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SNAREs (soluble N‐ethylmaleimide‐sensitive factor attachment protein receptors) facilitate docking and fusion of vesicles with their target membranes, playing a crucial role in vesicle trafficking and exocytosis. However, the spatial assembly and roles of plasma membrane (PM)‐associated SNAREs in phytopathogen development and pathogenicity are not clearly understood. In this study, we analysed the roles and molecular mechanisms of PM‐associated SNARE complexes in the banana Fusarium wilt fungus Fusarium oxysporum f. sp. cubense tropical race 4 (FocTR4). Our findings demonstrate that FocSso1 is important for the fungal growth, conidiation, host penetration and colonization. Mechanistically, FocSso1 regulates protein secretion by mediating vesicle docking and fusion with the PM and hyphal apex. Interestingly, a FocSso1–FocSec9–FocSnc1 complex was observed to assemble not only at the fungal PM but also on the growing hyphal apex, facilitating exocytosis. FocSso2, a paralogue of FocSso1, was also found to form a ternary SNARE complex with FocSec9 and FocSnc1, but it mainly localizes to the PM in old hyphae. The functional analysis of this protein demonstrated that it is dispensable for the fungal growth but necessary for host penetration and colonization. The other subunits, FocSec9 and FocSnc1, are involved in the fungal development and facilitate host penetration. Furthermore, FocSso1 and FocSnc1 are functionally interdependent, as loss of FocSso1 leads to mis‐sorting and degradation of FocSnc1 in the vacuole and vice versa. Overall, this study provides insight into the formation of two spatially and functionally distinct PM SNARE complexes and their involvement in vesicle exocytosis to regulate development and pathogenicity of FocTR4. Two SNARE complexes Sso1–Sec9–Snc1 and Sso2–Sec9–Snc1 were identified in Fusarium oxysporum f. sp. cubense that coordinately facilitate docking and fusion of exocytic vesicles with the plasma membrane in a spatially specific way.

Fusarium wilt of banana (also known as Panama disease) has been a problem in Australia since 1874. Race 1 of the pathogen (Fusarium oxysporum f.sp. cubense) is responsible for damage to Lady Finger (AAB, Pome subgroup) and other less widely grown cultivars such as Ducasse (Pisang Awak, ABB). Subtropical Race 4 (STR4) also affects these varieties as well as Cavendish (AAA) in southern Queensland and northern New South Wales where cold temperature predisposition is involved. Tropical Race 4 (TR4) has led to the demise of the Cavendish industry in the Northern Territory, and its presence was confirmed in a north Queensland plantation in 2015, which warranted destruction of all banana plants on the property; as of this writing (April 2019), TR4 has spread to two adjacent properties.

Most commercial banana cultivars are highly susceptible to Fusarium wilt caused by soilborne fungus Fusarium oxysporum f. sp. cubense (Foc), especially tropical race 4 (TR4). Biological control using antagonistic microorganism has been considered as an alternative method to fungicide. Our previous study showed that Streptomyces sp. SCA3-4  T had a broad-spectrum antifungal activity from the rhizosphere soil of Opuntia stricta in a dry hot valley. Here, the sequenced genome of strain SCA3-4  T contained 6614 predicted genes with 72.38% of G + C content. A polymorphic tree was constructed using the multilocus sequence analysis (MLSA) of five house-keeping gene alleles ( atpD , gyrB , recA , rpoB , and trpB ). Strain SCA3-4  T formed a distinct clade with Streptomyces mobaraensis NBRC 13819  T with 71% of bootstrap. Average nucleotide identity (ANI) values between genomes of strain SCA3-4  T and S. mobaraensis NBRC 13819  T was 85.83% below 95–96% of the novel species threshold, and named after Streptomyces sichuanensis sp. nov. The type strain is SCA3-4  T (= GDMCC 4.214  T  = JCM 34964  T ). Genomic analysis revealed that strain SCA3-4  T contained 36 known biosynthetic gene clusters of secondary metabolites. Antifungal activity of strain SCA3-4  T was closely associated with the production of siderophore and its extracts induced the apoptosis of Foc TR4 cells. A total of 12 potential antifungal metabolites including terpenoids, esters, acid, macrolides etc. were obtained by the gas chromatography-mass spectrometry (GC–MS). Greenhouse experiment indicated that strain SCA3-4  T could significantly inhibit infection of Foc TR4 in the roots and corms of banana seedlings and reduce disease index. Therefore, strain SCA3-4  T is an important microbial resource for exploring novel natural compounds and developing biopesticides to manage Foc TR4. Key points • Strain SCA3-4  T was identified as a novel species of Streptomyces. • Siderophore participates in the antifungal regulation. • Secondary metabolites of strain SCA3-4  T improves the plant resistance to Foc TR4.

