Diversity of the Seedborne Fungi and Pathogenicity of Fusarium Species Associated with Intercropped Soybean

The Diversity of Seed-Borne Fungi Associated with Soybean Grown in Southern Poland

Fungi have the potential to colonize soybean seeds in the field, during their maturation in the pods and after harvest, during storage. The aim of this study was to identify fungi inhabiting soybean seeds after storage with varying germination capacity and to evaluate their chemical composition. The research material consisted of twelve soybean seed lots collected from the fields in southern Poland and stored over winter. The germination percentage of these lots ranged between 20.67% and 81.33%. The seeds were subjected to analyses of the main chemical components and mycological analysis. Fungal isolates were subjected to taxonomic identification using microscopic methods and DNA sequencing (using internal transcribed spacer region and secondary barcoding regions). A total number of 355 fungal isolates from 16 genera were identified, with Aspergillus, Alternaria, and Fusarium being the most common. Species were successfully identified in 94% of isolates. Twelve examined seed lots varied significantly in the number of isolated fungal species (from 1 to 17). Moreover, they also differed in the isolated species composition. Highly significant positive correlation was found between the number of Aspergillus psedudoglaucus isolates and the content of free fatty acids. In turn, the number of Fusarium spp. isolates correlated negatively with protein and nitrogen content. Similarly, highly significant negative correlation was found between the number of all fungal isolates and the 1000-seed weight, indicating that smaller seeds are more vulnerable to fungal infection. The results obtained in this study identify species of fungi which may be responsible for lowering quality of the seeds obtained in southern Poland.

Nano-enhanced defense: Titanium-enriched Alginate-Bentonite coating augments Bacillus amyloliquefaciens D203 efficacy against Magnaporthe oryzae in Kenyan rice cultivation

Rice blast disease, caused by Magnaporthe oryzae, poses a significant threat to global rice production, necessitating the development of effective and sustainable management strategies. Biological control using beneficial microbes like Bacillus amyloliquefaciens has emerged as a promising approach due to its ability to enhance plant resistance and reduce disease incidence. Nano-encapsulation of bacteria, which involves embedding beneficial microbes within nanomaterials, offers a novel method to improve the stability, survival, and efficacy of these biocontrol agents. This study evaluated the capacity of encapsulated Bacillus amyloliquefaciens D203, embedded within an alginate-bentonite coating infused with titanium nanoparticles (TNs), to stimulate defense responses in rice seedlings challenged by the Magnaporthe oryzae the causal agent of rice blast disease. Encapsulation was achieved using the extrusion technique, with some modifications. Using a completely randomized design, the experiment was conducted in a greenhouse, with four treatments replicated four times. The experiment used the popular Kenyan rice variety "BASMATI 370". The study investigated the impact of strain D203 on the incidence, severity, and area under disease progress curves related to M. oryzae, as well as the expression of defense-related enzymes. The results demonstrated that rice plants derived from seeds coated with the D203 encapsulated B. amyloliquefaciens strain exhibited higher levels of defense-related enzyme expression, including peroxidase (POD), phenylalanine ammonia-lyase (PAL), superoxide dismutase (SOD) and catalase (CAT), compared to controls. In addition, the incidence and severity of the disease were markedly lower in plants treated with encapsulated B. amyloliquefaciens compared to controls, sometimes paralleling the efficacy of hexaconazole treatment. These findings suggest that the encapsulation of strain D203 has the potential to enhance resistance against rice blast disease by inducing systemic resistance through the production of antioxidant enzymes.

