Search

Fusarium wilt of banana is a devastating disease that has decimated banana production worldwide. Host resistance to Fusarium oxysporum f. sp. Cubense (Foc), the causal agent of this disease, is genetically dissected in this study using two Musa acuminata ssp. Malaccensis segregating populations, segregating for Foc Tropical (TR4) and Subtropical (STR4) race 4 resistance. Marker loci and trait association using 11 SNP-based PCR markers allowed the candidate region to be delimited to a 12.9 cM genetic interval corresponding to a 959 kb region on chromosome 3 of ‘DH-Pahang’ reference assembly v4. Within this region, there was a cluster of pattern recognition receptors, namely leucine-rich repeat ectodomain containing receptor-like protein kinases, cysteine-rich cell-wall-associated protein kinases, and leaf rust 10 disease-resistance locus receptor-like proteins, positioned in an interspersed arrangement. Their transcript levels were rapidly upregulated in the resistant progenies but not in the susceptible F2 progenies at the onset of infection. This suggests that one or several of these genes may control resistance at this locus. To confirm the segregation of single-gene resistance, we generated an inter-cross between the resistant parent ‘Ma850’ and a susceptible line ‘Ma848’, to show that the STR4 resistance co-segregated with marker ‘28820’ at this locus. Finally, an informative SNP marker 29730 allowed the locus-specific resistance to be assessed in a collection of diploid and polyploid banana plants. Of the 60 lines screened, 22 lines were predicted to carry resistance at this locus, including lines known to be TR4-resistant, such as ‘Pahang’, ‘SH-3362’, ‘SH-3217’, ‘Ma-ITC0250’, and ‘DH-Pahang/CIRAD 930’. Additional screening in the International Institute for Tropical Agriculture’s collection suggests that the dominant allele is common among the elite ‘Matooke’ NARITA hybrids, as well as in other triploid or tetraploid hybrids derived from East African highland bananas. Fine mapping and candidate gene identification will allow characterization of molecular mechanisms underlying the TR4 resistance. The markers developed in this study can now aid the marker-assisted selection of TR4 resistance in breeding programs around the world.

Fusarium wilt, caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc), poses a major threat to banana production globally. A variant of Foc that originated in Southeast Asia, called tropical race 4 (TR4), was detected on a Cavendish banana export plantation (Metocheria) in northern Mozambique in 2013. Foc TR4 was rapidly disseminated on the farm, and affected approximately half a million plants within 3 years. The fungus was also detected on a second commercial property approximately 200 km away (Lurio farm) a year later, and on a small-grower’s property near Metocheria farm in 2015. Surveys in Mozambique showed that non-Cavendish banana varieties were only affected by Foc race 1 and race 2 strains. The testing of Cavendish banana somaclones in northern Mozambique revealed that GCTCV-119 was most resistant to Foc TR4, but that GCTCV-218 produced better bunches. The occurrence of Foc TR4 in northern Mozambique poses a potential threat to food security on the African continent, where banana is considered a staple food and source of income to millions of people. Cavendish somaclones can be used, in combination with integrated disease management practices, to replace susceptible Cavendish cultivars in southern Africa. The comprehensive testing of African cooking bananas for resistance to Foc TR4 is required, along with the improvement of biosecurity and preparedness of growers on the African continent. Significance: • This paper presents the first official report of the invasive pest Foc TR4 in Africa. • The spread of Foc TR4 on Cavendish banana farms in Mozambique was documented. • Banana varieties that could replace susceptible Cavendish bananas were identified.

Fusarium wilt, caused by the fungus Fusarium oxysporum f. sp. cubense (Foc), poses a major threat to global banana production. The tropical race 4 (TR4) variant of Foc is a highly virulent form with a large host range, and severely affects Cavendish bananas. Foc TR4 was recently observed within the Greater Mekong Subregion, after Chinese private companies expanded Cavendish production to the region. In this study, extensive surveys conducted across Laos and Vietnam show that Foc TR4 is still mainly constricted to the northern regions of these countries and is limited to Cavendish cultivation settings. In Laos, Foc TR4 is associated with large-scale Cavendish plantations owned by or involved with Chinese companies through which infected planting material could have been imported. In Vietnam, mostly small-holder Cavendish farmers and backyard gardens were affected by Foc TR4. In Vietnam, no direct link is found with Chinese growers, and it is expected the pathogen mainly spreads through local and regional movement of infected planting materials. Foc TR4 was not recorded on banana cultivars other than Cavendish. The extensively cultivated ‘Pisang Awak’ cultivar was solely infected by VCGs belonging to Foc race 1 and 2, with a high occurrence of VCG 0123 across Laos, and of VCG 0124/5 in Vietnam. Substantial diversity of Foc VCGs was recorded (VCGs 0123, 0124/5, 01218 and 01221) from northern to southern regions in both countries, suggesting that Fusarium wilt is well established in the region. Interviews with farmers indicated that the local knowledge of Fusarium wilt epidemiology and options for disease management was limited. Clear communication efforts on disease epidemiology and management with emphasis on biosecurity practices need to be improved in order to prevent further spread of Foc TR4 to mixed variety smallholder settings.

