Fusarium Root Rot Complex in Soybean: Molecular Characterization, Trichothecene Formation, and Cross-Pathogenicity

Decoding the biochemical dialogue: metabolomic insights into soybean defense strategies against diverse pathogens

Soybean, a crucial global leguminous crop, confronts persistent threats from diverse pathogens, exerting a profound impact on global yields. While genetic dimensions of soybean-pathogen interactions have garnered attention, the intricate biochemical responses remain poorly elucidated. In this study, we applied targeted and untargeted liquid chromatography coupled to mass spectrometry (LC-MS) metabolite profiling to dissect the complex interplay between soybeans and five distinct pathogens. Our analysis uncovered 627 idMS/MS spectra, leading to the identification of four main modules, encompassing flavonoids, isoflavonoids, triterpenoids, and amino acids and peptides, alongside other compounds such as phenolics. Profound shifts were observed in both primary and secondary metabolism in response to pathogenic infections. Particularly notable were the bidirectional changes in total flavonoids across diverse pathogenic inoculations, while triterpenoids exhibited a general declining trend. Noteworthy among the highly inducible total flavonoids were known representative anti-pathogen compounds (glyceollin I), backbone forms of isoflavonoids (daidzein, genistein, glycitein, formononetin), and newly purified compounds in this study (prunin). Subsequently, we delved into the biological roles of these five compounds, validating their diverse functions against pathogens: prunin significantly inhibited the vegetative growth and virulence of Phytophthora sojae; genistein exhibited a pronounced inhibitory effect on the vegetative growth and virulence of Phomopsis longicolla; daidzein and formononetin displayed significant repressive effects on the virulence of P. longicolla. This study underscores the potent utility of metabolomic tools, providing in-depth insights into plant-pathogen interactions from a biochemical perspective. The findings not only contribute to plant pathology but also offer strategic pathways for bolstering plant resistance against diseases on a broader scale.

Resistance mechanism of Phomopsis longicolla to fludioxonil is associated with modifications in PlOS1, PlOS4 and PlOS5

Phomopsis longicolla, a causal agent of soybean root rot, stem blight, seed decay, pod and stem canker, which seriously affects the yield and quality of soybean production worldwide. The phenylpyrrole fungicide fludioxonil exhibits a broad spectrum and high activity against phytopathogenic fungi. In this study, the baseline sensitivity of 100 P. longicolla isolates collected from the main soybean production areas of China to fludioxonil were determined. The result showed that the EC50 values of all the P. longicolla isolates ranged from 0.013 to 0.035 μg/ml. Furthermore, 12 fludioxonil-resistance (FluR) mutants of P. longicolla were generated from 6 fludioxonil-sensitive (FluS) isolates. and the resistance factors (RF) of 12 FluR mutants were >3500. Sequence alignment showed that multiple mutation types were found in PlOS1, PlOS4 or/and PlOS5 of FluR mutants. All the FluR mutants exhibited fitness penalty in mycelial growth, conidiation, virulence and osmo-adaptation. Under fludioxonil or NaCl treatment condition, the glycerol accumulation was significantly increased in FluS isolates, but was slightly increased in FluR mutants, and the phosphorylation level of most FluR mutants was significantly decreased when compared to the FluS isolates. Additionally, positive cross-resistance was observed between fludioxonil and procymidone but not fludioxonil and pydiflumetofen, pyraclostrobin or fluazinam. This is first reported that the baseline sensitivity of P. longicolla to fludioxonil, as well as the biological and molecular characterizations of P. longicolla FluR mutants to fludioxonil. These results can provide scientific directions for controlling soybean diseases caused by P. longicolla using fludioxonil.