Aims Banana Fusarium wilt ( Fusarium oxysporum f. sp. cubense tropical race 4) is a typical destructive soil-borne disease, which was the main limiting factor for the sustainable development of the banana industry worldwide. In banana production, soil physiochemical properties and soil microbiome were effectively affected the occurrence and spread of Fusarium wilt. However, there is still a lack of systematic research, particularly in exploring the correlation between the occurrence of banana Fusarium wilt and soil properties across various climates and soil types. Methods In this study we investigated the soil physicochemical properties, bacterial and fungal community composition, and pathogenic fungal abundance in 140 banana plantations which were affected by banana Fusarium wilt in Yunnan Province, China. Results The results showed that the abundance of soil-borne pathogenic fungi was positively correlated with total phosphorus, total nitrogen, organic matter, urease activity, annual precipitation, and the alpha diversity of bacterial and fungal communities. In contrast, it showed a significant negative correlation with the annual mean temperature. As the abundance of pathogen increased, numerous potential disease-suppressive bacterial genera (such as Rhodanobacter, Gemmatimonas, Novosphingobium) and soil-borne pathogenic fungal genera (such as Plectosphaerella, Nigrospora, Cyphellophora) also increased, and the co-occurrence network showed a higher modularization index. Conclusions The results enhance the understanding of the patterns of soil-borne pathogenic fungal population dynamics in banana plantations, which would provide evidence and guidance for reducing pathogenic fungal abundance and selecting beneficial microorganisms in banana production. Furthermore, this would provide a theoretical basis for sustainable prevention and control of banana wilt disease.

Background Banana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense is a soil-borne fungal disease. Especially, tropical Race 4 ( Foc TR4) can infect almost Cavendish subgroup and has a fatal threat to banana industry. Use of antagonistic microbes to manage soil-borne pathogen is viewed as a promising strategy. Results Strain XZ11-1 isolated from tropical rainforest has the production ability of high siderophore. By the analysis of physiological and biochemical profiles, construction of phylogenetic tree, and comparative results from the NR database, strain XZ11-1 was identified as Trichoderma virens . A relative content of 79.45% siderophores was produced in the optimized fermentation solution, including hydroxamate and carboxylate-type siderophores. Siderophores were key for inhibiting the growth of Foc TR4 by competing for environmental iron. Similarly, T. virens XZ11-1 also had antagonistic activities against 10 phytopathogenic fungi. Pot experiments demonstrated that T. virens XZ11-1 could colonize in the root system of banana plants. The symbiotic interaction not only improve plant resistance to Foc TR4, but also enhance iron absorption of roots to promote plant growth by secreting siderophores. Conclusions T. virens XZ11-1 with the high-yield siderophores was isolated and identified. The strain could effectively inhibit the infection of Foc TR4 in banana roots and promote plant growth. It is a promising biocontrol agent for controlling fungal disease.