Genetic Diversity and Pathogenicity of the Fusarium Species Complex on Soybean in Serbia

Using morphological and cultural characteristics for identification, 36 Fusarium isolates were recovered from diseased roots, stems, and seeds of soybean from several localities throughout Vojvodina Province, Serbia. Based on molecular characterization, 12 Fusarium species were identified: F. acuminatum, F. avenaceum, F. commune, F. equiseti, F. graminearum, F. incarnatum, F. oxysporum, F. proliferatum, F. solani, F. sporotrichioides, F. subglutinans, and F. tricinctum. The elongation factor 1-α-based phylogeny grouped the isolates into 12 well-supported clades, but polymorphisms among sequences in some clades suggested the use of the species complex concept: (i) F. incarnatum-equiseti species complex (FIESC)-F. incarnatum and F. equiseti; (ii) F. oxysporum species complex (FOSC)-F. oxysporum; (iii) F. solani species complex (FSSC)-F. solani; and (iv) F. acuminatum/F. avenaceum/F. tricinctum species complex (FAATSC)-F. acuminatum, F. avenaceum, and F. tricinctum. Pathogenicity tests showed that the most aggressive species causing soybean seed rot were F. sporotrichioides, F. graminearum, FIESC, and F. avenaceum. Furthermore, F. subglutinans, FSSC, and F. proliferatum showed a high percentage of pathogenicity on soybean seeds (80 to 100%), whereas variability in pathogenicity occurred within isolates of F. tricinctum. FOSC, F. commune, and F. acuminatum had the lowest pathogenicity. To our knowledge, this is the first study of the characterization of Fusarium species on soybean in Serbia. This study provides valuable information about the composition of Fusarium species and pathogenicity that will be used in further research on soybean resistance to Fusarium-based diseases.

Impact of Foliar Fungicide Application on the Culturable Fungal Endophyte Community of Soybean Seed in the Midwest United States

The purpose of our study was to determine whether the application of quinone outside inhibitor (QoI) and pyrazole-carboxamide fungicides as a tank mix would impact the endophyte community of soybean seed. Field trials during 2018 in Iowa, South Dakota, and Wisconsin, U.S.A., investigated the impact of a single combination fungicide spray at early pod set in soybeans. The composition of culturable endophytic fungi in mature soybean seed was assessed on three cultivars per state, with maturity groups (MGs) ranging from 1.1 to 4.7. An unusually wet 2018 season delayed harvest, which led to a high level of fungal growth in grain. The survey included 1,080 asymptomatic seeds that were disinfested and individually placed on 5-cm-diameter Petri plates of acidified water agar. The survey yielded 721 fungal isolates belonging to 24 putative species in seven genera; taxa were grouped into genera based on a combination of morphological and molecular evidence. The dominant genera encountered in the survey were Alternaria, Diaporthe, and Fusarium. The study showed that the fungicide treatment reduced the incidence of Fusarium in Wisconsin seed, increased the incidence of Diaporthe in seed from all states, and had no impact on the incidence of Alternaria. This is one of the first attempts to characterize the diversity of seed endophytes in soybean and the first to characterize the impacts of fungicide spraying on these endophyte communities across three states. Our study provides evidence that the impact of a fungicide spray on soybean seed endophyte communities may be influenced by site, weather, and cultivar maturity group.

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.

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.

Physiological and metabolic analyses provide insight into soybean seed resistance to fusarium fujikuroi causing seed decay

Seed-borne pathogens cause diverse diseases at the growth, pre- and post-harvest stage of soybean resulting in a large reduction in yield and quality. The physiological and metabolic aspects of seeds are closely related to their defense against pathogens. Recently, Fusarium fujikuroi has been identified as the dominant seed-borne fungi of soybean seed decay, but little information on the responses of soybean seeds induced by F. fujikuroi is available. In this study, a time-course symptom development of seed decay was observed after F. fujikuroi inoculation through spore suspension soaking. The germination rate and the contents of soluble sugar and soluble protein were significantly altered over time. Both chitinase and β-1,3-glucanase as important fungal cell wall-degrading enzymes of soybean seeds were also rapidly and transiently activated upon the early infection of F. fujikuroi. Metabolic profile analysis showed that the metabolites in glycine, serine, and threonine metabolism and tryptophan metabolism were clearly induced by F. fujikuroi, but different metabolites were mostly enriched in isoflavone biosynthesis, flavone biosynthesis, and galactose pathways. Interestingly, glycitein and glycitin were dramatically upregulated while daidzein, genistein, genistin, and daidzin were largely downregulated. These results indicate a combination of physiological responses, cell wall-related defense, and the complicated metabolites of soybean seeds contributes to soybean seed resistance against F. fujikuroi, which are useful for soybean resistance breeding.

