Tropical Race Research Articles

Construction of a compound microbial agent for biocontrol against Fusarium wilt of banana.

Banana wilt caused by Fusarium oxysporum f. sp. cubense has devastated a large number of banana plantations worldwide. Biological control is a possible method to conquer this disease. However, the control effect was often low and unstable while a single biocontrol strain had been applied in the field. Therefore, this study aimed to construct an effective compound microbial agent to control Fusarium wilt of banana (FWB) in the field. In addition to it, the compounding strategy of combining single strains for improving the control effect was investigated. Based on the compatibility test, five representative biocontrol strains were selected for the combination of all possible permutations. The pot experiment indicated that every biocontrol strain and their 26 combinations could control FWB to varying degrees. The control effect of combinations on FWB was higher than that of a single strain. In terms of the number of combinatorial biocontrol strains, the control effect of the four-strain combinations was the highest. According to the taxonomic differences of the five biocontrol strains, 26 biocontrol strain combinations could be divided into four groups. Among the strains in the combination, the larger the taxonomic differences the more easily it was to obtain a higher control effect. To obtain stable and efficient combinations, eight combinations were selected out and evaluated for their effectiveness in controlling FWB in different type soil. Compared with the other seven combinations, the four-strain combination T28 (Pt05 + Bc11 + Ba62 + gz-2) got the highest and stablest control effect in the four types of soil in greenhouse. And then the control effect of combination T28 was evaluated in field conditions, compared with commercially agents Bacillus subtilis, Trichoderma harzianum, and carbendazim. After four consecutive applications in the field, the control effect of T28 against FWB was the highest, reaching 57.14%. The results showed that combination T28 had a good application prospect, and the finding provided a reference for the construction of compound microbial agents.

Fluorine-containing amphiphilic quaternary ammonium salts for the suppression of Banana fusarium wilt

As the pathogen of banana Fusarium wilt, Fusarium oxysporum f. sp. cubense race 4 (Foc4) has the strongest toxicity and pathogenicity due to its long-term viability in soil, but there is still no effective way to control it at present. Based on the activity parameters of polymeric quaternary ammonium salt in our previous work, this paper hopes to enhance the amphiphilicity of polymeric quaternary ammonium salt by introducing a fluoroalkyl group to improve the antifungal property of polymeric quaternary ammonium salt and achieve stable adsorption and long-term inhibition of saprophytic Foc4 conidia in soil. Here, we prepared a series of fluorine-containing ammonium salts with random and block structures by atom transfer radical polymerization (ATRP), and we systematically studied the effects of the introduction of fluoroalkyl groups, the proportion of hydrophobic segments and polymer structure on micelle properties, antifungal properties, adsorption, migration and long-term antifungal properties against Foc4 in soil. Finally, the preferred polymeric quaternary ammonium salts were selected for pot experiments in the prevention and control of banana Fusarium wilt caused by Foc4, and positive experimental results were achieved. In conclusion, we made an exploratory attempt at the practical application of polymeric amphiphilic quaternary ammonium salt in plant disease control.

Genome Sequence Data Reveal at Least Two Distinct Incursions of the Tropical Race 4 Variant of Fusarium Wilt into South America.

The global banana industry is threatened by one of the most devastating diseases: Fusarium wilt of banana. Fusarium wilt of banana is caused by the soilborne fungus Fusarium oxysporum f. sp. cubense (Foc), which almost annihilated the banana production in the late 1950s. A new strain of Foc, known as tropical race 4 (TR4), attacks a wide range of banana varieties, including Cavendish clones, which are the source of 99% of banana exports. In 2019, Foc TR4 was reported in Colombia, and more recently (2021) in Peru. In this study, we sequenced three fungal isolates identified as Foc TR4 from La Guajira (Colombia) and compared them against 19 whole-genome sequences of Foc TR4 publicly available, including four genome sequences recently released from Peru. To understand the genetic relatedness of the Colombian Foc TR4 isolates and those from Peru, we conducted a phylogenetic analysis based on a genome-wide set of single nucleotide polymorphisms (SNPs). Additionally, we compared the genomes of the 22 available Foc TR4 isolates, looking for the presence-absence of gene polymorphisms and genomic regions. Our results reveal that (i) the Colombian and Peruvian isolates are genetically distant, which could be better explained by independent incursions of the pathogen to the continent, and (ii) there is a high correspondence between the genetic relatedness and geographic origin of Foc TR4. The profile of present/absent genes and the distribution of missing genomic regions showed a high correspondence to the clades recovered in the phylogenetic analysis, supporting the results obtained by SNP-based phylogeny.

