Maize/Soybean Relay Strip Intercropping Reduces the Occurrence of Fusarium Root Rot and Changes the Diversity of the Pathogenic Fusarium Species

Characterization of Fusarium solani Associated with Tobacco (Nicotiana tabacum) Root Rot in Henan, China

The aim of this study was to characterize the Fusarium solani species complex (FSSC) population obtained from tobacco roots with root rot symptoms by morphological characteristics, molecular tests, and assessment of pathogenicity. Cultures isolated from roots were white to cream with sparse mycelium on potato dextrose agar, with colony growth of 21.5 ± 0.5 to 29.5 ± 0.5 mm after 3 days. Sporodochia were cream on carnation leaf agar (CLA) and Spezieller Nährstoffarmer agar (SNA), and macroconidia formed in sporodochia were 3 to 6 septate and straight to slightly curved, with wide central cells, a slightly short blunt apical cell, and a straight to almost cylindrical basal cell with a distinct foot shape, ranging in size from 20.92 to 64.37 × 3.91 to 6.57 μm. Microconidia formed on CLA were reniform and fusiform, with 0 or 1 to occasionally 2 septa, that formed on long monophialidic conidiogenous cells, with a size range of 5.99 to 32.32 × 1.76 to 5.84 μm. Globose to oval chlamydospores were smooth- to rough-walled, 6.5 to 13.3 ± 0.37 μm in diameter, and terminal or intercalary and occurred singly, in pairs, or occasionally in short chains on SNA. Molecular tests consisted of sequencing and phylogenetic analysis of the translation elongation factor-1 alpha (EF-1α), RNA polymerase II largest subunit, and second largest subunit regions. All the obtained sequences revealed 98.14 to 100% identity to F. solani in both Fusarium ID and Fusarium MLST databases. Phylogenetic trees of the EF-1α gene and concatenated three-locus data showed that isolates from tobacco in Henan grouped in the proposed group 5, which is nested within FSSC clade 3 (FSSC 5). Twenty-seven of the 28 isolates caused root rot in artificially inoculated tobacco seedlings, with a disease severity index ranging from 15.00 ± 1.67 to 91.11 ± 2.22. Cross-pathogenicity tests showed that three representative isolates were virulent to six species of Solanaceae and two species of Poaceae, with disease severity indexes ranging from 6.12 ± 0.56 to 84.44 ± 0.00, indicating that these isolates have a wide host range. The results may inform the control of tobacco root rot through improved crop rotations.

Antifungal Properties of Streptomyces bacillaris S8 for Biological Control Applications

Soybean (Glycine max), a crucial global crop, experiences yearly yield reduction due to diseases such as anthracnose (Colletotrichum truncatum) and root rot (Fusarium spp.). The use of fungicides, which have traditionally been employed to control these phytopathogens, is now facing challenges due to the emergence of fungicide-resistant strains. Streptomyces bacillaris S8 strain S8 is previously known to produce valinomycin t through a nonribosomal peptide synthetase (NRPS) pathway. The objective of this study was to evaluate the antifungal activity of S. bacillaris S8 against C. truncatum and Fusarium sp., assessing its efficacy against soybean pathogens. The results indicate that strain S8 effectively controlled both above-ground and underground soybean diseases, using the NRPS and NRPS-related compound, suggesting its potential as a biological control in plant-microbe interactions. These findings underscore the pivotal role of the stain S8 in fostering healthy soybean microbial communities and emphasize the significance of microbiota structure studies in unveiling potent biocontrol agents.

Maize/soybean intercropping increases nutrient uptake, crop yield and modifies soil physio-chemical characteristics and enzymatic activities in the subtropical humid region based in Southwest China