Genome-wide characterization of soybean RALF genes and their expression responses to Fusarium oxysporum

RALFs (RAPID ALKALINIZATION FACTORs) are small peptides required for plant growth, development and immunity. RALF has recently been discovered to regulate plant resistance to fungal infection. However, little is known in crops, particularly in soybean. Here, 27 RALFs were identified in the genome of Glycine max. All Glycine max RALFs (GmRALFs) and 34 Arabidopsis RALFs were classified into 12 clades via the phylogenetic analyses. Gene structures, conserved motifs, chromosome distribution and cis-elements were analyzed in this study. Furthermore, 18 GmRALFs were found in response to Fusarium oxysporum (F. oxysporum) infection in soybean and to have distinct expression patterns. Among them, secretory function of two GmRALFs were identified, and three GmRALFs were detected to interact with FERONIA in Glycine max (GmFERONIA, GmFER). Our current study systematically identified and characterized GmRALFs in the soybean genome, laying a groundwork for further functional analyses and soybean breeding.

Identification of New Fusarium sulawense Strains Causing Soybean Pod Blight in China and Their Control Using Carbendazim, Dipicolinic Acid and Kojic Acid

Soybean plants are highly susceptible to Fusarium species, which significantly reduce soybean production and quality. Several Fusarium species have been reported to synthesize mycotoxins, such as trichothecene, which have been related to major human diseases. In November 2021, soybean pods in Nantong municipality, China, showed black necrotic lesions during the harvest stage. The disease incidence reached 69%. The pathogen was identified as Fusarium sulawense via morphological analysis and sequencing of ITS, EF1-α and RPB2 genes. A PCR assay with primers targeting the trichothecene biosynthesis genes suggested that the three isolates could synthesize trichothecenes. The effectiveness of fungicide carbendazim and natural metabolites dipicolinic acid and kojic acid was screened for the management of F. sulawense on postharvest soybean pods. The highest efficacy was obtained when combining 3.8 mg/mL carbendazim and 0.84 mg/mL dipicolinic acid (curative efficacy: 49.1% lesion length inhibition; preventive efficacy: 82.7% lesion length inhibition), or 1.9 mg/mL carbendazim and 0.71 mg/mL kojic acid (preventive efficacy: 84.9% lesion length inhibition). Collectively, this report will lead to a better understanding of the safety hazards found in soybean products in China and reveals the application of dipicolinic and kojic acids to reduce the use of carbendazim.

Ecology and diversity of culturable fungal species associated with soybean seedling diseases in the Midwestern United States

AIMS

To isolate and characterize fungi associated with diseased soybean seedlings in Midwestern soybean production fields and to determine the influence of environmental and edaphic factors on their incidence.

METHODS AND RESULTS

Seedlings were collected from fields with seedling disease history in 2012 and 2013 for fungal isolation. Environmental and edaphic data associated with each field was collected. 3036 fungal isolates were obtained and assigned to 76 species. The most abundant genera recovered were Fusarium (73%) and Trichoderma (11.2%). Other genera included Mortierella, Clonostachys, Rhizoctonia, Alternaria, Mucor, Phoma, Macrophomina and Phomopsis. Most recovered species are known soybean pathogens. However, non-pathogenic organisms were also isolated. Crop history, soil density, water source, precipitation and temperature were the main factors influencing the abundance of fungal species.

CONCLUSION

Key fungal species associated with soybean seedling diseases occurring in several US production regions were characterized. This work also identified major environment and edaphic factors affecting the abundance and occurrence of these species.

SIGNIFICANCE AND IMPACT OF THE STUDY

The identification and characterization of the main pathogens associated with seedling diseases across major soybean-producing areas could help manage those pathogens, and devise more effective and sustainable practices to reduce the damage they cause.