Survey, identification and management of Fusarium wilt of banana in Tamirabarani tract of Southern districts of Tamil Nadu

In Tamil Nadu state, Thoothukudi district ranked second in banana production and especially the Tamirabarani tract of Thoothukudi and Tirunelveli districts are known for the production of various banana cultivars like Rasthali, Andhra Kozhi, Karpooravalli, Neypoovan, Poovan, Peyan and Chakkai. Among these varieties, cultivation of Rasthali faces 50-60% yield loss due to the incidence of Fusarium wilt disease. As the farmers have been practising ratooning for 6-7 year continuously which enhances the inoculum load of the pathogen and make the plantains succumb to Fusarium oxysporum f. sp. cubense (Foc). Studies carried out on different treatments in the management of Fusarium wilt of banana, Trichoderma sp. Tsp1(ALG) showed a maximum reduction of mycelial growth of Foc (72.18%) over control which was on par with Pseudomonas fluorescence 1(Pf1). Under pot culture conditions the combination of three treatments, Tsp1(ALG)+Pf1+ neem cake excelled and showed an 80% reduction of wilt incidence. A multifaceted approach comprising the application of biocontrol agents (Trichoderma sp.) + Pseudomonas sp. 1 (TNAU) and organic amendments was found to be the best management practice in containing the wilt.

Antifungal Mechanism of Metabolites from Newly Isolated Streptomyces sp. Y1-14 against Banana Fusarium Wilt Disease Using Metabolomics.

Banana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) is one of the most destructive banana diseases in the world, which limits the development of the banana industry. Compared with traditional physical and chemical practices, biological control becomes a promising safe and efficient strategy. In this study, strain Y1-14 with strong antagonistic activity against Foc TR4 was isolated from the rhizosphere soil of a banana plantation, where no disease symptom was detected for more than ten years. The strain was identified as Streptomyces according to the morphological, physiological, and biochemical characteristics and the phylogenetic tree of 16S rRNA. Streptomyces sp. Y1-14 also showed a broad-spectrum antifungal activity against the selected 12 plant pathogenic fungi. Its extracts inhibited the growth and spore germination of Foc TR4 by destroying the integrity of the cell membrane and the ultrastructure of mycelia. Twenty-three compounds were identified by gas chromatography-mass spectrometry (GC-MS). The antifungal mechanism was investigated further by metabolomic analysis. Strain Y1-14 extracts significantly affect the carbohydrate metabolism pathway of Foc TR4 by disrupting energy metabolism.

Comparative Transcriptome Analysis Unravels the Response Mechanisms of Fusarium oxysporum f.sp. cubense to a Biocontrol Agent, Pseudomonas aeruginosa Gxun-2

Banana Fusarium wilt, which is caused by Fusarium oxysporum f.sp. cubense Tropical Race 4 (FOC TR4), is one of the most serious fungal diseases in the banana-producing regions in east Asia. Pseudomonas aeruginosa Gxun-2 could significantly inhibit the growth of FOC TR4. Strain Gxun-2 strongly inhibited the mycelial growth of FOC TR4 on dual culture plates and caused hyphal wrinkles, ruptures, and deformities on in vitro cultures. Banana seedlings under pot experiment treatment with Gxun-2 in a greenhouse resulted in an 84.21% reduction in the disease. Comparative transcriptome analysis was applied to reveal the response and resistance of FOC TR4 to Gxun-2 stress. The RNA-seq analysis of FOC TR4 during dual-culture with P. aeruginosa Gxun-2 revealed 3075 differentially expressed genes (DEGs) compared with the control. Among the genes, 1158 genes were up-regulated, and 1917 genes were down-regulated. Further analysis of gene function and the pathway of DEGs revealed that genes related to the cell membrane, cell wall formation, peroxidase, ABC transporter, and autophagy were up-regulated, while down-regulated DEGs were enriched in the sphingolipid metabolism and chitinase. These results indicated that FOC TR4 upregulates a large number of genes in order to maintain cell functions. The results of qRT-PCR conducted on a subset of 13 genes were consistent with the results of RNA-seq data. Thus, this study serves as a valuable resource regarding the mechanisms of fungal pathogen resistance to biocontrol agents.