Intercropping, a widely adopted agricultural practice worldwide, aims to increase crop yield, enhance plant nutrient uptake, and optimize the utilization of natural resources, contributing to sustainable farming practices on a global scale. However, the underlying changes in soil physio-chemical characteristics and enzymatic activities, which contribute to crop yield and nutrient uptake in the intercropping systems are largely unknown. Consequently, a two-year (2021-2022) field experiment was conducted on the maize/soybean intercropping practices with/without nitrogen (N) fertilization (i.e., N0; 0 N kg ha-1 and N1; 225 N kg ha-1 for maize and 100 N kg ha-1 for soybean ) to know whether such cropping system can improve the nutrients uptake and crop yields, soil physio-chemical characteristics, and soil enzymes, which ultimately results in enhanced crop yield. The results revealed that maize intercropping treatments (i.e., N0MI and N1MI) had higher crop yield, biomass dry matter, and 1000-grain weight of maize than mono-cropping treatments (i.e., N0MM, and N1MM). Nonetheless, these parameters were optimized in N1MI treatments in both years. For instance, N1MI produced the maximum grain yield (10,105 and 11,705 kg ha-1), biomass dry matter (13,893 and 14,093 kg ha-1), and 1000-grain weight (420 and 449 g) of maize in the year 2021 and 2022, respectively. Conversely, soybean intercropping treatments (i.e., N0SI and N1SI) reduced such yield parameters for soybean. Also, the land equivalent ratio (LER) and land equivalent ratio for N fertilization (LERN) values were always greater than 1, showing the intercropping system's benefits in terms of yield and improved resource usage. Moreover, maize intercropping treatments (i.e., N0MI and N1MI) and soybean intercropping treatments (i.e., N0SI and N1SI) significantly (p < 0.05) enhanced the nutrient uptake (i.e., N, P, K, Ca, Fe, and Zn) of maize and soybean, however, these nutrients uptakes were more prominent in N1MI and N1SI treatments of maize and soybean, respectively in both years (2021 and 2022) compared with their mono-cropping treatments. Similarly, maize-soybean intercropping treatments (i.e., N0MSI and N1MSI) significantly (p < 0.05) improved the soil-based N, P, K, NH4, NO3, and soil organic matter, but, reduced the soil pH. Such maize-soybean intercropping treatments also improved the soil enzymatic activities such as protease (PT), sucrose (SC), acid phosphatase (AP), urease (UE), and catalase (CT) activities. This indicates that maize-soybean intercropping could potentially contribute to higher and better crop yield, enhanced plant nutrient uptake, improved soil nutrient pool, physio-chemical characteristics, and related soil enzymatic activities. Thus, preferring intercropping to mono-cropping could be a preferable choice for ecologically viable agricultural development.

The Host Range of Fusarium proliferatum in Western Canada

Fusarium proliferatum is associated with the root rot of many plant species, but knowledge of its impact on western Canadian field crops is limited. This study assessed the host range of this fungus and its effect on plant emergence, plant height, and shoot and root dry weights in repeated greenhouse experiments with wheat, barley, faba beans, peas, lentils, canola, lupine, and soybeans. Infection was confirmed via PCR, and principal component analysis determined the utility of different parameters in assessing host responses. All crops were at least partly susceptible, developing mild to severe disease at the seedling and adult stages, and showing significant reductions in growth. In general, the barley and wheat demonstrated higher tolerances to infection, followed by the faba bean and the pea. The soybean, canola, lupine, and lentil were most susceptible. The canola and the soybean were particularly vulnerable to F. proliferatum at the pre-emergence stage, while infection greatly reduced the lentil's biomass. Reductions in the barley's emergence and other growth parameters, however, occurred only under a high inoculum concentration. Variability in root rot severity among cultivars of the same crop indicated some diversity in host reactions within species. Nonetheless, the absence of fully-resistant crops may pose challenges in managing F. proliferatum in western Canadian cropping systems.

A new Schizophyllum commune strain as a potential biocontrol agent against blueberry root rot

In recent years, blueberry root rot has been caused mainly by Fusarium commune, and there is an urgent need for a green and efficient method to control this disease. To date, research on Schizophyllum commune has focused on antioxidant mechanisms, reactive dye degradation, etc., but the mechanism underlying the inhibition of pathogenic microorganisms is still unclear. Here, the control effects of S. commune on F. commune and blueberry root rot were studied using adversarial culture, tissue culture, and greenhouse pot experiments. The results showed that S. commune can dissolve insoluble phosphorus and secrete various extracellular hydrolases. The results of hyphal confrontation and fermentation broth antagonism experiments showed that S. commune had a significant inhibitory effect on F. commune, with inhibition rates of 70.30% and 22.86%, respectively. Microscopy results showed distortion of F. commune hyphae, indicating that S. commune is strongly parasitic. S. commune had a significant growth-promoting effect on blueberry tissue-cultured seedlings. After inoculation with S. commune, inoculation with the pathogenic fungus, or inoculation at a later time, the strain significantly reduced the root rot disease index in the potted blueberry seedlings, with relative control effects of 79.14% and 62.57%, respectively. In addition, S. commune G18 significantly increased the antioxidant enzyme contents in the aboveground and underground parts of potted blueberry seedlings. We can conclude that S. commune is a potential biocontrol agent that can be used to effectively control blueberry root rot caused by F. commune in the field.