The Application of Terahertz Time-Domain Spectroscopy to Identification of Potato Late Blight and Fusariosis

Fusarium and late blight (fungal diseases of cereals and potatoes) are among the main causes of crop loss worldwide. A key element of success in the fight against phytopathogens is the timely identification of infected plants and seeds. That is why the development of new methods for identifying phytopathogens is a priority for agriculture. The terahertz time-domain spectroscopy (THz-TDS) is a promising method for assessing the quality of materials. For the first time, we used THz-TDS for assessing the infection of seeds of cereals (oats, wheat and barley) with fusarium and potato tubers of different varieties (Nadezhda and Meteor) with late blight. We evaluated the refractive index, absorption coefficient and complex dielectric permittivity in healthy and infected plants. The presence of phytopathogens on seeds was confirmed by microscopy and PCR. It is shown, that Late blight significantly affected all the studied spectral characteristics. The nature of the changes depended on the variety of the analyzed plants and the localization of the analyzed tissue relative to the focus of infection. Fusarium also significantly affected all the studied spectral characteristics. It was found that THz-TDS method allows you to clearly establish the presence or absence of a phytopathogens, in the case of late blight, to assess the degree and depth of damage to plant tissues.

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.

Influence of Peanut, Sorghum, and Soil Salinity on Microbial Community Composition in Interspecific Interaction Zone

Soil microorganisms play important roles in crop production and sustainable agricultural management. However, soil conditions and crop selection are key determining factors for soil microbial communities. This study investigated the effect of plant types and soil salinity on the microbial community of interspecific interaction zone (II) based on the sorghum/peanut intercropping system. Microbial community diversity and composition were determined through PacBio single molecule, real-time sequencing of 16S rDNA and internal transcribed spacer (ITS) genes. Results showed Proteobacteria, Bacteroidota, and Acidobacteriota to be the dominant bacterial phyla in IP, II, and IS, whereas Ascomycota, Basidiomycota, and Mucoromycota were the dominant fungal phyla. Under salt-treated soil conditions, the plants-specific response altered the composition of the microbial community (diversity and abundance). Additionally, the interspecific interactions were also helpful for maintaining the stability and ecological functions of microbial communities by restructuring the otherwise stable core microbiome. The phylogenetic structure of the bacterial community was greatly similar between IP and II while that of the fungal community was greatly similar between IP and IS; however, the phylogenetic distance between IP and IS increased remarkably upon salinity stress. Overall, salinity was a dominant factor shaping the microbial community structure, although plants could also shape the rhizosphere microenvironment by host specificity when subjected to environmental stresses. In particular, peanut still exerted a greater influence on the microbial community of the interaction zone than sorghum.

Evaluation of Seven Essential Oils as Seed Treatments against Seedborne Fungal Pathogens of Cucurbita maxima

Essential oils are gaining interest as environmentally friendly alternatives to synthetic fungicides for management of seedborne pathogens. Here, seven essential oils were initially tested in vivo for disinfection of squash seeds (Cucurbita maxima) naturally contaminated by Stagonosporopsis cucurbitacearum, Alternaria alternata, Fusarium fujikuro, Fusarium solani, Paramyrothecium roridum, Albifimbria verrucaria, Curvularia spicifera, and Rhizopus stolonifer. The seeds were treated with essential oils from Cymbopogon citratus, Lavandula dentata, Lavandula hybrida, Melaleuca alternifolia, Laurus nobilis, and Origanum majorana (#1 and #2). Incidence of S. cucurbitacearum was reduced, representing a range between 67.0% in L. nobilis to 84.4% in O. majorana #2. Treatments at 0.5 mg/mL essential oils did not affect seed germination, although radicles were shorter than controls, except with C. citratus and O. majorana #1 essential oils. Four days after seeding, seedling emergence was 20%, 30%, and 10% for control seeds and seeds treated with C. citratus essential oil (0.5 mg/mL) and fungicides (25 g/L difenoconazole plus 25 g/L fludioxonil). S. cucurbitacearum incidence was reduced by ~40% for plantlets from seeds treated with C. citratus essential oil. These data show the effectiveness of this essential oil to control the transmission of S. cucurbitacearum from seeds to plantlets, and thus define their potential use for seed decontamination in integrated pest management and organic agriculture.

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.