Evaluation of Resistance of Banana Genotypes with AAB Genome to Fusarium Wilt Tropical Race 4 in China.

Banana cultivars with the AAB genome group comprise diverse subgroups, such as Plantain, Silk, Iholena, and Pisang Raja, among others, which play an important role in food security in many developing countries. Some of these cultivars are susceptible to Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4), the most destructive pathogen threatening banana production worldwide, and some of them are still largely unknown. We evaluated the resistance of 37 banana genotypes, including Plantain, Silk, Iholena, Maia Maoli/Popoulu, Pisang Raja, Pome, and Mysore, to Foc TR4 under both greenhouse and field conditions. Genotypes from the Silk and Iholena subgroups were highly susceptible to Foc TR4. Pome and Mysore showed resistance and intermediate resistance, respectively. However, Pisang Raja ranged from susceptible to intermediate resistance. One cultivar from the Maia Maoli/Popoulu subgroup was highly susceptible, while the other displayed significant resistance. Most Plantain cultivars exhibited high resistance to Foc TR4, except two French types of cultivar, 'Uganda Plantain' and 'Njombe N°2', which were susceptible. The susceptibility to Foc TR4 of some of the AAB genotypes evaluated, especially Plantain and other cooking bananas, indicates that growers dependent on these varieties need to be included as part of the prevention and integrated Foc TR4 management strategies, as these genotypes play a crucial role in food security and livelihoods.

First Report of Fusarium Wilt of Iholena Banana (Musa spp.) Caused by Fusarium oxysporum f. sp. cubense Tropical Race 4 in China.

Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense (Foc), has been considered as the most devastating disease affecting bananas (Musa spp.) worldwide. A highly virulent strain of Foc, known as tropical race 4 (TR4), has been detected in the southeast Asia in the 1990s, and has since spread to western Asia, Australia, the Middle East, southern Africa, and South America (Viljoen et al. 2020). Foc TR4 can cause severe yield losses in Cavendish (AAA), Gros Michel (AAA), Silk (AAB), Pisang Awak (ABB) and Bluggoe (ABB) bananas (Ploetz et al. 2006). However, cooking bananas such as plantain (AAB) and Matooke (AAA) bananas, appear to be resistant (Zuo et al. 2017). Iholena bananas (AAB), a subgroup of varieties related to plantains (also known as Pacific plantains), is an important staple food in the Pacific Islands where it was domesticated. It is also popular in Peru, probably due to its nutritional value (Kepler et al. 2011) and is wildly cultivated in other South American countries (Dita et al. 2013). In December 2019, typical symptoms of banana Fusarium wilt were observed on Iholena accession 'Pacific Plantain' (ITC0210) in experimental fields located in Dongguan, Guangdong Province of China. The symptoms included leaf yellowing and pseudostem splitting. The vascular tissue inside the pseudostems was dark red to brown, and the inner rhizomes yellowish-brown. Vascular tissues from three diseased plants were sampled aseptically and placed on potato dextrose agar (PDA) containing 0.05 g/liter kanamycin. Fungal colonies typical of F. oxysporum developed rapidly, with purple-tinged white aerial mycelia and an abundance of microconidia borne in false heads on short microconidia (Nelson et al. 1983). Chlamydospores were produced singly or in pairs in hyphae and macroconidia. Molecular identification was performed using Foc race 4-specific primers (Lin et al. 2009), Foc TR4-specific primers (Dita et al. 2010), Foc race 1 and Foc STR4-specific primers (Ndayihanzamaso et al. 2020). Amplicons of expected sizes were obtained for Foc TR4 and race 4, but not for Foc race 1 and STR4. Sequencing of theITS and 18S rDNA from the three Iholena isolates and BLAST result showed a 100% similarity to the Foc TR4 reference sequences in GenBank (Foc II5, PRJNA73539 and PRJNA56513) to prove that the isolates were Foc TR4. Pathogenicity of the three isolates from Iholena bananas was determined by infecting 4-month-old Cavendish cv. 'Grand Nain' bananas and three Iholena accessions, 'Pacific Plantain' 'Tigua' and 'Uzakan', under greenhouse conditions by root immersion in a Foc conidial suspension and soil drenching at 106 conidia/ml (Dita, 2010). Control plants were treated with sterile distilled water. Three replications of five plantlets were used for each accession. After 35 days, the inoculated plantlets developed typical Fusarium wilt symptoms such as yellowing of the older leaves and discoloration of the inner rhizome. The control plants did not develop symptoms. To complete Koch's postulates, the fungus was re-isolated from inoculated plants and identified as Foc TR4 by PCR (Dita et al, 2010). The susceptibility of 'Tigua' and 'Uzakan' was also confirmed in Foc TR4-infested field trials, with both accessions developing severe Fusarium wilt symptoms. The susceptibility of Iholena bananas to Foc TR4 is of significant concern to all countries where this subgroup is cultivated for major food source, including Peru and other South American countries.

