Tropical Race Research Articles

The Dual Effect of Selenium Application in Reducing Fusarium Wilt Disease Incidence in Banana and Producing Se-Enriched Fruits

Fusarium wilt disease severely constrains the global banana industry. The highly destructive disease is caused by Fusarium oxysporum f. sp. cubense, especially its virulent tropical race 4 (Foc TR4). Selenium (Se), a non-essential mineral nutrient in higher plants, is known to enhance plant resistance against several fungal pathogens. The experiments we conducted showed that selenium (≥10 mg/L) dramatically inhibited the growth of Foc TR4 mycelia and promoted plant growth. The further study we performed recorded a substantial reduction in the disease index (DI) of banana plants suffering from Foc TR4 when treated with selenium. The selenium treatments (20~160 mg/L) demonstrated significant control levels, with recorded symptom reductions ranging from 42.4% to 65.7% in both greenhouse and field trials. The DI was significantly negatively correlated with the total selenium content (TSe) in roots. Furthermore, selenium treatments enhanced the antioxidant enzyme activities of peroxidase (POD), polyphenol oxidase (PPO), and glutathione peroxidase (GSH-Px) in banana. After two applications of selenium (100 and 200 mg/plant) in the field, the TSe in banana pulps increased 23.7 to 25.9-fold and achieved the Se enrichment standard for food. The results demonstrate that selenium applications can safely augment root TSe levels, both reducing Fusarium wilt disease incidence and producing Se-enriched banana fruits. For the first time, this study has revealed that selenium can significantly reduce the damage caused by soil-borne pathogens in banana by increasing the activities of antioxidant enzymes and inhibiting fungal growth.

Specific PCR primer designed from genome data for rapid detection of Fusarium oxysporum f. sp. cubense tropical race 4 in the Cavendish banana.

Fusarium wilt caused by Fusarium oxysporum f. sp. cubense (Foc) tropical race 4 (TR4) severely affects banana production worldwide. Thus, specific PCR primers have been developed to rapidly diagnose and monitor Foc TR4-related fusarium wilt outbreaks in bananas. However, evaluation of these primers revealed room for improvement in the accuracy. This study aimed to design highly specific PCR primers based on genome data for Foc TR4 downloaded from the National Center for Biotechnology Information database. The specificity of the primers was assessed using Foc TR4, Foc races 1 and 2, and 15 other formae speciales strains. The utility of the primers was verified by correctly detecting Foc TR4 in 7 out of 86 isolates of Fusarium spp. obtained from banana farms in the Philippines. The primers allowed for rapid detection in experimentally diseased tissues. We concluded that this novel primer set enables the simplified diagnosis of fusarium wilt caused by Foc TR4 in bananas.

Histological Dissection of Fusarium-Banana Interaction Using a GFP-Tagged Subtropical Race 4 Strain of Fusarium oxysporum f. sp. cubense on Banana Cultivars with Differing Levels of Resistance

Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (Foc), poses a significant threat to global banana production. This study used a GFP-tagged subtropical race 4 strain of Foc (GFP-Foc-STR4) to trace the pathogen’s movement in different banana cultivars. These include a race 4 resistant cultivar FHIA25 and the Cavendish somaclone ‘GCTCV119’, as well as susceptible cultivars including ‘Lady Finger’, ‘FHIA02’, and ‘Williams’ Cavendish. GFP localization revealed that GFP-Foc-STR4 was able to infect all tested cultivars, moving from the roots to the rhizome and aerial parts of the plant. Tyloses formation in root and rhizome vasculature, visualised with GFP autofluorescence and confirmed by scanning electron microscopy, was found to restrict Foc within the xylem vessels, slowing its spread but not fully preventing infection. This containment mechanism contributes to the host tolerance of ‘FHIA25’ and ‘GCTCV119’, though it does not confer complete immunity. The use of the fluorescently tagged Foc strain provides valuable insight into the infection process, and supports efforts in the integrated management of Fusarium wilt of banana.

