots intercropped with maize increased by 1.5–2.3‐fold compared to that observed under monoculture. More than half of the N2 fixation of faba bean increase under intercropping was due to interactions with micro‐organisms. Nine key bacterial genera in the faba bean rhizosphere were identified by 13C‐DNA‐based stable isotope probing analysis. Among them Agromyces, Arthrobacter, Bacillus, Lysobacter and Paenibacillus directly fix N2, while Gemmatimonas, Heliobacillus, Natronocella and Sorangium increase the N2 fixation capacity of Azotobacter by providing additional carbon sources. These key bacteria triggered by maize root exudates played an important role in the rhizosphere facilitation of intercropping. Synthesis and applications. We demonstrated a novel root–root facilitation of N2 fixation and increased crop yields co‐driven by root exudates and rhizosphere bacteria under faba bean/maize intercropping, and nine key bacteria associated with this process were identified by 13C‐DNA‐based stable isotope probing. We recommend the adoption and optimization of intercropping systems with residue return to reduce the shortcomings of continuous cropping and to increase the sustainability of crop production.

Essential Oil of Foeniculum vulgare Mill. as a Green Fungicide and Defense-Inducing Agent against Fusarium Root Rot Disease in Vicia faba L.

Simple SummaryPlant extracts, including essential oils, are a viable alternative method for controlling plant diseases. This work deals with the exploitation of fennel seed essential oil (FSEO) to inhibit Fusarium solani and control Fusarium root rot disease in Vicai faba. In vitro FSEO inhibited mycelium growth by up to 80% at 400 µL/mL of FSEO. In vivo, the protective effects against Fusarium root rot disease were recorded when FSEO was applied to Vicia faba seeds. The FSEO reduced the disease severity from 98% in plants grown in infested soil with Fusarium solani to 60.1% in plants that previously had their seeds treated with FSEO. GC-MS spectrometry analyses showed that the major chemical components in the essential oil were D-limonene, menthol, estragole and 2-decenal. Applications of the essential oil resulted in increased total phenolic and flavonoid contents in leaves compared with untreated inoculated (control) plants. The defense-related genes, such as defensin and chitinase, were differentially expressed. This study revealed that the essential oil of fennel seed was effective as a control agent against Fusarium root rot in broad beans.Fusarium solani, the causative agent of root rot disease is one of the major constraints of faba bean (Vicia faba L.) yield worldwide. Essential oils have become excellent plant growth stimulators besides their antifungal properties. Foeniculum vulgare Mill. (fennel) is a familiar medicinal plant that has inhibitory effects against phytopathogenic fungi. Herein, different concentrations of fennel seed essential oil (FSEO) (12.5, 25, 50, 100, 200 and 400 μL/mL) were examined against F. solani KHA10 (accession number MW444555) isolated from rotted roots of faba bean in vitro and in vivo. The chemical composition of FSEO, through gas chromatography/mass spectroscopy, revealed 10 major compounds. In vitro, FSEO inhibited F. solani with a minimum inhibitory concentration (MIC) of 25 µL/mL. In vivo, FSEO suppressed Fusarium root rot disease in Vicia faba L. by decreasing the disease severity (61.2%) and disease incidence (50%), and acted as protective agent (32.5%) of Vicia faba L. Improvements in morphological and biochemical parameters were recorded in FSEO-treated faba seeds. Moreover, the expression level of the defense-related genes defensin and chitinase was noticeably enhanced in treated plants. This study suggested using FSEO as a promising antifungal agent against F. solani not only to control root rot disease but also to enhance plant growth and activate plant defense.

Silica nanoparticles as pesticide against insects of different feeding types and their non-target attraction of predators

The agricultural use of silica (SiO2) nanoparticles (NPs) has the potential to control insect pests while the safety and tritrophic effects on plants and beneficial natural enemies remains unknown. Here, we evaluate the effects of silica NPs on insect pests with different feeding niches, natural enemies, and a plant. Silica NPs were applied at different concentrations (75–425 mg/L) on field-cultivated faba bean and soybean for two growing seasons. The faba bean pests, the cowpea aphid Aphis craccivora and the American serpentine leafminer Liriomyza trifolii, and the soybean pest, the cotton leafworm Spodoptera littoralis, were monitored along with their associated predators. Additional laboratory experiments were performed to test the effects of silica NPs on the growth of faba bean seedlings and to determine whether the rove beetle Paederus fuscipes is attracted to cotton leafworm-infested soybean treated with silica NPs. In the field experiments, silica NPs reduced the populations of all three insect pests and their associated predators, including rove beetles, as the concentration of silica NPs increased. In soybean fields, however, the total number of predators initially increased after applying the lowest concentration. An olfactometer-based choice test found that rove beetles were more likely to move towards an herbivore-infested plant treated with silica NPs than to a water-treated control, suggesting that silica NPs enhance the attraction of natural enemies via herbivore-induced plant volatiles. In the laboratory, while silica NPs inhibited the development of faba bean roots at 400 mg/L, they did not affect germination percentage, germination time, shoot length, or vigor index compared to the control.