The Population of Fusarium oxysporum f. sp. cubense in Brazil Is Not Structured by Vegetative Compatibility Group or by Geographic Origin.

Fusarium wilt, caused by the soilborne fungus Fusarium oxysporum f. sp. cubense (Foc), is considered one of the most destructive diseases of bananas in Brazil. In this study, a collection of 194 monosporic isolates from several banana-producing regions located in different climatic zones along a south-to-north transect in Brazil was formed to assess the genetic structure of the population of Foc. The isolates underwent pathogenicity tests, PCR diagnosis for the detection of tropical race 4, and screening of SIX homolog genes that produce putative effector proteins. The vegetative compatibility group (VCG) of 119 isolates was determined by pairing against 17 internationally known VCG-tester strains. A group of 158 isolates was selected for simple sequence repeat (SSR) genotyping. There was moderate diversity of Foc in Brazil. Eight VCGs were identified: 0120, 0122, 0124, 0125, 0128, 01215, 01220, and 01222, of which 78% of isolates belong to a single VCG, whereas 22% of isolates are assigned to multiple VCGs, belonging to complexes of VCGs. The distribution of VCGs is uneven and independent of the banana genotype. The isolates of a VCG shared a similar profile of SIX homologs, but there was no association with geographic region. Four SSR loci were polymorphic, and, on average, 7.5 alleles were detected per locus. Thirty-five multilocus genotypes (MLGs) were identified. There was no association between VCG and MLGs, and no genetic structure of the population of Foc in Brazil was detected.

Characterization and Antagonistic Effect of Culturable Apple-Phyllosphere Endophytic Bacteria from the Cold Plateau in Yunnan, China

The endophytic bacteria in apple leaves from apple-producing areas of Yunnan, China were isolated and identified on the basis of bacterial colony morphology and nucleotide sequences of 16S rRNA and rpoB genes. The endophytic bacterial isolates with nitrogen, phosphorus, and potassium utilization abilities were screened by culturing on functional media. A total of 5709 isolates of culturable endophytic bacteria (CEB) were isolated from 30 apple leaf samples collected from different regions. A total of 39 CEB representative isolates were identified as Bacillus velezensis, B. subtilis, B. licheniformis, B. safensis, B. pumilus, and Priestia megaterium. Among them, B. velezensis and B. subtilis were the main CEB, accounting for 55.00% and 34.37%, respectively, which exhibited potential inhibition on not only the main apple disease pathogens of Alternaria alternata, Valsa mali, Fusarium oxysporum, and Rosellinia necatrix, but also some important and uncontrollable phytopathogens, including F. oxysporum f. sp. cubense that causes banana Fusarium wilt, and Phytophthora nicotianae that causes tobacco black shank. Among these isolated endophytic bacteria species, a total of 10 strains, including b3, b4, b16, b17, b20, and b23 of B. subtilis, b7, b24, and b28 of B. licheniformis, and b38 of B. velezensis, can fix nitrogen; 8 strains, including b7 and b28 of B. licheniformis, b5, b10, and b23 of B. subtilis, b8 of B. safensis, and b6 of Priestia megaterium, could dissolve inorganic phosphorus; 11 strains, including b9, b12, b14, b30, b34, and b43 of B. velezensis, b6 of Priestia megaterium, and b17, b18, b20, and b26 of B. subtilis, could degrade organic phosphorus; and 5 strains, including b4, b5, and b26 of B. subtilis, and b7 and b28 of B. licheniformis could dissolve potassium. These strains are valuable resources of endophytic bacteria that have adapted to the ecological environment of the Cold Plateau apple-production area and could be used as plant disease biocontrol agents and biofertilizers of crops. The culturable phyllosphere endophytes in apple leaves relate to geographic locations, apple varieties, and environment, providing the basis to explain the mechanisms underlying the establishment of apple endophyte diversity and may help to devise apple disease management strategies.