Unravelling Species Diversity and Pathogenicity of Fusarium spp. Associated with Soybean Leaf and Root in Heilongjiang Province, China

Soybean (Glycine max L.) holds significant global importance and is extensively cultivated in Heilongjiang Province, China. Soybean can be infected by Fusarium species, causing root rot, seed decay, stem rot, and leaf blight. In 2021 to 2022, a field survey of soybean diseases was carried out in 11 regions of Heilongjiang Province, and 186 soybean leaves with leaf blight symptoms and 123 soybean roots with root rot symptoms were collected. Unexpectedly, a considerable number of Fusarium isolates were obtained not only from root samples but also from leaf samples. A total of 584 Fusarium isolates (416 from leaves and 168 from roots) were obtained and identified as 18 Fusarium species based on morphological features and multilocus phylogenetic analyses with tef1 and rpb2 sequences. Fusarium graminearum and Fusarium sp. 1 in FOSC were the dominant species within soybean leaf and root samples, respectively. Pathogenicity tests were conducted for all Fusarium isolates on both soybean leaves and roots. Results showed that F. graminearum, F. ipomoeae, F. citri, F. compactum, F. flagelliforme, F. acuminatum, and F. sporotrichioides were pathogenic to both soybean leaves and roots. F. solani, F. avenaceum, F. pentaseptatum, F. serpentinum, F. annulatum, and Fusarium sp. 1 in FOSC were pathogenic to soybean roots, not to leaves. To our knowledge, this is the first study to thoroughly investigate soybean-associated Fusarium populations in leaves and roots in Heilongjiang Province.

Characterization of Fusarium species causing soybean root rot in Heilongjiang, China, and mechanism underlying the differences in sensitivity to DMI fungicides

Soybean root rot is a worldwide soil-borne disease threatening soybean production, causing large losses in soybean yield and quality. Fusarium species are the most detrimental pathogens of soybean root rot worldwide, causing large production losses. Fusarium root rot has been frequently reported in Heilongjiang Province of China, but the predominant Fusarium species and the sensitivity of these pathogens to different fungicides remain unclear. In this study, diseased soybean roots were collected from 14 regions of Heilongjiang province in 2021 and 2022. A total of 144 isolates of Fusarium spp. were isolated and identified as seven distinct species: F. scirpi, F. oxysporum, F. graminearum, F. clavum, F. acuminatum, F. avenaceum, and F. sporotrichioide. F. scirpi and F. oxysporum had high separation frequency and strong pathogenicity. The sensitivity of Fusarium spp. to five different fungicides was determined. Mefentrifluconazole and fludioxonil showed good inhibitory effects, and the sensitivity to pydiflumetofen and phenamacril varied between Fusarium species. In particular, the activity of DMI fungicide prothioconazole was lower than that of mefentrifluconazole. Molecular docking showed that mefentrifluconazole mainly bound to CYP51C, but prothioconazole mainly bound to CYP51B. Furthermore, the sensitivity to prothioconazole only significantly decreased in ΔFgCYP51B mutant, and the sensitivity to mefentrifluconazole changed in ΔFgCYP51C and ΔFgCYP51A mutants. The results demonstrated that the predominant Fusarium species causing soybean root rot in Heilongjiang province were F. scirpi and F. oxysporum and DMI fungicides had differences in binding cavity due to the diversity of CYP51 proteins in Fusarium.

Maize/peanut rotation intercropping improves ecosystem carbon budget and economic benefits in the dry farming regions of China

Monoculture is widely practiced to increase crop productivity, but long-term adaptation has drawbacks as it increases the depletion of soil nutrients and reduces soil quality, especially in dryland areas. Conversion from traditional maize monoculture to intercropping improves sustainable production. However, maize/peanut intercropping, especially rotation of planting strips impacts of maize/peanut intercropping in dryland on carbon (C) budgets and economic benefits remain unclear. In this study, a 5-year field experiment was conducted to evaluate the influence of maize/peanut intercropping with rotation of planting strips on soil health, indirect CO2-eq greenhouse gas emissions, and ecosystem C inputs. Four intercropping treatments viz. maize monoculture, peanut monoculture, maize/peanut intercropping, and maize/peanut rotation-intercropping were tested from 2018 to 2022. Maize/peanut rotation intercropping significantly improved the land equivalent ratio followed by intercropping and monoculture. Rotation-intercropping also improved economic benefits over intercropping and monoculture which were mainly associated with increased peanut yield where the border rows contributed the maximum, followed by the middle rows. Moreover, rotation-intercropping significantly increased the soil organic C and nitrogen (N) content. Rotation-intercropping decreased indirect CO2-eq greenhouse gas emissions and ecosystem C inputs by 3.11% and 18.04%, whereas increased ecosystem C outputs and net ecosystem C budget by 10.38% and 29.14%, respectively, over the average of monoculture. On average for intercropping and monoculture, rotation-intercropping increased ecosystem C emission efficiency for economic benefits by 51.94% and 227.27% in 2021 and 2022, respectively, showing the highest C utilization efficiency than other treatments. In the long run, maize/peanut rotation-intercropping can be practiced in dryland agriculture to achieve sustainable agriculture goals.