Antagonistic Activity of Indigenous Rhizobacteria through Biosynthesis of Indole-3-Acetic Acid (IAA), Hydrogen Cyanide (HCN), and Siderophores

This study aimed to isolate indigenous Antagonistic Bacteria (AB) against common soil-borne phytopathogens, including Rhizoctonia solani, Phythium sp., Fusarium oxysporum. Biosynthesis of Indole-3-Acetic Acid (IAA), generation of Hydrogen Cyanide (HCN), and siderophores production were assessed for their involvement in the antagonistic activities. Rhizospheric soil of bean roots, sunflowers, wheat, rice, and humic and semi flooded soils were used to isolate twenty-one bacterial strains for phytopathogenic antagonism. It was found that nine isolates have potential antagonistic activity against three common soilborne pathogens. Antifungal productivity for IAA, HCN, and siderophores was screened on the isolates while nine ABs were identified. To choose statistically significant isolate for the formulation, the principal component analysis was performed with five variables (IAA production, siderophores production index, antagonistic activities against three phytopathogens). Among the nine isolates, the isolate Pseudomonas alicaligenes shew a positive correlation with all variables. In particular, the strain demonstrated to be an antagonistic strain against the fungal pathogens and a strong producer of siderophores, HCN and IAA, We prepared the biocontrol agents with rice flour, glutinous rice flour, Monosodium Glutamate and Chitosan that were found to maintain the up to three months for convenience of field applications.

Roots of Crops from the Window of an Forage Expert

Less known infos like the effect of wounding faba bean roots by high temperature, how maize roots climb up slopes, effect of cold on Medicago spp., effect of drought on soybeans, effect of active microbe species diversity in rhizosphere-plant interface on complex interactions on roots, allelochemicals, axial water flow, gravitropism, fine and coarse roots, salt-responsive mechanisms, transport in root cells, phototropism, hormones, nutrient acquasition, hydrotropism and many other important physiologic processes attracting a forage crops academician’s attention and interest were extracted from international studies and reviewed this article.

An NADPH oxidase regulates carbon metabolism and the cell cycle during root nodule symbiosis in common bean (Phaseolus vulgaris)

BackgroundRhizobium–legume symbiosis is a specific, coordinated interaction that results in the formation of a root nodule, where biological nitrogen fixation occurs. NADPH oxidases, or Respiratory Burst Oxidase Homologs (RBOHs) in plants, are enzymes that generate superoxide (O2•−). Superoxide produces other reactive oxygen species (ROS); these ROS regulate different stages of mutualistic interactions. For example, changes in ROS levels are thought to induce ROS scavenging, cell wall remodeling, and changes in phytohormone homeostasis during symbiotic interactions. In common bean (Phaseolus vulgaris), PvRbohB plays a key role in the early stages of nodulation.ResultsIn this study, to explore the role of PvRbohB in root nodule symbiosis, we analyzed transcriptomic data from the roots of common bean under control conditions (transgenic roots without construction) and roots with downregulated expression of PvRbohB (by RNA interference) non-inoculated and inoculated with R. tropici. Our results suggest that ROS produced by PvRBOHB play a central role in infection thread formation and nodule organogenesis through crosstalk with flavonoids, carbon metabolism, cell cycle regulation, and the plant hormones auxin and cytokinin during the early stages of this process.ConclusionsOur findings provide important insight into the multiple roles of ROS in regulating rhizobia–legume symbiosis.

Coupling effects of phosphorus fertilization source and rate on growth and ion accumulation of common bean under salinity stress.

Many agricultural regions in arid and semiarid climate zone need to deal with increased soil salinity. Legumes are classified as salt-sensitive crops. A field experiment was performed to examine the application of phosphorus (P) fertilizer source and rate on growth, chlorophylls and carotenoid content, DNA and RNA content and ion accumulation in common bean (Phaseolus vulgaris L.) cultivated under salinity stress. An experimental design was split-plot with three replicates. The main plots included two P sources, namely single superphosphate (SP) and urea phosphate (UP). The sub-plots covered four P rates, i.e., 0.0, 17.5, 35.0, and 52.5 kg P ha–1. All applied P fertilization rates, in both forms, increased plant height, leaf area, dry weight of shoots and roots per plant, and total dry weight (TDW) in t ha−1. The highest accumulation of N, P, K+, Mg2+, Mn2+, Zn2+, and Cu2+ was determined in the shoot and root of common bean, while 35 kg of P per ha−1 was used compared to the other levels of P fertilizer. The highest P rate (52.5 kg ha−1) resulted in a significant reduction in Na+ in shoot and root of common bean. The response curve of TDW (t ha–1) to different rates of P (kg ha–1) proved that the quadratic model fit better than the linear model for both P sources. Under SP, the expected TDW was 1.675 t ha–1 if P was applied at 51.5 kg ha–1, while under UP, the maximum expected TDW was 1.875 t ha–1 if P was supplied at 42.5 kg ha–1. In conclusion, the 35.0 kg P ha–1 could be considered the best effective P level imposed. The application of P fertilizer as urea phosphate is generally more effective than single superphosphate in enhancing plant growth and alleviating common bean plants against salinity stress.