Multi-site fungicides suppress banana Panama disease, caused by Fusarium oxysporum f. sp. cubense Tropical Race 4.

Global banana production is currently challenged by Panama disease, caused by Fusarium oxysporum f.sp. cubense Tropical Race 4 (FocTR4). There are no effective fungicide-based strategies to control this soil-borne pathogen. This could be due to insensitivity of the pathogen to fungicides and/or soil application per se. Here, we test the effect of 12 single-site and 9 multi-site fungicides against FocTR4 and Foc Race1 (FocR1) in quantitative colony growth, and cell survival assays in purified FocTR4 macroconidia, microconidia and chlamydospores. We demonstrate that these FocTR4 morphotypes all cause Panama disease in bananas. These experiments reveal innate resistance of FocTR4 to all single-site fungicides, with neither azoles, nor succinate dehydrogenase inhibitors (SDHIs), strobilurins or benzimidazoles killing these spore forms. We show in fungicide-treated hyphae that this innate resistance occurs in a subpopulation of "persister" cells and is not genetically inherited. FocTR4 persisters respond to 3 μg ml-1 azoles or 1000 μg ml-1 strobilurins or SDHIs by strong up-regulation of genes encoding target enzymes (up to 660-fold), genes for putative efflux pumps and transporters (up to 230-fold) and xenobiotic detoxification enzymes (up to 200-fold). Comparison of gene expression in FocTR4 and Zymoseptoria tritici, grown under identical conditions, reveals that this response is only observed in FocTR4. In contrast, FocTR4 shows little innate resistance to most multi-site fungicides. However, quantitative virulence assays, in soil-grown bananas, reveals that only captan (20 μg ml-1) and all lipophilic cations (200 μg ml-1) suppress Panama disease effectively. These fungicides could help protect bananas from future yield losses by FocTR4.

Soil abiotic attributes related to fusarium wilt of bananas

Soil abiotic attributes related to fusarium wilt of bananas

Review on Broken-down Resistance to Diseases and Its Management; the Hidden Challenge in Breeding and Production of Banana and Plantains in Developing Countries

Resistant breakdown is the genetic vulnerability that is devastating agriculture breeding and production of banana worldwide, therefore threateningburgeoning population.It takes 15 to 20 years for banana breeding pipeline and other stakeholders to release a cultivar that is fully evaluated to farmers. Disease like fusarium wilt disease (race 1) was reported to wipe away Gros Michel and the Tropical Race 4 (TR4) has wiped away all cultivars which were resistant to race1. Again banana breeding for resistant to sigatoka successively bred and released many hybrids but of recently of these hybrids including FHIA hybrids, Yagambi KM 5, Paka, young Calcutta 4 and T8 has lost their resistant to sigatoka. Due to political and commercial pressures, it is true that most of the released resistant cultivars are from single effective genes. Though durable resistance with a single dominant gene has been a serious challenge to achieve in breeding, this is because of broken-down resistance. This review used online resource to identify some causes of broken resistance in banana and provided some possible solutions to increase durability. Causes of broken resistance includes the practice of monoculture in large area, illegal use of chemicals, multiple infections, evolution of pathogens as the result of recombination, mutations, nature of interaction exhibited by released cultivars, low genetic base in banana, gene flow, through introductions of pathogens and climate change. It is widely accepted that different agronomic practices combined with strategic breeding and release of cultivars can elongate durability of resistant cultivars to pathogens in agricultural system. Through all the literature searched it is being unveiled yet the factors that govern quality and durability of resistance in resistant cultivars. I hereby conclude that breeding for resistance to diseases in banana should go par pursue with other disease management strategies. This is aimed at increasing durability of resistance to diseases in this highly expensive produced banana and plantain hybrids.

