Soybean Seedlings Research Articles

Diversity and Aggressiveness of Rhizoctonia spp. from Nebraska on Soybean and Cross-Pathogenicity to Corn and Wheat.

Rhizoctonia and Rhizoctonia-like species of fungi that cause disease are known to have varying host ranges and aggressiveness. Accurate identification of these species causing disease is important for soybean disease management that relies upon crop rotation. The anamorphic genus Rhizoctonia contains several diverse species and anastomosis groups (AGs) including some known soybean pathogens, such as Rhizoctonia solani, whereas for others the ability to cause disease on soybean has not been well described. The present study was conducted to identify the predominant species and AG of Rhizoctonia from soybean, corn, and wheat fields that are pathogenic on soybean and characterize cross-pathogenicity to common rotational crops, corn and wheat. We surveyed for Rhizoctonia spp. in Nebraska; isolates were identified to species and AG, and aggressiveness was assessed. A total of 59 R.zeae isolates, 49 R.solani, nine binucleate Rhizoctonia, three R.circinata, and two R.oryzae isolates were collected in 2016 and 2017 from a total of 29 fields in 15 counties. The most abundant R.solani AGs were AG-4, AG-1 IB, AG-2-1, AG-3, and AG-5. R.solani AG-4 and R. zeae were found in all three regions of the state (west, central, and eastern). Some isolates that were most aggressive to soybean seedlings were cross-pathogenic on both wheat and corn. In addition, R. zeae was pathogenic on soybean when evaluated at 25°C, which is warmer than temperatures used previously, and isolates were identified that were aggressive on soybean and cross-pathogenic on both corn and wheat.

Genes encoding for tocopherol pathway and antioxidant enzymes induced by γ-irradiation for improvement of seed quality in soybean (Glycine max)

Aim: The present investigation was aimed to determine the effect of gamma radiation on genes encoding for tocopherol pathway and antioxidant enzymes in two contrasting soybean genotypes seedlings. Methodology: Seeds from two contrasting soybean genotypes (Bragg and DS-74) were exposed to two different doses of gamma irradiation (0.5 and 1.0 kGy), allowed to germinate and RNA was extracted for cDNA synthesis from 3-days-old soybean seedlings. Expression level of tocopherol pathway and antioxidant enzymes genes was carried out using real time PCR. Seed vigour and moisture contents in seeds of both the soybean genotypes were also analysed. Results: Genes encoding tocopherol biosynthesis and redox enzymes showed higher expression upon 0.5 kGy seed irradiation [3.01 and 3.5 fold for SOD and APXandγ-TMT and MPBQ-MT genes (2.87 and 4.21 fold respectively) in Bragg soybean seedlings] as compared at 1.0 kGy dose of gamma irradiation. The moisture content in control and irradiated soybean seed samples ranged from 8.1 to 15.2 % with DS-74 control seeds showing highest moisture content (15.2%) and Bragg seeds (0.5 kGyirradiated) with lowest moisture content (8.1%). 0.5 kGy irradiated Bragg seeds showed highest seed vigour in the form seed germination (72.25 %) and seedling emergence (61.12%). Interpretation: The result showed that 0.5 KGy of γ- irradiation of soybean seeds were more effective in improving the seed quality by enhancing gene expression of tocopherol pathway and antioxidant enzymes. Key words: Antioxidants, Gamma irradiation, Gene expression, Seed vigour, Soybean

Exogenous strigolactones enhance tolerance in soybean seedlings in response to alkaline stress.

The plant hormone strigolactones (SLs) play crucial roles in regulating plant development and adaptations to abiotic stresses. Even though the functional roles of SLs have been identified in response to abiotic stresses, the function, and mechanism of SLs are not fully established under alkaline stress. In this study, we identified that exogenous SL could improve alkaline tolerance of soybean seedlings, especially when treated with 0.5μM SL. The application of SL remarkably reduced the malondialdehyde content, hydrogen peroxide content, and increased the activity of antioxidant enzymes under alkaline stress, suggesting that SL improved the alkaline tolerance by regulating the antioxidant defense capacity. The RNA sequencing data showed 530 special differentially expressed genes under SL treatment and alkaline stress, mainly were associated with antioxidant processes and phenylpropanoid biosynthetic pathway. Some transcription factors were also induced by SL under alkaline stress as confirmed by quantitative real-time PCR (qRT-PCR). Furthermore, SL largely increased the Na content in leaves and decreased Na content in roots under alkaline stress, which suggested that SL might promote the transport of Na from the roots to the leaves of the soybean seedlings. Meanwhile, exogenous SL decreased the content of other elements such as K, Mg, Fe, and Cu in leaves or roots under alkaline stress. Collectively, our results suggested a role of SL in regulating antioxidant defense capacity, specific gene expression, and alterations in ionic contents to alleviate harmful effects of alkaline stress in soybean seedlings.