Pathogenicity, Host Resistance, and Genetic Diversity of Fusarium Species under Controlled Conditions from Soybean in Canada

Fusarium spp. are commonly associated with the root rot complex of soybean (Glycine max). Previous surveys identified six common Fusarium species from Manitoba, including F. oxysporum, F. redolens, F. graminearum, F. solani, F. avenaceum, and F. acuminatum. This study aimed to determine their pathogenicity, assess host resistance, and evaluate the genetic diversity of Fusarium spp. isolated from Canada. The pathogenicity of these species was tested on two soybean cultivars, 'Akras' (moderately resistant) and 'B150Y1' (susceptible), under greenhouse conditions. The aggressiveness of the fungal isolates varied, with root rot severities ranging from 1.5 to 3.3 on a 0-4 scale. Subsequently, the six species were used to screen a panel of 20 Canadian soybean cultivars for resistance in a greenhouse. Cluster and principal component analyses were conducted based on the same traits used in the pathogenicity study. Two cultivars, 'P15T46R2' and 'B150Y1', were consistently found to be tolerant to F. oxysporum, F. redolens, F. graminearum, and F. solani. To investigate the incidence and prevalence of Fusarium spp. in Canada, fungi were isolated from 106 soybean fields surveyed across Manitoba, Saskatchewan, Ontario, and Quebec. Eighty-three Fusarium isolates were evaluated based on morphology and with multiple PCR primers, and phylogenetic analyses indicated their diversity across the major soybean production regions of Canada. Overall, this study contributes valuable insights into host resistance and the pathogenicity and genetic diversity of Fusarium spp. in Canadian soybean fields.

Distribution and Pathogenicity of Fusarium Species Associated with Soybean Root Rot in Northeast China

Fusarium root rot is an increasingly severe problem in soybean cultivation. Although several Fusarium species have been reported to infect soybean roots in Heilongjiang province, their frequency and aggressiveness have not been systematically quantified in the region. This study aimed to investigate the diversity and distribution of Fusarium species that cause soybean root rot in Heilongjiang province over two years. A total of 485 isolates belonging to nine Fusarium species were identified, with F. oxysporum and F. solani being the most prevalent. Pot experiments were conducted to examine the relative aggressiveness of different Fusarium species on soybean roots, revealing that F. oxysporum and F. solani were the most aggressive pathogens, causing the most severe root rot symptoms. The study also assessed the susceptibility of different soybean cultivars to Fusarium root rot caused by F. oxysporum and F. solani. The results indicated that the soybean cultivar DN51 exhibited the most resistance to both pathogens, indicating that it may possess genetic traits that make it less susceptible to Fusarium root rot. These findings provide valuable insights into the diversity and distribution of Fusarium species that cause soybean root rot and could facilitate the development of effective management strategies for this disease.

Maize plant expresses SWEET transporters differently when interacting with Trichoderma asperellum and Fusarium verticillioides, two fungi with different lifestyles

Most Trichoderma species are beneficial fungi that promote plant growth and resistance, while Fusarium genera cause several crop damages. During the plant-fungi interaction there is a competition for sugars in both lifestyles. Here we analyzed the plant growth promotion and biocontrol activity of T. asperellum against F. verticillioides and the effect of both fungi on the expression of the maize diffusional sugar transporters, the SWEETs. The biocontrol activity was done in two ways, the first was by observing the growth capacity of both fungus in a dual culture. The second one by analyzing the infection symptoms, the chlorophyl content and the transcript levels of defense genes determined by qPCR in plants with different developmental stages primed with T. asperellum conidia and challenged with F. verticillioides. In a dual culture, T. asperellum showed antagonist activity against F. verticillioides. In the primed plants a delay in the infection disease was observed, they sustained chlorophyll content even after the infection, and displayed upregulated defense-related genes. Additionally, the T. asperellum primed plants had longer stems than the nonprimed plants. SWEETs transcript levels were analyzed by qPCR in plants primed with either fungus. Both fungi affect the transcript levels of several maize sugar transporters differently. T. asperellum increases the expression of six SWEETs on leaves and two at the roots and causes a higher exudation of sucrose, glucose, and fructose at the roots. On the contrary, F. verticillioides reduces the expression of the SWEETs on the leaves, and more severely when a more aggressive strain is in the plant. Our results suggest that the plant is able to recognize the lifestyle of the fungi and respond accordingly by changing the expression of several genes, including the SWEETs, to establish a new sugar flux.

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.