Biofertilizer made from a mixed microbial community can enhance the suppression of fusarium wilt of banana when combined with acid soil ameliorant

Biofertilizer made from a mixed microbial community can enhance the suppression of fusarium wilt of banana when combined with acid soil ameliorant

Discovery of Niphimycin C from Streptomyces yongxingensis sp. nov. as a Promising Agrochemical Fungicide for Controlling Banana Fusarium Wilt by Destroying the Mitochondrial Structure and Function.

Banana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense (Foc) is the most destructive soil-borne fungal disease. Tropical race 4 (Foc TR4), one of the strains of Foc, can infect many commercial cultivars, which represents a threat to global banana production. Currently, there are hardly any effective chemical fungicides to control the disease. To search for natural product-based fungicides for controlling banana Fusarium wilt, we identified a novel strain Streptomyces yongxingensis sp. nov. (JCM 34965) from a marine soft coral, from which a bioactive compound, niphimycin C, was isolated using an activity-guided method. Niphimycin C exhibited a strong antifungal activity against Foc TR4 with a value of 1.20 μg/mL for EC50 and obviously inhibited the mycelial growth and spore germination of Foc TR4. It caused the functional loss of mitochondria and the disorder of metabolism of Foc TR4 cells. Further study showed that niphimycin C reduced key enzyme activities of the tricarboxylic acid (TCA) cycle and the electron transport chain (ETC). It displayed broad-spectrum antifungal activities against the selected 12 phytopathogenic fungi. In pot experiments, niphimycin C reduced the disease indexes in banana plantlets and inhibited the infection of Foc TR4 in roots. Hence, niphimycin C could be a promising agrochemical fungicide for the management of fungal diseases.

Uncontained spread of Fusarium wilt of banana threatens African food security.

Uncontained spread of Fusarium wilt of banana threatens African food security.

Induced resistance to Fusarium wilt of banana caused by Tropical Race 4 in Cavendish cv Grand Naine bananas after challenging with avirulent Fusarium spp.

In the last century, Fusarium wilt of banana (FWB) destroyed the banana cultivar Gros Michel. The Cavendish cultivars saved the global banana industry, and currently they dominate global production (~50%) and the export trade (~95%). However, a new strain called Tropical Race 4 (TR4) surfaced in the late 1960’s, spread globally and greatly damages Cavendish plantations as well as manifold local varieties that are primarily grown by small holders. Presently, there is no commercially available replacement for Cavendish and hence control strategies must be developed and implemented to manage FWB. Here, we studied whether it is possible to induce resistance to TR4 by pre-inoculations with different Fusarium spp. Only pre-treatments with an avirulent Race 1 strain significantly reduced disease development of TR4 in a Cavendish genotype and this effect was stable at various nutritional and pH conditions. We then used transcriptome analysis to study the molecular basis of this response. Several genes involved in plant defence responses were up-regulated during the initial stages of individual infections with TR4 and Race 1, as well as in combined treatments. In addition, a number of genes in the ethylene and jasmonate response pathways as well as several gibberellin synthesis associated genes were induced. We observed upregulation of RGA2 like genes in all treatments. Hence, RGA2 could be a key factor involved in both R1 and TR4 resistance. The data support the hypothesis that activating resistance to Race 1 in Cavendish bananas affects TR4 development and provide a first insight of gene expression during the interaction between various Fusarium spp. and banana.

Molecular, Histological and Histochemical Responses of Banana Cultivars Challenged with Fusarium oxysporum f. sp. cubense with Different Levels of Virulence.