Field Studies on the Effect of Rye Cover Crop on Soybean Root Disease and Productivity

Cover crops improve soil and water quality in annual cropping systems, but knowledge of their impact on soybean ( Glycine max L.) seedling and root diseases is limited. The effects of winter rye cover crops ( Secale cereale L.) on soybean population, biomass, root morphology, seedling and root diseases, pathogen incidence, canopy reflectance, and yield were assessed over 2 years in Iowa and Missouri, U.S.A. Plots without a rye cover crop were compared with plots with early-kill rye and late-kill rye cover crops, which were terminated 34 to 49 days or 5 to 17 days before soybean planting, respectively. Soybean shoot dry weight, root rot severity, and incidence of Fusarium spp. and Pythium spp. on roots were not influenced by the treatments. Soybean grain yield and plant population were reduced in the presence of rye in 2 site years, increased in 1 site year, and unchanged in the remaining site years. Soybean canopy reflectance was measured at 810 nm, and measurements were first made at 70 to 80 days after planting (DAP). At least five measurements were obtained at 7- to 15-day intervals, ending at 120 to 125 DAP. Measurements at approximately 120 to 125 DAP differed by treatments but were not consistently associated with the presence or absence of a rye cover crop. Our field studies suggest that Iowa and Missouri soybean farmers can use winter rye as a cover crop in soybean fields with low seedling disease pressure without increasing the risk of seedling and root diseases or suppressing yield. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license .

Eficácia do tratamento de sementes com fungicidas no controle do tombamento de plântulas de soja causado por Rhizoctonia solani sob condições casa de vegetação

ABSTRACT The present study was conducted to evaluate the efficacy of fungicide seed treatment in the control of soybean seedling damping-off caused by Rhizoctonia solani under greenhouse conditions. The experiment was carried out in Dourados, Mato Grosso do Sul State, Brazil. Treated and untreated soybean seeds were sown in previously sterilized sand, contained in plastic trays, in equidistant individual wells at 3cm depth. The soybean sowing density was 200 seeds/plastic tray. Inoculation with R. solani was done by homogeneous distribution of the fungal inoculum onto the substrate surface (5.0g/tray). The fungus was grown for 35 days on autoclaved black oat seeds ground to powder with a mill (1mm). Seedling emergence, pre and post-emergence damping-off, injured seedlings and disease index (severity) were evaluated according to McKinney formula. Fungicide seed treatments had a significant effect (P ≤ 0.05) on seedling emergence, pre and post-emergence damping-off, injured seedlings and disease index (severity). The best results were obtained for fludioxonil+metalaxyl-M+thiabendazole and fipronil+pyraclostrobin+thiophanate-methyl, followed by carbendazim+thiram+pencycuron and thiophanate-methyl+fluazinam. The least efficient treatments were carbendazim+thiram, fludioxonil+metalaxyl-M and carboxin+thiram. Pearson correlation analysis indicated that injured seedlings and disease index were positively correlated (R=0.92). This means that the greater the number of injured seedlings, the greater the disease index and the less efficient the fungicide. The fungicides used in the present study did not have any phytotoxic effect on soybean seedlings.

Brassinosteroid Supplementation Alleviates Chromium Toxicity in Soybean (Glycine max L.) via Reducing Its Translocation.