Synergistic benefits of Funneliformis mosseae and Bacillus paramycoides: Enhancing soil health and soybean tolerance to root rot disease

To explore the response of soil metabolite composition to soybean disease, the effect of the combined inoculation of arbuscular mycorrhizal fungi (AMF) and plant growth-promoting bacteria on soybean root rot caused by Fusarium oxysporum was studied. A factorial completely randomized design with three factors (AMF, Bacillus. paramycoides, and rot disease stress) was conducted, and eight treatments, including normal groups and stress groups, were performed using pot experiments. GC‒MS and enzymatic assays were used to evaluate the soil factors and soybean growth indicators. The results showed that there were significant differences in the composition of metabolites among the different treatment groups, and 23 metabolites were significantly related to soybean biomass. The combined inoculation of Funneliformis mosseae and Bacillus paramycoides resulted in a significant reduction in harmful soil metabolites associated with root rot disease, such as ethylbenzene and styrene. This reduction in metabolites contributed to improving soil health, as evidenced by enhanced soybean defence enzyme activities and microbial activity, and β-1,3-glucanase, chitinase and phenylalanine ammonia-lyase activities were improved to alleviate plant rhizosphere stress. Furthermore, soybean plants inoculated with the synergistic treatments exhibited reduced root rot disease severity and improved growth indicators compared to control plants. Plant height, root dry weight (RDW), and shoot and root fresh weight (SRFW) were improved by 4.18-53.79%, and the AM fungal colonization rate was also improved under stress. The synergistic application of Funneliformis mosseae and Bacillus paramycoides can effectively enhance soil health by inhibiting the production of harmful soil metabolites and improving soybean tolerance to root rot disease. This approach holds promise for the sustainable management of soil-borne diseases in soybean cultivation.

Quantification of the Cumulative Shading Capacity in a Maize-Soybean Intercropping System Using an Unmanned Aerial Vehicle

In intercropping systems, higher crops block direct radiation, resulting in inevitable shading on the lower crops. Cumulative shading capacity (CSC), defined as the amount of direct radiation shaded by higher crops during a growth period, affects the light interception and radiation use efficiency of crops. Previous studies investigated the light interception and distribution of intercropping. However, how to directly quantify the CSC and its inter-row heterogeneity is still unclear. Considering the canopy height differences (Hms, obtained using an unmanned aerial vehicle) and solar position, we developed a shading capacity model (SCM) to quantify the shading on soybean in maize-soybean intercropping systems. Our results indicated that the southernmost row of soybean had the highest shading proportion, with variations observed among treatments composed of strip configurations and plant densities (ranging from 52.44% to 57.44%). The maximum overall CSC in our treatments reached 123.77 MJ m-2. There was a quantitative relationship between CSC and the soybean canopy height increment (y = 3.61 × 10-2×ln(x)+6.80 × 10-1, P < 0.001). Assuming that the growth status of maize and soybean was consistent under different planting directions and latitudes, we evaluated the effects of factors (i.e., canopy height difference, latitude, and planting direction) on shading to provide insights for optimizing intercropping planting patterns. The simulation showed that increasing canopy height differences and latitude led to increased shading, and the planting direction with the least shading was about 90° to 120° at the experimental site. The newly proposed SCM offers a quantitative approach for better understanding shading in intercropping systems.

Evaluating the influence of straw mulching and intercropping on nitrogen uptake, crop growth, and yield performance in maize and soybean

Introduction

Intercropping and straw mulching are sustainable agricultural practices that can positively affect crop growth and development, especially together.

Methods

A split-plot experimental design was used to investigate the effects of intercropping and straw mulching on crop growth, crop yield, nitrogen uptake, and photosynthetic characteristics. The main plot focused on three planting patterns: soybean monoculture (S), maize monoculture (M), and maize/soybean intercropping (I). The subplot structure consisted of four levels of straw mulching (0, 4.8, 7.2, 9.6 t ha-1).

Results

Interaction and variance analyses showed that straw mulching, intercropping, and their interaction had significant effects on plant height, stem diameter, leaf area index, chlorophyll content, nitrogen uptake, photosynthetic characteristics, and crop yield. Based on two-year averages for maize and soybean, the net photosynthetic rate (Pn) was up to 51.6% higher, stomatal conductance (Sc) was up to 44.0% higher, transpiration rate (Tr) was up to 46.6% higher, and intercellular carbon dioxide concentration (Ci) was up to 25.7% lower relative to no mulching. The maximum increases of Pn, Sc, and Tr of intercropped maize were 15.48%, 17.28%, and 23.94%, respectively, and the maximum Ci was 17.75% lower than that of monoculture maize. The maximum increase of Pn, Sc, and Tr of monoculture soybean was 24.58%, 16.90%, and 17.91%, respectively, and the maximum Ci was 13.85% lower than that of intercropped soybean. The nitrogen uptake of maize and soybean in the mulching treatment was 24.3% higher than that in the non-mulching treatment; the nitrogen uptake of intercropped maize was 34.2% higher than that of monoculture maize, and the nitrogen uptake of monoculture soybean was 15.0% higher than that of intercropped soybean. The yield of maize and soybean in the mulching treatment was 66.6% higher than that in the non-mulching treatment, the maize yield under intercropping was 15.4% higher than that under monoculture, and the yield of monoculture soybean was 9.03% higher than that of intercropped soybean.