Abscisic acid implicated in differential plant responses of Phaseolus vulgaris during endophytic colonization by Metarhizium and pathogenic colonization by Fusarium

Metarhizium robertsii is an insect pathogen as well as an endophyte, and can antagonize the phytopathogen, Fusarium solani during bean colonization. However, plant immune responses to endophytic colonization by Metarhizium are largely unknown. We applied comprehensive plant hormone analysis, transcriptional expression and stomatal size analysis in order to examine plant immune responses to colonization by Metarhizium and/or Fusarium. The total amount of abscisic acid (ABA) and ABA metabolites decreased significantly in bean leaves by plant roots colonized by M. robertsii and increased significantly with F. solani compared to the un-inoculated control bean plant. Concomitantly, in comparison to the un-inoculated bean, root colonization by Metarhizium resulted in increased stomatal size in leaves and reduced stomatal size with Fusarium. Meanwhile, expression of plant immunity genes was repressed by Metarhizium and, alternately, triggered by Fusarium compared to the un-inoculated plant. Furthermore, exogenous application of ABA resulted in reduction of bean root colonization by Metarhizium but increased colonization by Fusarium compared to the control without ABA application. Our study suggested that ABA plays a central role in differential responses to endophytic colonization by Metarhizium and pathogenic colonization by Fusarium and, we also observed concomitant differences in stomatal size and expression of plant immunity genes.

Effect of Cadmium Chloride and Cadmium Nitrate on Growth and Mineral Nutrient Content in the Root of Fava Bean (Vicia faba L.).

The present study aimed to analyze the differences in the tolerance of fava bean (Vicia faba cv. Aštar) roots to cadmium in nitrate—Cd(NO3)2—and chloride—CdCl2—solutions. The physiological and biochemical parameters were assessed. The tested doses of Cd (50, 100, 150 and 300 mg/L) did not influence the germination of seeds. However, considerable growth inhibition and dehydration were observed after 96 h incubation. The thickness of roots and rupture of cell membranes increased along with the increasing concentration of the metal in the solution. At a Cd dose of 300 mg/L, irrespective of the solution used, increased nitrogen concentration and no change in sodium content were observed. The content of magnesium increased due to the dose of 100 mg/L (cadmium nitrate) and the content of calcium increased due to the dose of 300 mg/L (in either nitrate or chloride). The correlation analyses pointed to a possible effect of nitrates in the applied solutions on the accumulation of Cd and some minerals in the roots of the given variety of fava bean. This may be important for both research and agricultural practice. The identification of crops with high tolerance to cadmium, as well as knowledge about the mechanisms of ion interactions at the soil solution–plant level, is important in terms of such crops’ use in the process of the remediation of cadmium-contaminated soils coupled with food production.

24-epibrassinolide improves differential cadmium tolerance of mung bean roots, stems, and leaves via amending antioxidative systems similar to that of abscisic acid.

Cadmium (Cd) pollution has attracted global concern. In the present study, the biochemical mechanisms underlying the amelioration of 24-epibrassinolide (eBL) and abscisic acid (ABA) on Cd tolerance of roots, stems, and leaves in mung bean seedlings were comparatively analyzed. Foliar application of eBL markedly ameliorated the growth of mung bean seedling exposed to 100 μM Cd. eBL alone had no significant effects on the activities of antioxidative enzymes and the contents of glutathione (GSH) and polyphenols in the three organs whereas significantly increased the root, stem, and leaf proline contents on average by 54.9%, 39.9%, and 94.4%, respectively, and leaf malondialdehyde (MDA) content on average by 69.0% compared with the controls. When the plants were exposed to Cd, eBL significantly reversed the Cd-increased root ascorbate peroxidase (APX) and superoxide dismutase (SOD) activities, root polyphenol, proline, and GSH levels, leaf chlorophyll contents, and MDA levels in the three organs. eBL significantly restored the Cd-decreased leaf catalase (CAT) activity and leaf polyphenol levels. These results indicated that eBL played roles in maintaining cellular redox homeostasis and evidently alleviated Cd-caused membrane lipid peroxidation via controlling the activity of antioxidative systems. eBL mediated the differential responses of cellular biochemical processes in the three organs to Cd exposure. Furthermore, a comparative analysis revealed that, under Cd stress, the effects of eBL on the biochemical processes were very similar to those of ABA, suggesting that ABA and eBL improve plant Cd tolerance via some common downstream pathways.