Integrated Transcriptome and sRNAome Analysis Reveals the Molecular Mechanisms of Piriformospora indica-Mediated Resistance to Fusarium Wilt in Banana.

Bananas (Musa spp.) are among the most important fruit and staple food crops globally, holding a significant strategic position in food security in tropical and subtropical regions. However, the industry is grappling with a significant threat from Fusarium wilt, a disease incited by Fusarium oxysporum f. sp. cubense (Foc). In this study, we explored the potential of Piriformospora indica (Pi), a mycorrhizal fungus renowned for bolstering plant resilience and nutrient assimilation, to fortify bananas against this devastating disease. Through a meticulous comparative analysis of mRNA and miRNA expression in control, Foc-inoculated, Pi-colonized, and Pi-colonized followed by Foc-inoculated plants via transcriptome and sRNAome, we uncovered a significant enrichment of differentially expressed genes (DEGs) and DE miRNAs in pathways associated with plant growth and development, glutathione metabolism, and stress response. Our findings suggest that P. indica plays a pivotal role in bolstering banana resistance to Foc. We propose that P. indica modulates the expression of key genes, such as glutathione S-transferase (GST), and transcription factors (TFs), including TCP, through miRNAs, thus augmenting the plant's defensive capabilities. This study offers novel perspectives on harnessing P. indica for the management of banana wilt disease.

Biocontrol Agents Inhibit Banana Fusarium Wilt and Alter the Rooted Soil Bacterial Community in the Field.

Banana is an important fruit and food crop in tropical and subtropical regions worldwide. Banana production is seriously threatened by Fusarium wilt of banana (FWB), a disease caused by Fusarium oxysporum f. sp. cubense, and biological control is an important means of curbing this soil-borne disease. To reveal the effects of biocontrol agents on inhibiting FWB and altering the soil bacterial community under natural ecosystems, we conducted experiments at a banana plantation. The control efficiency of a compound microbial agent (CM), Paenibacillus polymyxa (PP), Trichoderma harzianum (TH), and carbendazim (CA) on this disease were compared in the field. Meanwhile, the alterations in structure and function of the rooted soil bacterial community in different treatments during the vigorous growth and fruit development stages of banana were analyzed by microbiomics method. The results confirmed that the different biocontrol agents could effectively control FWB. In particular, CM significantly reduced the incidence of the disease and showed a field control efficiency of 60.53%. In terms of bacterial community, there were no significant differences in the richness and diversity of banana rooted soil bacteria among the different treatments at either growth stage, but their relative abundances differed substantially. CM treatment significantly increased the ratios of Bacillus, Bryobacter, Pseudomonas, Jatrophihabitans, Hathewaya, and Chujaibacter in the vigorous growth stage and Jatrophihabitans, Occallatibacter, Cupriavidus, and 1921-3 in the fruit development stage. Furthermore, bacterial community function in the banana rooted soil was affected differently by the various biocontrol agents. CM application increased the relative abundance of multiple soil bacterial functions, including carbohydrate metabolism, xenobiotic biodegradation and metabolism, terpenoid and polyketide metabolism, lipid metabolism, and metabolism of other amino acids. In summary, our results suggest that the tested biocontrol agents can effectively inhibit the occurrence of banana Fusarium wilt and alter the soil bacterial community in the field. They mainly modified the relative abundance of bacterial taxa and the metabolic functions rather than the richness and diversity. These findings provide a scientific basis for the use of biocontrol agents to control banana Fusarium wilt under field conditions, which serves as a reference for the study of the soil microbiological mechanisms of other biocontrol agents.