Chromium (Cr) phytotoxicity severely inhibits plant growth and development which makes it a prerequisite to developing techniques that prevent Cr accumulation in food chains. However, little is explored related to the protective role of brassinosteroids (BRs) against Cr-induced stress in soybean plants. Herein, the morpho-physiological, biochemical, and molecular responses of soybean cultivars with/without foliar application of BRs under Cr toxicity were intensely investigated. Our outcomes deliberated that BRs application noticeably reduced Cr-induced phytotoxicity by lowering Cr uptake (37.7/43.63%), accumulation (63.92/81.73%), and translocation (26.23/38.14%) in XD-18/HD-19, plant tissues, respectively; besides, improved seed germination ratio, photosynthetic attributes, plant growth, and biomass, as well as prevented nutrient uptake inhibition under Cr stress, especially in HD-19 cultivar. Furthermore, BRs stimulated antioxidative defense systems, both enzymatic and non-enzymatic, the compartmentalization of ion chelation, diminished extra production of reactive oxygen species (ROS), and electrolyte leakage in response to Cr-induced toxicity, specifically in HD-19. In addition, BRs improved Cr stress tolerance in soybean seedlings by regulating the expression of stress-related genes involved in Cr accumulation, and translocation. Inclusively, by considering the above-mentioned biomarkers, foliar spray of BRs might be considered an effective inhibitor of Cr-induced damages in soybean cultivars, even in Cr polluted soil.

Foliar application of alpha-ketoglutarate plus nitrogen improves drought resistance in soybean (Glycine max L. Merr.)

The aim of the present research was to understand the impacts of foliar nitrogen and α-oxoglutarate on proline accumulation, photosynthesis, and ammonium assimilation of soybean seedlings subjected to drought stress. The data in the present study demonstrated that foliar α-oxoglutarate and nitrogen significantly enhanced leaf glutamine synthetase (GS) activity, glutamate dehydrogenase (GDH) activity, glutamate content, proline content, relative water content (RWC) and photosynthesis of soybean seedlings exposed to drought stress at each stage. Accordingly, the ammonium content was significantly reduced by foliar α-oxoglutarate and nitrogen. These results suggested that a combination of foliar nitrogen plus α-oxoglutarate had an advantage over either foliar nitrogen or foliar α-oxoglutarate in increasing the proline accumulation under drought stress and a combination of foliar nitrogen plus α-oxoglutarate could better mitigate the adverse impacts of drought stress.

Reduction of Pythium Damping-Off in Soybean by Biocontrol Seed Treatment.

Pythium spp. is one of the major groups of pathogens that cause seedling diseases on soybean, leading to both preemergence and postemergence damping-off and root rot. More than 100 species have been identified within this genus, with Pythium irregulare, P. sylvaticum, P. ultimum var ultimum, and P. torulosum being particularly important for soybean production given their aggressiveness, prevalence, and abundance in production fields. This study investigated the antagonistic activity of potential biological control agents (BCAs) native to the U.S. Midwest against Pythium spp. First, invitro screening identified BCAs that inhibit P. ultimum var. ultimum growth. Scanning electron microscopy demonstrated evidence of mycoparasitism of all potential biocontrol isolates against P. ultimum var. ultimum and P. torulosum, with the formation of appressorium-like structures, short hyphal branches around host hyphae, hook-shaped structures, coiling, and parallel growth of the mycoparasite along the host hyphae. Based on these promising results, selected BCAs were tested under field conditions against six different Pythium spp. Trichoderma afroharzianum 26 used alone and a mix of T. hamatum 16 + T. afroharzianum 19 used as seed treatments protected soybean seedlings from Pythium spp. infection, as BCA-treated plots had on average 15 to 20% greater plant stand and vigor than control plots. Our results also indicate that some of these potential BCAs could be added with a fungicide seed treatment with minimum inhibition occurring, depending on the fungicide active ingredient. This research highlights the need to develop tools incorporating biological control as a facet of soybean seedling disease management programs. The harnessing of native BCAs could be integrated with other management strategies to provide efficient control of seedling diseases.

In vitro Bioassay of Allelopathic Activities of Soybean, and Three Isoflavones, Using Protoplast Co-culture Method with Digital Image Analysis

Inhibitory allelopathic activities of dried leaves of potted plants and protoplasts of Glycine max (soybean) cv. Okuhara-wase were studied using two in vitro bioassay methods. Strong inhibition (90%) of growth of recipient lettuce root was obtained with 50 mg soybean leaves using the lettuce seedling growth test (sandwich method), and moderate inhibition (65%) of lettuce protoplast division was obtained with 100 × 103 mL-1 protoplasts of etiolated soybean seedlings using the protoplast co-culture method with digital image analysis (DIA-PP method). Three isoflavones, genistein, genistin (genistein-7-O-glucoside), and daidzin (daidzein-7-O-glucoside) were investigated as putative allelochemicals using the DIA-PP method. The three isoflavones at 100 µM showed early crystal accumulation in lettuce protoplasts and inhibited lettuce protoplast division by 100%. Genistein showed the strongest inhibition. The results were compared and discussed with the previous reports on the invader leguminous plant, Kudzu, and two isoflavones, daidzein and Kudzu-specific puerarin (daidzein-6-C-glucoside), and other allelopathic plants and their putative allelochemicals.

