Patterns of Diversity of Fusarium Fungi Contaminating Soybean Grains

Measurement of the effectiveness of Clonostachys rosea in reducing Fusarium biomass on wheat straw

The survival and growth of plant pathogens on crop residues are key factors facilitating the dynamics of crop diseases. Spores (e.g., perithecia, and chlamydospores) and mycelium of pathogenic fungi overwinter on harvest residues, such as straw, and serve as initial inoculum infecting crops in the next growing season. Therefore, targeting overwintering fungi is essential to attaining effective disease control. Beneficial microorganisms offer advantages in controlling pathogens through their ability to colonize and exploit different environmental niches. In this study, we applied qPCR assays to explore the biocontrol performance of locally isolated strains of Clonostachys against various Fusarium pathogens. We proved that prior colonization of wheat straw by Fusarium spp. can be effectively reduced by Clonostachys rosea. We demonstrated that the efficiency of C. rosea to reduce Fusarium inoculum appears to remain at a similar level for most studied strains regardless of the target pathogen and the level of colonization of substrates by pathogens. Efficient performance of local C. rosea strains identifies possible targets for future strategies to control Fusarium diseases in cereals. Our study also highlights the challenge in sequence-based determination of C. rosea, which is crucial for the efficient selection of beneficial strains for biocontrol purposes.

A fungal P450 enzyme from Fusarium equiseti HG18 with 7β-hydroxylase activity in biosynthesis of ursodeoxycholic acid

Cytochrome P450 enzyme with 7β-hydroxylation capacity has attracted widespread attentions due to the vital roles in the biosynthesis of ursodeoxycholic acid (UDCA), a naturally active molecule for the treatment of liver and gallbladder diseases. In this study, a novel P450 hydroxylase (P450FE) was screen out from Fusarium equiseti HG18 and identified by a combination of genome and transcriptome sequencing, as well as heterologous expression in Pichia pastoris. The biotransformation of lithocholic acid (LCA) by whole cells of recombinant Pichia pastoris further confirmed the C7β-hydroxylation with 5.2% UDCA yield. It was firstly identified a fungal P450 enzyme from Fusarium equiseti HG18 with the capacity to catalyze the LCA oxidation producing UDCA. The integration of homology modeling and molecular docking discovered the substrate binding to active pockets, and the key amino acids in active center were validated by site-directed mutagenesis, and revealed that Q112, V362 and L363 were the pivotal residues of P450FE in regulating the activity and selectivity of 7β-hydroxylation. Specifically, V362I mutation exhibited 2.6-fold higher levels of UDCA and higher stereospecificity than wild-type P450FE. This advance provided guidance for improving the catalytic efficiency and selectivity of P450FE in LCA hydroxylation, indicative of the great potential in green synthesis of UDCA from biologically toxic LCA.

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.

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.

Genetic Diversity and Population Structure of Head Blight Disease Causing Fungus Fusarium graminearum in Northern Wheat Belt of India

Head blight or scab caused by Fusarium graminearum (FG), once ranked as a minor disease in wheat, is now emerging as one of the economically important diseases in India. The present study represents the first in-depth population genetic analysis of the FG from the northern wheat belt of India. In this study, multiple conserved gene sequences comprised of β-tubulin (TUB), translation elongation factor 1-α (TEF), and histone-3 (HIS) regions were used for multi-locus phylogenetic analysis of 123 geographically distinct F. graminearum isolates collected from four different states (Haryana (HR), Punjab (PB), Rajasthan (RJ) and West Bengal (WB)) of India. The phylogenetic and haplotype analysis showed the presence of thirty haplotypes in all the analyzed populations. The haplotypic diversity in the RJ population (Hd = 0.981) was higher than in the HR (Hd = 0.972), PB (Hd = 0.965) and WB population (Hd = 0.962). Recombination events (Rm = 12) and mutation events (485) were also detected. Analysis of molecular variance (AMOVA) indicated that genetic diversity was exclusively due to the differences within populations. The haplotype network was widely dispersed and not associated with specific populations, as a single common haplotype was not detected. The PB population contained both unique (H9, H10 and H11) and shared haplotypes (27 haplotypes) in a higher number in comparison to other geographical locations. Except for haplotype H22 (contains highly aggressive isolates), there was no specific linkage noticed between the isolate aggressiveness and haplotype. The concatenated sequences of all the three genes demonstrated a low level of genetic differentiation (Fst = −0.014 to 0.02) in the analyzed population. Positive values for the neutrality tests in PB, HR and RJ reveal a balancing selection mechanism behind the FG population structure. The WB population showed both positive and negative values of neutrality indices, indicating the role of both population expansion as well as balancing selection in structuring the FG population.