Discussion

The growth index and photosynthesis of crops are important parts of yield formation. The results of this study confirmed that straw mulching, intercropping, and their interaction can ultimately increase crop yield by improving crop growth, nitrogen uptake, and photosynthesis. This result can be used as the theoretical basis for the combined application of these measures in agriculture.

Identification and Pathogenicity of Fusarium Isolated from Soybean in Poland

Fungi belonging to the Fusarium genus are commonly isolated from soybean plants and seeds but not all of them are pathogenic. The aim of this study was to compare the pathogenicity among different Fusarium isolates obtained from soybean plants with disease symptoms originating from an experimental field located in the southeast of Poland. Nineteen fungal isolates were selected for the pathogenicity assay, including eight isolates of F. oxysporum, six isolates of F. graminearum, four isolates of F. culmorum and one isolate of F. redolens. Species identification of these isolates was carried out using microscopic methods and sequencing of two genes: translation elongation factor 1-alpha (TEF1) and RNA polymerase second largest subunit (RPB2). To our knowledge, this is the first report of F. redolens being isolated from soybean in Europe. The pathogenicity test was set up by fungal inoculation of healthy soybean seeds of three cultivars: Abelina, Atlanta and Mavka. Symptoms were assessed seven days after inoculation. Disease area percentage of Fusarium inoculated seeds was significantly higher compared to uninoculated control. Nineteen isolates differed in their aggressiveness as the median disease area percentage ranged between 5.0 and 88.0% depending on isolate. The obtained isolates of four Fusarium species may be used in the future screening of soybean cultivars for resistance to these pathogens.

Faba Bean-Wheat Intercropping Can Control the Occurrence of Faba Bean Fusarium Wilt by Alleviating the Inhibitory Effect of Benzoic Acid on Disease Resistance Metabolism and the Expression of Resistance Genes

Background: Continuous cropping leads to the accumulation of autotoxic substances in faba beans, which limits their global production. Intercropping is widely used to alleviate these problems. Aim: This study aims to explore the important role of Fusarium oxysporum f. sp. fabae (FOF) and benzoic acid stress in enhancing the occurrence of faba bean Fusarium wilt and the potential mechanism of faba bean-wheat intercropping to control the occurrence of this disease. Methods: We analyzed the pathogenic mechanism of FOF and benzoic acid and the defense response of faba bean-wheat intercropping against the autotoxicity of benzoic acid under hydroponic conditions that included the pathogen alone and in combination with different concentrations of benzoic acid. Results: The dual stress of FOF and benzoic acid inhibited the activity of defensive enzymes, the synthesis of defensive substances, and the expression of defensive genes in faba bean roots and reduced the disease resistance of faba bean. This shows that benzoic acid plays an important role in helping FOF cause disease. Faba bean-wheat intercropping improves plant resistance by alleviating benzoic acid stress and reducing the incidence and disease index of Fusarium wilt. Conclusion: The dual stress of FOF and benzoic acid promotes the occurrence of faba bean Fusarium wilt by destroying the root defense system of faba bean. Faba bean-wheat intercropping can effectively alleviate the autotoxicity of benzoic acid and control the occurrence of Fusarium wilt by improving the physiological and biochemical resistance of faba beans and the expression of defense genes.

Evaluation of Pathogenic Fusarium spp. Associated with Soybean Seed (Glycine max) in Hubei Province, China

Soybean (Glycine max L.) seeds showing serious symptoms from rotted pods were collected from fields during the harvesting period (July to August 2020) in Taihu Farm, Jingzhou City, Hubei Province, China. Fusarium strains were frequently encountered during fungal isolation. According to the morphology and prepathogenicity tests, six strains showing variable effects on the seeds were selected for identification based on morphology and multilocus phylogenetic analysis of the internal transcribed spacer (ITS) region of the ribosomal DNA, translation elongation factor (EF-1α), calmodulin (CAM), β-tubulin (TUB), and partial RNA polymerase second largest subunit (RPB2), and to evaluate the pathogenic abilities on seed, root, and pod. The results indicated that the strains contained two species (Fusarium fujikuroi and F. proliferatum) in the Fusarium fujikuroi species complex (FFSC) and two species (F. luffae and F. sulawense) from the Fusarium incarnatum-equiseti species complex (FIESC). The two species of FFSC were more aggressive than those of FIESC on soybean seed, root, and pod. Among the strains, F. proliferatum YZU 201408 exhibited the most pathogenicity on all tests, with 72.2 to 90% disease severity.