Fusarium wilt caused by Fusarium oxysporum f. sp. cubense (Foc) is the most limiting factor in the banana agribusiness worldwide. Therefore, studies regarding pathogen attack mechanisms, and especially host defense responses, in this pathosystem are of utmost importance for genetic breeding programs in the development of Foc-resistant banana cultivars. In this study, analysis at the molecular, histological and histochemical levels of the Musa spp. x Foc interaction was performed. Three Foc isolates representative of race 1 (R1), subtropical race 4 (ST4) and isolate 229A, which is a putative ST4, were inoculated in two Prata-type cultivars (Prata-Anã and BRS Platina) and one cultivar of the Cavendish type (Grand Naine). Of seven genes related to plant–pathogen interactions, five were overexpressed in ‘BRS Platina’ 12 h after inoculation (HAI) with Foc R1 and ST4 but had reduced or negative expression after inoculation with Foc 229A, according to RT–qPCR analyses. While hyphae, mycelia and spores of the Foc 229A isolate grow towards the central cylinder of the Grand Naine and Prata-Anã cultivars, culminating in the occlusion of the xylem vessels, the BRS Platina cultivar responds with increased presence of cellulose, phenolic compounds and calcium oxalate crystals, reducing colonization within 30 days after inoculation (DAI). In general, these data indicate that the cultivar BRS Platina has potential for use in banana-breeding programs focused on resistance to Foc tropical race 4 (TR4) and in aggregating information on the virulence relationships of the Foc pathogen and the defense responses of banana plants after infection.

FoCupin1, a Cupin_1 domain-containing protein, is necessary for the virulence of Fusarium oxysporum f. sp. cubense tropical race 4.

Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) is an important soilborne fungal pathogen that causes the most devastating banana disease. Effectors secreted by microbes contribute to pathogen virulence on host plants in plant-microbe interactions. However, functions of Foc TR4 effectors remain largely unexplored. In this study, we characterized a novel cupin_1 domain-containing protein (FoCupin1) from Foc TR4. Sequence analysis indicated that the homologous proteins of FoCupin1 in phytopathogenic fungi were evolutionarily conserved. Furthermore, FoCupin1 could suppress BAX-mediated cell death and significantly downregulate the expression of defense-related genes in tobacco by using the Agrobacterium-mediated transient expression system. FoCupin1 was highly induced in the early stage of Foc TR4 infection. The deletion of FoCupin1 gene did not affect Foc TR4 growth and conidiation. However, FoCupin1 deletion significantly reduced Foc TR4 virulence on banana plants, which was further confirmed by biomass assay. The expression of the defense-related genes in banana was significantly induced after inoculation with FoCupin1 mutants. These results collectively indicate FoCupin1 is a putative effector protein that plays an essential role in Foc TR4 pathogenicity. These findings suggest a novel role for cupin_1 domain-containing proteins and deepen our understanding of effector-mediated Foc TR4 pathogenesis.

Small GTPase FoSec4-Mediated Protein Secretion Is Important for Polarized Growth, Reproduction and Pathogenicity in the Banana Fusarium Wilt Fungus Fusarium odoratissimum.

Apical secretion at hyphal tips is important for the growth and development of filamentous fungi. In this study, we analyzed the role of the Rab GTPases FoSec4 involved in the secretion of the banana wilt fungal pathogen Fusarium odoratissimum. We found that the deletion of FoSEC4 affects the activity of extracellular hydrolases and protein secretion, indicating that FoSec4 plays an important role in the regulation of protein secretion in F. odoratissimum. As a typical Rab GTPase, Sec4 participates in the Rab cycle through the conversion between the active GTP-bound state and the inactive GDP-bound state, which is regulated by guanine nucleate exchange factors (GEFs) and GTPase-activating proteins (GAPs). We further found that FoSec2 can interact with dominant-negative FoSec4 (GDP-bound and nucleotide-free form, FoSec4DN), and that FoGyp5 can interact with dominant active FoSec4 (GTP-bound and constitutively active form, FoSec4CA). We evaluated the biofunctions of FoSec4, FoSec2 and FoGyp5, and found that FoSec4 is involved in the regulation of vegetative growth, reproduction, pathogenicity and the environmental stress response of F. odoratissimum, and that FocSec2 and FoGyp5 perform biofunctions consistent with FoSec4, indicating that FoSec2 and FoGyp5 may work as the GEF and the GAP, respectively, of FoSec4 in F. odoratissimum. We further found that the amino-terminal region and Sec2 domain are essential for the biological functions of FoSec2, while the carboxyl-terminal region and Tre-2/Bub2/Cdc16 (TBC) domain are essential for the biological functions of FoGyp5. In addition, FoSec4 mainly accumulated at the hyphal tips and partially colocalized with Spitzenkörper; however, FoGyp5 accumulated at the periphery of Spitzenkörper, suggesting that FoGyp5 may recognize and inactivate FoSec4 at a specific location in hyphal tips.