The continuous cropping of banana in the same field may result in a serious soil-borne Fusarium wilt disease and a severe yield decline, a phenomenon known as soil sickness. Although soil microorganisms play key roles in maintaining soil health, the alternations of soil microbial community and relationship between these changes and soil sickness under banana monoculture are still unclear. Bacterial and fungal communities in the soil samples collected from banana fields with different monoculture spans were profiled by sequencing of the 16S rRNA genes and internal transcribed spacer using the MiSeq platform to explore the relationship between banana monoculture and Fusarium wilt disease in the present study. The results showed that successive cropping of banana was significantly correlated with the Fusarium wilt disease incidence. Fungal communities responded more obviously and quickly to banana consecutive monoculture than bacterial community. Moreover, a higher fungal richness significantly correlated to a higher banana Fusarium wilt disease incidence but a lower yield. Banana fungal pathogenic genus of Fusarium and Phyllosticta were closely associated with banana yield depletion and disease aggravation. Potential biocontrol agents, such as Funneliformis, Mortierella, Flavobacterium, and Acidobacteria subgroups, exhibited a significant correlation to lower disease occurrence. Further networks analysis revealed that the number of functionally interrelated modules decreased, the composition shifted from bacteria-to fungi-dominated among these modules, and more resources-competitive interactions within networks were observed after banana long-term monoculture. Our results also showed that bacterial and fungal communities were mainly driven by soil organic matter. Overall, the findings indicated that the bacterial and fungal community structures altered significantly after banana long-term monoculture, and the fungal richness, abundance of Fusarium, interactions between and within bacteria and fungi in ecological networks, and soil organic matter were associated with banana soilborne Fusarium wilt disease.

Summary Bananas (Musa spp.) are a major fruit crop worldwide, with the Cavendish cultivar dominating the export industries, which are based primarily in the Americas and the Philippines. The sustainability of banana production in these, and other regions, is under threat from the fungal disease Fusarium wilt tropical race 4 (TR4) which kills Cavendish and many other banana cultivars. No effective TR4 control strategies exist, and no consumer‐acceptable TR4‐resistant Cavendish replacements are currently available. Previously, we identified four genetically modified (GM) TR4‐resistant Cavendish (cv. Grand Nain) banana lines (RGA2‐2, ‐3, ‐4, and ‐5), each transformed with the MamRGA2 resistance gene derived from a TR4‐resistant wild banana. Here, we provide a comprehensive agronomic evaluation of these lines and report the regulatory approval of the top‐performing line, RGA2‐4 (QCAV‐4), in Australia. After five crop cycles of field trialling, TR4 disease incidence reached 66% and 84% in the Grand Nain and Williams non‐GM controls, respectively, while GM lines showed a significantly reduced incidence ranging from 2% (QCAV‐4) to 36% (RGA2‐5). Agronomic comparisons between QCAV‐4 and non‐GM Grand Nain controls for bunch weight, yield and cycle time indicated that, for most crop cycles, there were no differences, showing that, apart from TR4 resistance, QCAV‐4 is agronomically and phenotypically comparable to conventional Grand Nain. Molecular characterization of QCAV‐4 confirmed a single, large T‐DNA insert containing multiple copies of the MamRGA2 gene on chromosome 6 of the QCAV‐4 genome. QCAV‐4 is the first GM banana approved for commercial cultivation and consumption.