Maize-soybean relay strip intercropping reshapes the rhizosphere bacterial community and recruits beneficial bacteria to suppress Fusarium root rot of soybean

Rhizosphere microbes play a vital role in plant health and defense against soil-borne diseases. Previous studies showed that maize-soybean relay strip intercropping altered the diversity and composition of pathogenic Fusarium species and biocontrol fungal communities in the soybean rhizosphere, and significantly suppressed soybean root rot. However, whether the rhizosphere bacterial community participates in the regulation of this intercropping on soybean root rot is not clear. In this study, the rhizosphere soil of soybean healthy plants was collected in the continuous cropping of maize-soybean relay strip intercropping and soybean monoculture in the fields, and the integrated methods of microbial profiling, dual culture assays in vitro, and pot experiments were employed to systematically investigate the diversity, composition, and function of rhizosphere bacteria related to soybean root rot in two cropping patterns. We found that intercropping reshaped the rhizosphere bacterial community and increased microbial community diversity, and meanwhile, it also recruited much richer and more diverse species of Pseudomonas sp., Bacillus sp., Streptomyces sp., and Microbacterium sp. in soybean rhizosphere when compared with monoculture. From the intercropping, nine species of rhizosphere bacteria displayed good antagonism against the pathogen Fusarium oxysporum B3S1 of soybean root rot, and among them, IRHB3 (Pseudomonas chlororaphis), IRHB6 (Streptomyces), and IRHB9 (Bacillus) were the dominant bacteria and extraordinarily rich. In contrast, MRHB108 (Streptomyces virginiae) and MRHB205 (Bacillus subtilis) were the only antagonistic bacteria from monoculture, which were relatively poor in abundance. Interestingly, introducing IRHB3 into the cultured substrates not only significantly promoted the growth and development of soybean roots but also improved the survival rate of seedlings that suffered from F. oxysporum infection. Thus, this study proves that maize-soybean relay strip intercropping could help the host resist soil-borne Fusarium root rot by reshaping the rhizosphere bacterial community and driving more beneficial microorganisms to accumulate in the soybean rhizosphere.

Nitrogen fertilization coupled with foliar application of iron and molybdenum improves shade tolerance of soybean under maize-soybean intercropping

Maize-soybean intercropping is practiced worldwide because of some of the anticipated advantages such as high crop yield and better utilization of resources (i.e., water, light, nutrients and land). However, the shade of the maize crop has a detrimental effect on the growth and yield of soybean under the maize-soybean intercropping system. Hence, this experiment was conducted to improve the shade tolerance of such soybean crops with optimal nitrogen (N) fertilization combined with foliar application of iron (Fe) and molybdenum (Mo). The treatments comprised five (5) maize-soybean intercropping practices: without fertilizer application (_F0), with N fertilizer application (_F1), with N fertilizer combined with foliar application of Fe (_F2), with N fertilizer coupled with foliar application of Mo (_F3) and with N fertilizer combined with foliar application of Fe and Mo (_F4). The findings of this study showed that maize-soybean intercropping under _F4 treatment had significantly (p< 0.05) increased growth indices such as leaf area (cm²), plant height (cm), stem diameter (mm), stem strength (g pot^-1), and internode length (cm) and yield indices (i.e., No of pods plant^-1, grain yield (g plant^-1), 100-grain weight (g), and biomass dry matter (g plant^-1)) of the soybean crop. Moreover, intercropping under _F4 treatment enhanced the chlorophyll SPAD values by 26% and photosynthetic activities such as Pn by 30%, gs by 28%, and Tr by 28% of the soybean crops, but reduced its CO₂ by 11%. Furthermore, maize-soybean intercropping under _F4 treatment showed improved efficiency of leaf chlorophyll florescence parameters of soybean crops such as Fv/Fm (26%), qp (17%), ϕPSII (20%), and ETR (17%), but reduced NPQ (12%). In addition, the rubisco activity and soluble protein content of the soybean crop increased by 18% in maize-soybean intercropping under _F4 treatment. Thus, this suggested that intercropping under optimal N fertilization combined with foliar application of Fe and Mo can improve the shade tolerance of soybean crops by regulating their chlorophyll content, photosynthetic activities, and the associated enzymes, thereby enhancing their yield and yield traits.