Integrated control of Fusarium wilt in banana by Bacillus velezensis EB1 and potassium sorbate

Fusarium wilt of banana, caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), is a widely distributed soilborne disease that poses a serious threat to banana production. Many control measures have been implemented but have not been effective. Here, we evaluated a combined strategy for Fusarium wilt control that involves a biological agent (Bacillus velezensis strain EB1) and a bioactive compound (potassium sorbate). Our results showed that potassium sorbate inhibited Foc TR4 in a dose-dependent manner. Potassium sorbate did not limit the growth of EB1 in vitro; instead, it promoted the growth and antagonistic ability of EB1 by upregulating the expression of antagonism-related genes. In greenhouse experiments, the combined application of EB1 and potassium sorbate significantly reduced the disease index of Fusarium wilt by suppressing fungal growth in the roots and promoting plant growth. Overall, our results demonstrated that potassium sorbate and B. velezensis EB1 can be used together for the sustainable management of banana Fusarium wilt.

The importin FocKap119 is required for fungal growth and pathogenicity of the Fusarium oxysporum f. sp. cubense via interaction with FocCks1

Fusarium oxysporum f. sp. cubense (Foc), the causal agent of banana wilt disease, is one of the most devastating pathogens of bananas (Musa spp.). The nucleocytoplasmic trafficking of proteins and RNAs, mediated by karyopherins (Kaps), is essential for eukaryotes. However, little is known about how Kaps regulate fungal growth and pathogenicity. Here, a Kap119 homolog (FocKap119) was identified in the Foc tropical race 4 strain Foc302. Deletion of FocKap119 led to impaired vegetative growth, conidiation, cell wall integrity, and pathogenicity. Compared to the wild type, the ΔFocKap119 mutant showed increased sensitivity to oxidative stress but greater tolerant to osmotic stress. FocKap119 was found to interact with FocCks1 (cell cycle-dependent kinase subunit 1) in a yeast two-hybrid system, and deletion of FocCks1 showed similar phenotypes as ΔFocKap119. Moreover, whole-transcriptome analysis and qRT-PCR results indicated that deletion of FocKap119 resulted in down-regulation of genes related to key virulence factor biosynthesis, including fusaric acid and beauvericin biosynthetic gene clusters. The ΔFocKap119 mutant also triggered stronger plant defense responses during the early infection compared to the wild type. This study provides insights into how FocKap119 regulated growth, abiotic stress response, and pathogenicity in Foc.

A socioeconomic and cost benefit analysis of Tropical Race 4 (TR4) prevention methods among banana producers in Colombia.

The global banana industry faces a significant threat from Fusarium oxysporum f. sp. cubense Tropical Race 4 (TR4). While prior research has concentrated on TR4's dissemination, reproductive conditions, and resistant banana varieties, this study employs a socioeconomic and cost-benefit analysis to explore the vulnerability of banana producers to TR4 in Colombia. It assesses the financial viability of current monitoring strategies and estimates potential losses in the event of TR4 spreading within the study area. Interviews were conducted with producers and key stakeholders in Colombia's top two banana-producing departments, Antioquia and Magdalena. The findings reveal that farming systems are highly vulnerable to TR4, particularly due to the prevalent use of corms. Producers employ preventive measures such as cement paths, fences, disinfecting stations, and footbaths to counteract TR4's spread. A cost-benefit analysis indicates that the benefits of these prevention methods significantly outweigh the associated costs, with a net present value of implementing prevention strategies per hectare of $95,389 USD and $112,527 USD in Magdalena and Antioquia and a benefit-cost ratio of 3.1 and 4.2, respectively. Considering the substantial impact TR4 could have in Colombia if it becomes more widespread, we recommend widespread adoption of preventive measures, including the construction and utilization of cement paths and disinfectant methods on all banana farms. Additionally, to enhance awareness and early detection, we propose leveraging technology, such as mobile applications (apps) and chat groups, to empower farmers in identifying and preventing the spread of TR4.