In our previous work, applying biofertilizer containing Bacillus amyloliquefaciens strain NJN-6 to a banana orchard infected by a serious Fusarium wilt disease over two consecutive years effectively controlled this soil-borne disease. In this study, deep pyrosequencing of 16S ribosomal RNA (rRNA) genes and internal transcribed spacer (ITS) sequences was performed to investigate how the composition of rhizosphere microbial community responded to the application of biofertilizer (BIO), pig manure compost (PM), and chemical fertilizer (CF) and to explore the potential correlation between the microbial community composition and the Fusarium wilt disease. A total of 104,201 bacterial 16S rRNA genes and 154,953 fungal ITS sequence reads were obtained after basic quality control, and Acidobacteria, Actinobacteria, Bacteroidetes, Firmicutes, Proteobacteria, and Ascomycota were the most abundant bacterial and fungal phyla across all samples. Compared with the PM and CF control, the alpha diversity of bacteria significantly (P < 0.05) increased, whereas the value of the fungi was significantly (P < 0.05) reduced following two consecutive years of biofertilizer application. Moreover, the abundance of Acidobacteria (Gp1 and Gp3), Firmicutes, Leptosphaeria, and Phaeosphaeriopsis was significantly (P < 0.05) increased, while the abundance of Proteobacteria and Ascomycota was significantly (P < 0.05) decreased in the BIO treatment. Furthermore, the abundance of Fusarium, a causal pathogen for Fusarium wilt disease, was significantly (P < 0.05) reduced in the BIO treatment compared with the CF control and was slightly reduced (not significant) compared with the PM control. Interestingly, the disease incidence was negatively correlated with the enriched taxa of Acidobacteria (Gp1 and Gp3) and Firmicutes, Leptosphaeria, and Phaeosphaeriopsis but positively correlated with abundance of Proteobacteria, Ascomycota, Fusarium, Cylindrocarpon, Gymnascella, Monographella, Pochonia, and Sakaguchia taxa. The results from this study suggest that 2 years of biofertilizer application manipulated the composition of rhizosphere microbial community and induced the Fusarium suppression by increasing bacterial diversity and potentially stimulating microbial consortia taxa, such as Acidobacteria (Gp1 and Gp3), Firmicutes, Leptosphaeria, and Phaeosphaeriopsis.

Fusarium wilt, caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc), is regarded as one of the most devastating diseases of bananas globally. Foc consists of three races, of which Foc races 1 and 2 occur in India. Foc race 4 has not been found in the country despite the importance and extensive cultivation of Cavendish cultivars. In 2015, a banana grower from Barari village in the Bihar State of India reported the wilting of Cavendish banana cvs. Robusta and Grand Naine. The incidence of the disease ranged from 2 to 26.6%. Symptoms included yellowing and browning of older leaves, which progressed from the oldest to the youngest leaves. Samples were collected from pseudostems and the responsible fungus isolated. The cultures were then identified using fungal morphology, vegetative compatibility group (VCG) analysis, volatile production and PCR with Foc tropical race (TR) 4-specific primers. Pathogenicity tests were conducted using Grand Naine plantlets produced by micropropagation. The cultures were identified as volatile-producing F. oxysporum strains, and pathogenicity tests confirmed their status as the banana pathogen Foc. VCG analysis, and the use of race-specific PCR markers, identified them as members of VCG 01213/16 and Foc TR4, respectively. This indicated that the fungus responsible for Fusarium wilt in the Bihar state of India is Foc TR4. Most Indian farmers use suckers as planting material, and are not aware of the impact of the disease. If the disease spreads to other states in India it can lead to an unemployment problem for farm labourers and the change in production to non-remunerative crops that may reduce profits.

Banana ( Musa spp.) is a staple food for more than 400 million people. Over 40% of world production and virtually all the export trade is based on Cavendish banana. However, Cavendish banana is under threat from a virulent fungus, Fusarium oxysporum f. sp. cubense tropical race 4 (TR4) for which no acceptable resistant replacement has been identified. Here we report the identification of transgenic Cavendish with resistance to TR4. In our 3-year field trial, two lines of transgenic Cavendish, one transformed with RGA2 , a gene isolated from a TR4-resistant diploid banana, and the other with a nematode-derived gene, Ced9 , remain disease free. Transgene expression in the RGA2 lines is strongly correlated with resistance. Endogenous RGA2 homologs are also present in Cavendish but are expressed tenfold lower than that in our most resistant transgenic line. The expression of these homologs can potentially be elevated through gene editing, to provide non-transgenic resistance. The newly recognized Fusarium wilt pathogen tropical race 4 is threatening worldwide banana production. Here, the authors transform Cavendish bananas with a resistance gene, RGA2 , from diploid banana or a nematode-derived gene, Ced9 , and confer resistance to natural infection under field conditions.