Bio-Synthesized Nanoflowers and Chemically Synthesized Nanowires Zinc-Oxide induced Changes in the Redox and Protein Folding in Soybean Seedlings: a Proteomic Analysis

Bio-Synthesized Nanoflowers and Chemically Synthesized Nanowires Zinc-Oxide induced Changes in the Redox and Protein Folding in Soybean Seedlings: a Proteomic Analysis

Oxathiapiprolin Alone or Mixed with Metalaxyl Seed Treatment for Management of Soybean Seedling Diseases Caused by Species of Phytophthora, Phytopythium, and Pythium.

Species of Phytophthora, Phytopythium, and Pythium affect soybean seed and seedlings each year, primarily through reduced plant populations and yield. Oxathiapiprolin is effective at managing several foliar diseases caused by some oomycetes. The objectives of these studies were to evaluate oxathiapiprolin in a discriminatory dose assay invitro; evaluate oxathiapiprolin as a soybean seed treatment on a moderately susceptible cultivar in 10 environments; compare the impact of seed treatment on plant populations and yields in environments with low and high precipitation; and compare a seed treatment mixture on cultivars with different levels of resistance in four environments. There was no reduction in growth invitro among 13 species of Pythium at 0.1 µg ml-1. Soybean seed treated with the base fungicide plus oxathiapiprolin (12 and 24 µg a.i. seed-1) alone, oxathiapiprolin (12 µg a.i. seed-1) plus mefenoxam (6 µg a.i. seed-1), or oxathiapiprolin (24 µg a.i. seed-1) plus ethaboxam (12.1 µg a.i. seed-1) had greater yields in environments that received ≥50 mm of precipitation within 14 days after planting compared with those that received less. Early plant population and yield were significantly higher for seed treated with oxathiapiprolin (24 µg a.i. seed-1) + metalaxyl (13.2 µg a.i. seed-1) compared with nontreated for six of seven cultivars in at least one of four environments. Oxathiapiprolin combined with another Oomycota fungicide applied to seed has the potential to be used to protect soybean plant establishment and yield in regions prone to poor drainage after high levels of precipitation.

Efficacy of Insecticides Applied to Soybean Seeds for Controlling Lepidoptera Caterpillars

The use of high-quality seeds is essential for the crop to express its full potential. The application of seed treatment constitutes a widely spread operation, every year new products are discovered and used for seed treatment, which can provide a protective effect against pests that attack the seeds, as well as physiological effects to favor the growth and initial development of plants, however, little is known about the influence of insecticides on seed germination and the emergence of soybean seedlings. The experiment was carried out in the Seed Quality Analysis Laboratory and in the experimental field of the Agrarian Sciences Faculty of the National University of Asunción-Paraguay. The objective consisted of evaluating the efficacy of chemical insecticides applied to soybean seeds to control lepidopteran caterpillars during the implantation of the crop, and the effect on the germination of seeds in the laboratory and the emergence in the field. Commercial soybean seeds were used and the treatments were the following (in cc of c.p./100 kg seeds): control (without treatment), thiamethoxam (200), cyantraniliprole + thiamethoxam (200), thiamethoxam + lambda-cyhalothrin (200), imidacloprid (400), imidacloprid + thiodicarb (500) and fipronil (200). The variables evaluated were: germination under laboratory conditions, number of larvae presented at 14, 21 and 28 days after emergence, seedling emergence and efficacy of chemical products in the field. The design used in the field was complete block to the random and in laboratory fully randomized, with seven treatments and 4 replications with a total of 28 experimental units for both trials. The data obtained were compared through the analysis of variance using the statistical software SASM-Agri and those variables that presented significant statistical differences between the means of the treatments were compared using the Scott-Knott test at 5% probability, while efficacy was determined by the Abbot formula. The data show that the chemical insecticides did not affect the germination of seeds in the doses tested. The highest percentages of emergence in the field were obtained with the insecticides thiamethoxam, cyantraniliprole + thiamethoxam, imidacloprid and imidacloprid + thiodicarb. At 28 day after seedling emergence the active ingredients cyantraniliprole + thiamethoxam and imidacloprid + thiodicarb achieved the greatest reduction in the lepidoptera population. Seed treatment with the active ingredients used in this study is an effective practice for the control of Spodoptera frugiperda, Spodoptera cosmioides and Agrotis ipsilon caterpillars during the initial stage of soybean cultivation.