In silico profiling, docking analysis, and protein interactions of secondary metabolites in Musa spp. Against the SGE1 protein of Fusarium oxysporum f. sp. cubense

Banana Fusarium Wilt (BFW), caused by Fusarium oxysporum f. sp. cubense (Foc), threatens banana crops globally, with the pathogen's virulence partially regulated by the Sge1 transcription factor, which enhances disease severity. Certain Musa species display resistance to Foc, suggesting inherent genetic traits that confer immunity against Sge1Foc. This study utilized bioinformatics tools to investigate the mechanisms underlying this resistance in Musa accuminata subsp. aalaccensis. Through in silico analyses, we explored interactions between Musa spp. and Foc, focusing on the Sge1 protein. Tools such as Anti-SMASH, AutoDockVina 4.0, STRING, and Phoenix facilitated the profiling of secondary metabolites in Musa spp. and the identification of biosynthetic gene clusters involved in defense. Our results indicate that secondary metabolites, including saccharides, terpenes, and polyketides, are crucial to the plant's immune response. Molecular docking studies of selected Musa metabolites, such as 3-Phenylphenol, Catechin, and Epicatechin, revealed 3-Phenylphenol as having the highest binding affinity to the Sge1Foc protein (-6.7 kcal/mol).Further analysis of gene clusters associated with secondary metabolite biosynthesis in Musa spp. identified key domains like Chalcone synthase, Phenylalanine ammonia-lyase, Aminotran 1–2, and CoA-ligase, which are integral to phenylpropanoid production—a critical pathway for secondary metabolites. The study highlights that the phenylpropanoid pathway and secondary metabolite biosynthesis are vital for Musa spp. resistance to Foc. Flavonoids and lignin may inhibit Sge1 protein formation, potentially disrupting Foc's cellular processes. These findings emphasize the role of phenylpropanoid pathways and secondary metabolites in combating BFW and suggest that targeting these pathways could offer innovative strategies for enhancing resistance and controlling BFW in banana crops. This research lays the groundwork for developing sustainable methods to protect banana cultivation and ensure food security.

A virulent milRNA inhibits host immunity by silencing a host receptor-like kinase MaLYK3 and facilitates infection by Fusarium oxysporum f. sp. cubense.

MicroRNA-like RNAs (milRNAs) play a significant role in the infection process by plant-pathogenic fungi. However, the specific functions and regulatory mechanisms of fungal milRNAs remain insufficiently elucidated. This study investigated the function of Foc-milR138, an infection-induced milRNA secreted by Fusarium oxysporum f. sp. cubense (Foc), which is the causal agent of Fusarium wilt of banana. Initially, through precursor gene knockout and phenotypic assessments, we confirmed that Foc-milR138 acts as a virulent milRNA prominently upregulated during the early stages of Foc infection. Subsequent bioinformatic analyses and transient expression assays in Nicotiana benthamiana leaves identified a host receptor-like kinase gene, MaLYK3, as the direct target of Foc-milR138. Functional investigations of MaLYK3 revealed its pivotal role in triggering immune responses of N. benthamiana by upregulating a suite of resistance genes, bolstering reactive oxygen species (ROS) accumulation and callose deposition, thereby fortifying disease resistance. This response was markedly subdued upon co-expression with Foc-milR138. Expression pattern analysis further verified the specific suppression of MaLYK3 by Foc-milR138 during the early root infection by Foc. In conclusion, Foc secretes a virulent milRNA (Foc-milR138) to enter the host banana cells and inhibit the expression of the plant surface receptor-like kinase MaLYK3, subverting the disease resistance activated by MaLYK3, and ultimately facilitating pathogen invasion. These findings shed light on the roles of fungal milRNAs and their targets in resistance and pathogenicity, offering promising avenues for the development of disease-resistant banana cultivars.

Antimicrobial mechanisms and antifungal activity of compounds generated by banana rhizosphere Pseudomonas aeruginosa Gxun-2 against fusarium oxysporum f. sp. cubense.