Structure and ecological function of the soil microbiome associated with 'Sanghuang' mushrooms suffering from fungal diseases

BACKGROUND

The most serious challenges in medicinal 'Sanghuang' mushroom production are the fungal diseases caused by various molds. Application of biological agents has been regarded as a potential crop disease management strategy. Here, the soil microbiome associated with 'Sanghuang' mushroom affected by fungal diseases grown under field cultivation (FC) and hanging cultivation (HC) was characterized using culture-dependent and culture-independent methods.

RESULTS

A total of 12,525 operational taxonomic units (OTUs) and 168 pure cultures were obtained using high-throughput sequencing and a culture-dependent method, respectively. From high-throughput sequencing, we found that HC samples had more OTUs, higher α-diversity, and greater microbial community complexity than FC samples. Analysis of β-diversity divided the soil microbes into two groups according to cultivation mode. Basidiomycota (48.6%) and Ascomycota (46.5%) were the two dominant fungal phyla in FC samples, with the representative genera Trichoderma (56.3%), Coprinellus (29.4%) and Discosia (4.8%), while only the phylum Ascomycota (84.5%) was predominant in HC samples, with the representative genera Discosia (34.0%), Trichoderma (30.2%), Penicillium (14.9%), and Aspergillus (7.8%). Notably, Trichoderma was predominant in both the culture-independent and culture-dependent analyses, with Trichoderma sp. FZ0005 showing high host pathogenicity. Among the 87 culturable bacteria, 15 exhibited varying extents of antifungal activity against Trichoderma sp. FZ0005, with three strains of Bacillus spp. (HX0037, HX0016, and HX0039) showing outstanding antifungal capacity.

CONCLUSIONS

Overall, our results suggest that Trichoderma is the major causal agent of 'Sanghuang' fungal diseases and that Bacillus strains may be used as biocontrol agents in 'Sanghuang' cultivation.

Role of FoERG3 in Ergosterol Biosynthesis by Fusarium oxysporum and the Associated Regulation by Bacillus subtilis HSY21

Ergosterol is an important component of the fungal cell membrane and represents an effective target of chemical pesticides. However, the current understanding of ergosterol biosynthesis in the soybean root rot pathogen Fusarium oxysporum remains limited. In addition, the regular use of fungicides that inhibit ergosterol synthesis will seriously harm the ecological environment and human health. Bacillus subtilis is gradually replacing chemical control as a safe and effective biological agent; to investigate its effect on ergosterol synthesis of F. oxysporum, we verified the biological function of the FoERG3 gene of F. oxysporum by constructing knockout mutants. The results showed that knocking out FoERG3 blocked ergosterol biosynthesis, restricted mycelial growth, and increased the sensitivity to external stressors (NaCl, D-sorbitol, Congo Red, and H₂O₂). The increased permeability of the cell membrane promoted increased extracellular K⁺ levels and decreased mitochondrial cytochrome C contents. Treatment with suspension of B. subtilis HSY21 cells resulted in similar damage as observed when treating FoERG3-knockout F. oxysporum cells with ergosterol, which was characterised by deformity and swelling of the mycelium surface; increased membrane permeability; decreased pathogenicity to soybeans; and significantly decreased activities of cellulase, β-glucosidase, amylase, and pectin-methyl galactosylase. Notably, deleting FoERG3 resulted in a significant lag in the defense-response time of soybeans. Our results suggest that FoERG3 strongly influences the virulence of F. oxysporum and may be used as a potential antimicrobial target by B. subtilis HSY21 to inhibit ergosterol synthesis, which supports the use of B. subtilis as a biological control agent for protecting against F. oxysporum infection.

Specific Detection and Quantification of Major Fusarium spp. Associated with Cereal and Pulse Crops

Plant pathogenic Fusarium spp. are widespread and cause important diseases on a wide host range, including economically important cereal and pulse crops. A number of molecular methods have been used to detect, identify, and quantify a long list of plant pathogenic Fusarium spp. In general, these methods are much faster, highly specific, more sensitive, and more accurate than culture-based methods and can be performed and interpreted by personnel with no specialized taxonomical expertise. The accurate isolation and identification of these pathogens is required to effectively manage diseases caused by pathogenic Fusarium spp. In this chapter, we present detailed molecular methods for detection, quantification, and differentiation between many of the Fusarium spp. associated with cereal and pulse crops.