Detection and Imaging of the Plant Pathogen Response By Near Infrared Fluorescent Polyphenol Sensors

Plants use secondary metabolites such as polyphenols for chemical defense against pathogens and herbivores. Despite their importance in plant pathogen interactions and tolerance to diseases, it remains challenging to detect polyphenols in complex plant tissues. Here, we create molecular sensors for plant polyphenol imaging that are based on near-infrared (NIR) fluorescent single wall carbon nanotubes (SWCNTs). We identified polyethylene glycol-phospholipids that render (6,5)-SWCNTs sensitive (Kd = 90 nM) to plant polyphenols (tannins, flavonoids, ...), which red-shift (up to 20 nm) and quench their emission (~1000 nm). These sensors report changes in total polyphenol level after herbivore or pathogen challenge in crop plant systems (Soybean Glycine max) and leaf tissue extracts (Tococa spp). We furthermore demonstrate remote chemical imaging of pathogen-induced polyphenol release from roots of soybean seedlings over the time course of 24h. Additional use of chirality-pure polyphenol sensors gives further access to ratiometric sensing and imaging applications. Overall, this approach allows in situ visualization and understanding of the chemical plant defense in real time and paves the way for plant phenotyping for optimized polyphenol secretion.

Effect of forage aqueous extracts on Glycine max L. Merr., Zea mays L. and Bidens pilosa L.

The aim of the present study was to investigate the potential allelopathic effects of isolated or intercropped aqueous forage extracts on the physiological performance of soybean [Glycine max (L.) Merr.] and corn (Zea mays L.) seeds, as well as their phytotoxicity to the weed species Bidens pilosa L. Aqueous extracts were prepared at a concentration of 5%, and the tests with soy and corn were conducted by wetting the germination papers with different treatments and performing procedures within the standards of the Brazilian Rules of Seed Analysis. Tests with the cover plant extracts on the seeds of B. pilosa used BOD-type repetitions. Fifty weed seeds were placed in a gerbox with filter paper moistened with the different treatments with five repetitions. Distilled water was used as the control in all tests. Extracts of Avena strigosa Schreb and Raphanus sativus L. (radish), cultivated individually and in combination, increased the seed germination percentage (%G) and the length of soybean seedlings. Similarly, extracts of Pennisetum glaucum (L.) R.Br and Crotalaria spectabilis Roth, in individual and combined cultivation, provided gains in corn %G. Furthermore, all tested extracts suppressed germination and decreased the speed of the germination index of the hairy beggarticks when compared to the control, with the radish extract showing the greater reduction effect on the %G of the weed plant B. pilosa. Highlights: The use of Crotalaria as a cover crop has a positive effect on the initial growth of corn. The use of black oat and forage radish intercropped had the potential to increase soybean yield. The use of cover crops contributes to the integrated management of weeds. The choice of cover plant is important for the success of crop rotation.

Morphological and Proteomic Analyses of Soybean Seedling Interaction Mechanism Affected by Fiber Crosslinked with Zinc-Oxide Nanoparticles.