Fusarium wilt of banana, also recognized as Panama disease, is caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense tropical race 4 (FOC TR4). In recent years, strategies utilizing biocontrol agents, comprising antifungal microorganisms and their associated bioactive compounds from various environments, have been implemented to control this destructive disease. Our previous study showed that Pseudomonas aeruginosa Gxun-2 had significant antifungal effects against FOC TR4. However, there has been little scientific investigation of the antibacterial or antifungal activity. The aim of this study was to isolate, identify and evaluate the inhibition strength of active compounds in P. aeruginosa Gxun-2, so as to explain the mechanism of the strain inhibition on FOC TR4 from the perspective of compounds. The main antibacterial compounds of strain Gxun-2 were isolated, purified and identified using by fermentation extraction, silica gel column chromatography, thin-layer chromatography (TLC), high-performance liquid chromatography (HPLC), and nuclear magnetic resonance (NMR) techniques. The effect of the compounds on the mycelial growth, morphology and spore germination of strain FOC TR4 was observed by 96-well plate method and AGAR diffusion method. Among the metabolites produced by the strain, four antifungal compounds which were identified phenazine (C12H8N2), phenazine-1-carboxylic acid (PCA) (C13H8N2O2), 2-acetamidophenol (C8H9NO2) and aeruginaldehyde (C10H7NO2S) were identified through HPLC and NMR. Of these compounds, phenazine and PCA exhibited the most pronounced inhibitory effects on the spore germination and mycelial growth of FOC TR4. Phenazine demonstrated potent antifungal activity against FOC TR4 with a minimum inhibitory concentration (MIC) of 6.25 mg/L. The half-maximal effective concentration (EC50) was calculated to be 26.24 mg/L using the toxicity regression equation. PCA exhibited antifungal activity against FOC TR4 with an MIC of 25 mg/L and an EC50 of 89.63 mg/L. Furthermore, phenazine and PCA triggered substantial morphological transformations in the mycelia of FOC TR4, encompassing folding, bending, fracturing, and diminished spore formation. These findings indicate that strain Gxun-2 plays a crucial role in controlling FOC TR4 pathogenesis, predominantly through producing the antifungal compounds phenazine and PCA, and possesses potential as a cost-efficient and sustainable biocontrol agent against Fusarium wilt of banana in forthcoming times.

Tropical Race 4 and Race 1 strains causing Fusarium wilt of banana infect and survive in Heliconia species and ornamental bananas

Tropical Race 4 and Race 1 strains causing Fusarium wilt of banana infect and survive in Heliconia species and ornamental bananas

Spatiotemporal dynamics of Fusarium wilt of banana caused by Subtropical Race 4

Spatiotemporal dynamics of Fusarium wilt of banana caused by Subtropical Race 4

The complete mitochondrial genome of the banana pathogen Fusarium oxysporum f. sp. cubense M5.

We report the complete mitochondrial genome of a causal agent of banana fusarium wilt isolated in Mexico. The whole set of genes encoding proteins related to respiration and ATP synthesis, rRNAs, tRNAs are enlisted. Two open reading frames of unknown function conserved in Fusarium oxysporum were also identified.

The occurrence of banana Fusarium wilt aggravates antibiotic resistance genes dissemination in soil

The spread of antibiotic resistance genes (ARGs) and subsequent soil-borne disease outbreaks are major threats to soil health and sustainable crop production. However, the relationship between occurrences of soil-borne diseases and the transmission of soil ARGs remains unclear. Here, soil ARGs, mobile genetic elements and microbial communities from co-located disease suppressive and conducive banana orchards were deciphered using metagenomics and metatranscriptomics approaches. In total, 23 ARG types, with 399 subtypes, were detected using a metagenomics approach, whereas 23 ARG types, with 452 subtypes, were discovered using a metatranscriptomics method. Furthermore, the metagenomics analysis revealed that the ARG total abundance levels were greater in rhizospheres (0.45 ARGs/16S rRNA on average) compared with bulk (0.32 ARGs/16S rRNA on average) soils. Interestingly, metatranscriptomics revealed that the total ARG abundances were greater in disease-conducive (8.85 ARGs/16S rRNA on average) soils than disease suppressive (1.45 ARGs/16S rRNA on average) soils. Mobile genetic elements showed the same trends as ARGs. Network and binning analyses indicated that Mycobacterium, Streptomyces, and Blastomonas are the main potential hosts of ARGs. Furthermore, Bacillus was significantly and negatively correlated with Fusarium (P < 0.05, r = −0.84) and hosts of ARGs (i.e., Mycobacterium, Streptomyces, and Blastomonas). By comparing metagenomic and metatranscriptomic analyses，this study demonstrated that metatranscriptomics may be more sensitive in indicating ARGs activities in soil. Our findings enable the more accurate assessment of the transmission risk of ARGs. The data provide a new perspective for recognizing soil health, in which soil-borne disease outbreaks appear to be associated with ARG spread, whereas beneficial microbe enrichment may mitigate wilt disease and ARG transmission.