Changes in the Density and Composition of Rhizosphere Pathogenic Fusarium and Beneficial Trichoderma Contributing to Reduced Root Rot of Intercropped Soybean

The dynamic of soil-borne disease is closely related to the rhizosphere microbial communities. Maize–soybean relay strip intercropping has been shown to significantly control the type of soybean root rot that tends to occur in monoculture. However, it is still unknown whether the rhizosphere microbial community participates in the regulation of intercropped soybean root rot. In this study, rhizosphere Fusarium and Trichoderma communities were compared in either healthy or root-rotted rhizosphere soil from monocultured and intercropped soybean, and our results showed the abundance of rhizosphere Fusarium in intercropping was remarkably different from monoculture. Of four species identified, F. oxysporum was the most aggressive and more frequently isolated in diseased soil of monoculture. In contrast, Trichoderma was largely accumulated in healthy rhizosphere soil of intercropping rather than monoculture. T. harzianum dramatically increased in the rhizosphere of intercropping, while T. virens and T. afroharzianum also exhibited distinct isolation frequency. For the antagonism test in vitro, Trichoderma strains had antagonistic effects on F. oxysporum with the percentage of mycelial inhibition ranging from 50.59–92.94%, and they displayed good mycoparasitic abilities against F. oxysporum through coiling around and entering into the hyphae, expanding along the cell–cell lumen and even dissolving cell walls of the target fungus. These results indicate maize–soybean relay strip intercropping significantly increases the density and composition proportion of beneficial Trichoderma to antagonize the pathogenic Fusarium species in rhizosphere, thus potentially contributing to the suppression of soybean root rot under the intercropping.

Sugarcane–Peanut Intercropping System Enhances Bacteria Abundance, Diversity, and Sugarcane Parameters in Rhizospheric and Bulk Soils

Sugarcane–legume intercropping systems can effectively control pests and diseases as well as improve the fertility and health of farmland soil. However, little is known about the response of bacterial abundance, diversity, and community composition in the rhizosphere and non-rhizosphere soils under the sugarcane–peanut farming system. A field experiment was conducted with two treatments: sugarcane monoculture and sugarcane–peanut intercropping to examine the response of sugarcane parameters and edaphic factors. We also deciphered bacterial abundance, diversity, and community composition in the root endosphere, rhizosphere, and bulk soil by leveraging Illumina sequencing to conduct the molecular characterization of the 16S rRNA gene and nitrogenase (nifH) gene. We observed that sugarcane–peanut intercropping exhibited the advantages of tremendously increasing cane stalk height, stalk weight, and millable stalk number/20 m, and edaphic factors, namely, pH (1.13 and 1.93), and available phosphorus exhibited a fourfold and sixfold increase (4.66 and 6.56), particularly in the rhizosphere and bulk soils, respectively. Our result also showed that the sugarcane–peanut intercropping system significantly increased the bacterial richness of the 16S rRNA gene sequencing data by 13.80 and 9.28% in the bulk soil and rhizosphere soil relative to those in the monocropping sugarcane system, respectively. At the same time, sugarcane intercropping with peanuts significantly increased the Shannon diversity of nitrogen-fixing bacteria in the sugarcane rhizosphere soil. Moreover, most edaphic factors exhibited a positive regularity effect on bacterial community composition under the intercropping system. A linear discriminant analysis with effect size analysis of the 16S rRNA sequencing data revealed that bacteria in the root endosphere of the intercropped cane proliferated profoundly, primarily occupied by Devosia, Rhizobiales, Myxococcales, Allorhizobium-Neorhizobium-Pararhizobium-Rhizobium, Bradyrhizobium, and Sphingomonas. In conclusion, our findings demonstrated that sugarcane–peanut intercropping can enhance edaphic factors, sugarcane parameters, and bacterial abundance and diversity without causing adverse impacts on crop production and soil.

Maize intercropping enriches plant growth-promoting rhizobacteria and promotes both the growth and volatile oil concentration of Atractylodes lancea

In the Atractylodes lancea (A. lancea)-maize intercropping system, maize can promote the growth of A. lancea, but it is unclear whether this constitutes an aboveground or belowground process. In this study, we investigated the mechanisms of the root system interaction between A. lancea and maize using three different barrier conditions: no barrier (AI), nylon barrier (AN), and plastic barrier (AP) systems. The biomass, volatile oil concentration, physicochemical properties of the soil, and rhizosphere microorganisms of the A. lancea plant were determined. The results showed that (1) the A. lancea - maize intercropping system could promote the growth of A. lancea and its accumulation of volatile oils; (2) a comparison of the CK, AI, and AP treatments revealed that it was the above-ground effect of maize specifically that promoted the accumulation of both atractylon and atractylodin within the volatile oils of A. lancea, but inhibited the accumulation of hinesol and β-eudesmol; (3) in comparing the soil physicochemical properties of each treatment group, intercropping maize acidified the root soil of A. lancea, changed its root soil physicochemical properties, and increased the abundance of the acidic rhizosphere microbes of A. lancea at the phylum level; (4) in an analysis of rhizosphere microbial communities of A. lancea under different barrier systems, intercropping was found to promote plant growth-promoting rhizobacteria (PGPR) enrichment, including Streptomyces, Bradyrhizobium, Candidatus Solibacter, Gemmatirosa, and Pseudolabrys, and the biomass of A. lancea was significantly influenced by PGPR. In summary, we found that the rhizosphere soil of A. lancea was acidified in intercropping with maize, causing the accumulation of PGPR, which was beneficial to the growth of A. lancea.