Nanoparticles (NPs) enhance soybean growth; however, their precise mechanism is not clearly understood. To develop a more effective method using NPs for the enhancement of soybean growth, fiber crosslinked with zinc oxide (ZnO) NPs was prepared. The solution of ZnO NPs with 200 nm promoted soybean growth at the concentration of 10 ppm, while fibers crosslinked with ZnO NPs promoted growth at a 1 ppm concentration. Soybeans grown on fiber cross-linked with ZnO NPs had higher Zn content in their roots than those grown in ZnO NPs solution. To study the positive mechanism of fiber crosslinked with ZnO NPs on soybean growth, a proteomic technique was used. Proteins categorized in photosynthesis and secondary metabolism accumulated more in soybeans grown on fiber crosslinked with ZnO NPs than in those grown in ZnO NPs solution. Furthermore, significantly accumulated proteins, which were NADPH oxidoreductase and tubulins, were confirmed using immunoblot analysis. The abundance of NADPH oxidoreductase increased in soybean by ZnO NPs application. These results suggest that fiber crosslinked with ZnO NPs enhances soybean growth through the increase of photosynthesis and secondary metabolism. Additionally, the accumulation of NADPH oxidoreductase might relate to the effect of auxin with fiber crosslinked with ZnO NPs on soybean growth.

Exogenous melatonin enhances soybean (Glycine max (L.) Merr.) seedling tolerance to saline-alkali stress by regulating antioxidant response and DNA damage repair.

Saline-alkali (SA) stress induces excessive reactive oxygen species (ROS) accumulation in plant cells, resulting in oxidative damages of membranes, lipids, proteins, and nucleic acids. Melatonin has antioxidant protection effects in living organisms and thus has received a lot of attention. This study aimed to investigate the effect and regulating mechanism of melatonin treatment on soybean tolerance to SA stress. In this study, cultivars Heihe 49 (HH49, SA-tolerant) and Henong 95 (HN95, SA-sensitive) were pot-cultured in SA soil, then treated with MT (0-300 μM) at V1 stage. SA stress induced ROS accumulation and DNA damage in the seedling roots of both cultivars, causing G1/S arrest in HN95 and G2/M arrest in HH49. Melatonin treatment enhanced the activity of antioxidant enzymes in soybean seedling roots and reduced ROS accumulation. Additionally, melatonin treatment upregulated DNA damage repair genes, thus enhancing the reduction of DNA oxidative damage under SA stress. The effects of melatonin treatment were manifested as decreased RAPD polymorphism, 8-hydroxy-2'-deoxyguanine (8-OH-dG) level, and relative density of apurinic sites (AP-sites). Meanwhile, melatonin treatment partially alleviated the SA-induced G1/S arrest in HN95 and G2/M arrest in HH49, thus enhancing soybean seedling tolerance to SA stress.

Inoculation and coinoculation combined with sulfur treatment boost the physiological quality of seeds and reduce oxidative stress in soybean seedlings

Inoculation and coinoculation combined with sulfur treatment boost the physiological quality of seeds and reduce oxidative stress in soybean seedlings

Improved drought tolerance in soybean by protein elicitor AMEP412 induced ROS accumulation and scavenging

Drought stress is a major limiting factor for soybean production. In this study, protein elicitor AMEP412 was applied on soybean seedlings to promote drought tolerance, and its correlation with alterations in the reactive oxygen species (ROS) in leaves was studied. The plants of soybean cv. Suinong 26 were sprayed with AMEP412 at the V1 stage and then treated with drought stress and rehydration. The alterations in phenotypes, physiological indices, ROS levels and antioxidant system as well as lipid peroxidation were monitored. The results showed that spraying AMEP412 significantly promoted the drought tolerance of soybean seedlings. Soybean seedlings pre-treated with AMEP412 performed better in phenotypes and physiological indexes, like leaf relative water content (RWC), leaf relative conductivity (RC) and osmolytes (free proline, soluble sugar and protein). In addition, the in situ and quantification detection of ROS revealed that AMEP412 pretreatment led to higher accumulation of ROS at the early stage and faster scavenging of ROS at the late stage. Moreover, AMEP412 pretreatment increased the activity of superoxide dismutase (SOD), guaiacol peroxidase (POD), catalase (CAT), ascorbate peroxidase (APX), monodehydroascorbate reductase (MDHAR), dehydroascorbate reductase (DHAR), glutathione reductase (GR), glutathione peroxidase (GPX), and the levels of ascorbate (AsA) and glutathione (GSH), but decreased the level of malondialdehyde (MDA) as compared with only drought treatment. Overall, the results indicated that AMEP412 was effective in alleviating the adverse effects of drought stress, which was partially attributable to the ROS accumulation and scavenging triggered by AMEP412.