Combining cyclic lipopeptides and cinnamon extract enhance antifungal activity against Fusarium oxysporum strains pathogenic to banana and delay Fusarium wilt under greenhouse conditions

Fusarium wilt of banana (FWB) caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc) is a widely distributed disease that generates devastating losses in banana production. Foc belongs to the Fusarium oxysporum species complex (FOSC) which includes several evolutionary lineages. Nine of them are pathogenic to banana such as F. phialophorum, F. grosmichelli, F. duoseptatum and the most aggressive F. odoratissimum tropical race 4 (TR4). No control method has been successfully implemented to manage FWB, then enhancing the potential of management approaches can avoid or delay disease epidemics and reduce disease severity. Here we determined the antifungal effect of different plant-based extracts against Foc in vitro, and whether the combination of cinnamon (Cinnamomum zeylanicum) extract and Bacillus tequilensis EA-CB0015 cyclic lipopeptides had an additive effect against different Foc lineages in vitro and against FWB in banana plants in greenhouse. We found, from 17 plant-based natural extracts, that cinnamon was highly active against Foc strain IB (race 1). Furthermore, cinnamon and cyclic lipopeptides inhibited different strains of various evolutionary lineages of Foc belonging to race 1 and TR4, and their combination increased in 1.4-fold the effect of the single extracts in vitro. Our results showed that soil concentration of F. odoratissimum TR4-II5 decreased by 1000-fold when treated with the combination of 488 mg L−1 cinnamon and 128 mg L−1 lipopeptides in a soil microcosm system after 5 days of incubation, followed by a partial population recovery after 21 days. In greenhouse experiments, the combination reduced external but not internal FWB symptoms, and cinnamon extract had a significant impact on internal plant symptoms. Taken together, the effect of cyclic lipopeptides with cinnamon extract on Foc supports their function towards delaying the effect of disease progression and suggests that the combination enhances the effect of the single extracts.

Antarctic Streptomyces: Promising biocontrol agents for combating Fusarium oxysporum f. sp. cubense

Fusarium wilt of Banana (FWB) caused by Fusarium oxysporum f. sp. cubense (Foc) poses a significant threat to the banana industry, with current inadequate control measures. This study evaluated the antifungal potential of nine Streptomyces strains isolated from Antarctic soil samples, using Casein-Starch media to stimulate the production of antifungal compounds. The inhibition spectrum against Foc was assessed under laboratory conditions using the well diffusion on Mueller-Hinton agar, with antifungal activity measured in arbitrary units (AU/mL) and minimum inhibitory concentration (MIC) tested using ethyl acetate extracts. Among the nine isolates, K6 and E7 were closely related to Streptomyces polyrhachis and Streptomyces fildesensis, exhibited significant antifungal activity, with K6 and E7 showing 320 and 80 AU/mL, and MIC values of 250 and >500 ppm, respectively. These findings highlight K6 and E7 as potential biocontrol agents against Foc, offering new avenues for sustainable Fusarium wilt management in banana cultivation.

Virulence of banana wilt-causing fungal pathogen Fusarium oxysporum tropical race 4 is mediated by nitric oxide biosynthesis and accessory genes.