Sugarcane-Legume Intercropping Can Enrich the Soil Microbiome and Plant Growth

Soil microbes have a direct impact on plant metabolism and health. The current study investigates the comparative rhizobiome between sugarcane monoculture and sugarcane–soybean intercropping. A greenhouse experiment was performed with two treatments: (1) sugarcane monoculture and (2) sugarcane–soybean intercropped. We used a high-throughput sequencing (HTS) platform to analyze the microbial community. We used the 16S rRNA gene and internal transcribed spacer region primers to identify the microbial diversity. HTS results revealed that a total of 2,979 and 124 bacterial and fungal operational taxonomic units (OTUs) were observed, respectively. Microbial diversity results concluded that the intercropping system has a beneficial impact on soil microbes. The highest numbers of bacterial and fungal OTUs were found in the intercropping system, and these results also collaborated with quantitative PCR results. Additionally, intercropped sugarcane plants showed a higher weight of above- and below-ground parts than the monoculture. Soil chemical analysis results also complemented that the intercropping system nourished organic carbon, total nitrogen, and soil enzyme activities. Correlation analysis of the diversity index and abundance concluded that soil nutrient content positively influenced the microbial abundance that improves plant growth. The present study frames out the profound insights of microbial community interaction under the sugarcane–soybean intercropping system. This information could help improve or increase the sugarcane crop production without causing any negative impact on sugarcane plant growth and development.

Transcriptional Responses of Fusarium graminearum Interacted with Soybean to Cause Root Rot

Fusarium graminearum is the most devastating pathogen of Fusarium head blight of cereals, stalk and ear of maize, and it has recently become a potential threat for soybean as maize-soybean strip relay intercropping is widely practiced in China. To elucidate the pathogenesis mechanism of F. graminearum on intercropped soybean which causes root rot, transcriptional profiling of F. graminearum at 12, 24, and 48 h post-inoculation (hpi) on soybean hypocotyl tissues was conducted. In total, 2313 differentially expressed genes (DEGs) of F. graminearum were annotated by both KEGG pathway and Gene Ontology (GO) analysis. Among them, 128 DEGs were commonly expressed at three inoculation time points while the maximum DEGs were induced at 24 hpi. In addition, DEGs were also rich in carbon metabolism, ribosome and peroxisome pathways which might contribute to carbon source utilization, sexual reproduction, virulence and survival of F. graminearum when infected on soybean. Hence, this study will provide some basis for the deep understanding the pathogenesis mechanism of F. graminearum on different hosts and its effective control in maize-soybean strip relay intercropping systems.

Symptoms and pathogens diversity of Corn Fusarium sheath rot in Sichuan Province, China

To elucidate the symptoms and pathogens diversity of corn Fusarium sheath rot (CFSR), diseased samples were collected from 21 county-level regions in 12 prefecture-level districts of Sichuan Province from 2015 to 2018 in the present study. In the field, two symptom types appeared including small black spots with a linear distribution and wet blotches with a tawny or brown color. One hundred thirty-seven Fusarium isolates were identified based on morphological characteristics and phylogenetic analysis (EF1-α), and Koch's postulates were also assessed. The results identified the isolates as 8 species in the Fusarium genus, including F. verticillioides, F. proliferatum, F. fujikuroi, F. asiaticum, F. equiseti, F. meridionale, F. graminearum and F. oxysporum, with isolation frequencies of 30.00, 22.67, 15.33, 7.33, 6.00, 5.33, 3.33 and 1.33%, respectively. Fusarium verticillioides and F. proliferatum were the dominant and subdominant species, respectively. Two or more Fusarium species such as F. verticillioides and F. proliferatum were simultaneously identified at a mixed infection rate of 14.67% in the present study. The pathogenicity test results showed that F. proliferatum and F. fujikuroi exhibited the highest virulence, with average disease indices of 30.28 ± 2.87 and 28.06 ± 1.96, followed by F. equiseti and F. verticillioides, with disease indices of 21.48 ± 2.14 and 16.21 ± 1.84, respectively. Fusarium asiaticum, F. graminearum and F. meridonale showed lower virulence, with disease indices of 13.80 ± 2.07, 11.57 ± 2.40 and 13.89 ± 2.49, respectively. Finally, F. orysporum presented the lowest virulence in CFSR, with a disease index of 10.14 ± 1.20. To the best of our knowledge, this is the first report of F. fujikuroi, F. meridionale and F. asiaticum as CFSR pathogens in China.