Dual RNA Sequencing Analysis of Bacillus amyloliquefaciens and Sclerotinia sclerotiorum During Infection of Soybean Seedlings by S. sclerotiorum Unveils Antagonistic Interactions.

Soybean Sclerotinia stem rot is caused by Sclerotinia sclerotiorum infection, which causes extensive and severe damage to soybean production. Here, we isolated and patented a Bacillus amyloliquefaciens strain, and used it to verify the antagonistic effect of B. amyloliquefaciens on S. sclerotiorum and to explore the possible underlying mechanism. First, we conducted a plate confrontation experiment using the two microbes. Then, inoculation of soybean (Glycine max) seedlings with S. sclerotiorum (Gm-Ss), B. amyloliquefaciens (Gm-Ba), and their combination (Gm-Ba-Ss) was performed, followed by dual RNA sequencing analysis. Plate confrontation and inoculation experiments showed that B. amyloliquefaciens significantly antagonized S. sclerotiorum growth. The average number of fragments per kilobase of transcript per million fragments mapped of S. sclerotiorum transcripts in Gm-Ss and Gm-Ba-Ss inoculation treatments were 117.82 and 50.79, respectively, indicating that B. amyloliquefaciens strongly inhibited gene expression of S. sclerotiorum. In contrast, the average number of fragments per kilobase of transcript per million fragments mapped of B. amyloliquefaciens transcripts in Gm-Ba and Gm-Ba-Ss inoculation treatments were 479.56 and 579.66, respectively, indicating that S. sclerotiorum promoted overall gene expression in B. amyloliquefaciens. For S. sclerotiorum, 507 upregulated and 4,950 downregulated genes were identified among 8,975 genes in the paired comparison Gm-Ba-Ss vs. Gm-Ss. These differentially expressed genes (DEGs) were significantly enriched in the ribosome (ko03010) KEGG pathway. Additionally, for B. amyloliquefaciens, 294 upregulated and 178 downregulated genes were identified among all 3,154 genes in the paired comparison Gm-Ba-Ss vs. Gm-Ba, and these DEGs were mainly and significantly enriched in metabolism-related KEGG pathways, including the citrate cycle (ko00020) and carbon metabolism (ko01200). We concluded that B. amyloliquefaciens inhibits the expression of genes encoding the ribosomal subunit of S. sclerotiorum, resulting in protein synthesis inhibition in S. sclerotiorum, and thus had a strong antagonistic effect on the fungus. This study provides a scientific basis for the biological control of S. sclerotiorum by B. amyloliquefaciens.

Crude Aqueous Root Extracts of Solanum spp. Show Nematotoxic Activity Against Meloidogyne incognita

Brazilian crops are strongly affected by the root-knot nematode Meloidogyne incognita, which compromises food production and causes serious economic losses around the world. Synthetic nematicides are still some of the main control strategies for this pathogen, despite the high risk to human health and the environment. Therefore, sustainable biotechnology represents a viable alternative for nematode control. Plants of the Solanaceae family are present in several biomes and are a source of secondary metabolites of various chemical classes. In this context, the nematotoxic effect of crude aqueous root extracts (CAREs) of three Solanum species was investigated: Solanum americanum, S. subinerme and S. lycocarpum. CARE showed high nematicidal activity (94.6±9.2% mortality, p ≤ 0.001) against second-stage juveniles (J2) of M. incognita, even after heating to 50 °C. These CAREs also inhibited hatching of juveniles (98.4±0.7% of mortality, p ≤ 0.001) in addition to presenting a mean lethal dose of 336 μg ml-1. No toxic activity was observed against non-target organisms, such as fungi (Trichoderma harzianum and Trichoderma asperellum), yeast (Candida maltosa), nitrogen-fixing bacteria (Bradyrhizobium diazoefficiaens, B. japonicum), two strains of Azospirillum brasilense, AbV 5 and AbV 6 and Bacillus [2538 Ba]. Bioassay performed in a greenhouse demonstrated that CAREs of these species were effective in reducing the number of egg masses and galls (> 85%, p ≤ 0.0001), and did not show a phytotoxic effect on soybean seedlings. Our findings indicate that CAREs from plants of the Solanaceae family, especially S. lycocarpum, demonstrated nematotoxic activity on J2 and inhibited the hatching of Meloidogyne incognita eggs, representing an ecologically appropriate tool to control nematode infection in crops worldwide.