Fusarium wilt of banana, caused by Fusarium oxysporum f. sp. cubense (Foc), is one of the most damaging plant diseases known. Foc race 1 (R1) decimated the Gros Michel-based banana (Musa acuminata) trade, and now Foc tropical race 4 (TR4) threatens global production of its replacement, the Cavendish banana. Here population genomics revealed that all Cavendish banana-infecting Foc race 4 strains share an evolutionary origin distinct from that of R1 strains. Although TR4 lacks accessory chromosomes, it contains accessory genes at the ends of some core chromosomes that are enriched for virulence and mitochondria-related functions. Meta-transcriptomics revealed the unique induction of the entire mitochondrion-localized nitric oxide (NO) biosynthesis pathway upon TR4 infection. Empirically, we confirmed the unique induction of a NO burst in TR4, suggesting that nitrosative pressure may contribute to virulence. Targeted mutagenesis demonstrated the functional importance of fungal NO production and the accessory gene SIX4 as virulence factors.

A ribonuclease T2 protein FocRnt2 contributes to the virulence of Fusarium oxysporum f. sp. cubense tropical race 4.

Banana Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), is a major disease of banana plants worldwide. Effector proteins play critical roles in banana-Foc TR4 interaction. Our previous studies highlighted a ribonuclease protein belonging to the T2 family (named as FocRnt2) in the Foc TR4 secretome, which was predicted to be an effector. However, its biological function in Foc TR4 infection is still unclear. Herein, we observed significant expression of FocRnt2 during the early stage of fungal infection in planta. A yeast signal sequence trap assay showed that FocRnt2 contained a functional signal peptide for secretion. FocRnt2 possessed ribonuclease activity that could degrade the banana total RNA invitro. Subcellular localization showed that FocRnt2 was localized in the nucleus and cytoplasm of Nicotiana benthamiana leaves. Transient expression of FocRnt2 suppressed the expression of salicylic acid- and jasmonic acid-signalling marker genes, reactive oxygen species accumulation, and BAX-mediated cell death in N. benthamiana. FocRnt2 deletion limited fungal penetration, reduced fusaric acid biosynthesis in Foc TR4, and attenuated fungal virulence against banana plants, but had little effect on Foc TR4 growth and sensitivity to various stresses. Furthermore, FocRnt2 deletion mutants induced higher expression of the defence-related genes in banana plants. These results suggest that FocRnt2 plays an important role in full virulence of Foc TR4, further improving our understanding of effector-mediated Foc TR4 pathogenesis.

Streptomyces-Secreted Fluvirucin B6 as a Potential Bio-Fungicide for Managing Banana Fusarium Wilt and Mycotoxins and Modulating the Soil Microbial Community Structure.

Banana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense (Foc TR4) is the most destructive soil-borne fungal disease. Until now, there has been a lack of effective measures to control the disease. It is urgent to explore biocontrol agents to control Foc TR4 and the secretion of mycotoxin. In this study, fluvirucin B6 was screened from Streptomyces solisilvae using an activity-guided method. Fluvirucin B6 exhibited strong antifungal activity against Foc TR4 (0.084 mM of EC50 value) and significantly inhibited mycelial growth and spore germination. Further studies demonstrated that fluvirucin B6 could cause the functional loss of mitochondria, the disorder of metabolism of Foc TR4 cells, and the decrease of enzyme activities in the tricarboxylic acid cycle and electron transport chain, ultimately inhibiting mycotoxin metabolism. In a pot experiment, the application of fluvirucin B6 significantly decreased the incidence of banana Fusarium wilt and the amount of Foc TR4 and controlled fungal toxins in the soil. Additionally, fluvirucin B6 could positively regulate the changes in the structure of the banana rhizosphere microbial community, significantly enriching beneficial microbes associated with disease resistance. In summary, this study identifies fluvirucin B6, which plays versatile roles in managing fungal diseases and mycotoxins.