Fusarium oxysporum f. sp. cubense (Foc) is a soil-borne fungus that causes Fusarium wilt, a destructive plant disease that has resulted in devastating economic losses to banana production worldwide. The fungus has a complex evolutionary history and taxonomic repute and consists of three pathogenic races and at least 24 vegetative compatibility groups (VCGs). Surveys conducted in Asia, Africa, the Sultanate of Oman and Mauritius encountered isolates of F. oxysporum pathogenic to banana that were not compatible to any of the known Foc VCGs. Genetic relatedness between the undescribed and known Foc VCGs were determined using a multi-gene phylogeny and diversity array technology (DArT) sequencing. The presence of putative effector genes, the secreted in xylem (SIX) genes, were also determined. Fourteen novel Foc VCGs and 17 single-member VCGs were identified. The multi-gene tree was congruent with the DArT-seq phylogeny and divided the novel VCGs into three clades. Clustering analysis of the DArT-seq data supported the separation of Foc isolates into eight distinct clusters, with the suite of SIX genes mostly conserved within these clusters. Results from this study indicates that Foc is more diverse than hitherto assumed.

Fusarium oxysporum f. sp cubense (Foc), the causal agent of Fusarium wilt, is one of the most devastating constraints to banana production worldwide. The spread of Foc in water is particularly concerning, as infested water can rapidly contaminate disease-free areas. The objectives of this study were to investigate the survival of Foc in water and to test the effectiveness of water treatment with chlorine, ozone, UV, and peracetic acid. The study indicated that Foc spores can survive in water for more than 120 days, but that viability was reduced in stagnant water, probably due to anaerobic conditions when spores settled at the bottom. It is therefore recommended that surface water be extracted and treated before it is used for irrigation. The efficacy of all water treatments was reduced in the presence of soil, implying that water needs to be soil-free before treatment. The use of peracetic acid is recommended to treat Foc-contaminated water, as it is safe for use and does not require installation costs although it is effective at treating Foc-contaminated water, ozone would require significant input costs and chlorine can produce harmful disinfection by-products. UV would be impractical for field application because of the high doses required to eliminate Foc.

Banana is an important food crop and source of income in Africa. Sustainable production of banana, however, is at risk because of pests and diseases such as Fusarium wilt, caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc). Foc can be disseminated from infested to disease-free fields in plant material, water and soil. Early detection of Foc using DNA technologies is thus required to accurately identify the fungus and prevent its further dissemination with plants, soil and water. In this study, quantitative (q)PCR assays were developed for the detection of Foc Lineage VI strains found in central and eastern Africa (Foc races 1 and 2), Foc TR4 (vegetative compatibility groups (VCG) 01213/16) that is present in Mozambique, and Foc STR4 (VCG 0120/15) that occurs in South Africa. A collection of 127 fungal isolates were selected for specificity testing, including endophytic Fusarium isolates from banana pseudostems, non-pathogenic F. oxysporum strains and Foc isolates representing the 24 VCGs in Foc. Primer sets that proved to be specific to Foc Lineage VI, Foc TR4 and Foc STR4 were used to produce standard curves for absolute quantification, and the qPCR assays were evaluated based on the quality of standard curves, repeatability and reproducibility, and limits of quantification (LOQ) and detection (LOD). The qPCR assays for Foc Lineage VI, TR4 and STR4 were repeatable and reproducible, with LOQ values of 10-3-10-4 ng/μL and a LOD of 10-4-10-5 ng/μL. The quantitative detection of Foc strains in Africa could reduce the time and improve the accuracy for identifying the Fusarium wilt pathogen from plants, water and soil on the continent.

Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) causes Fusarium wilt of banana, the most devastating disease on a banana plant. The genome of Foc TR4 encodes many candidate effector proteins. However, little is known about the functions of these effector proteins on their contributions to disease development and Foc TR4 virulence. Here, we discovered a secreted metalloprotease, FocM35_1, which is an essential virulence effector of Foc TR4. FocM35_1 was highly upregulated during the early stages of Foc TR4 infection progress in bananas. The FocM35_1 knockout mutant compromised the virulence of Foc TR4. FocM35_1 could interact with the banana chitinase MaChiA, and it decreased banana chitinase activity. FocM35_1 induced cell death in Nicotiana benthamiana while suppressing the INF1-induced hypersensitive response (HR), and its predicted enzymatic site was required for lesion formation and the suppression to INF1-induced HR on N. benthamiana leaves. Importantly, treatment of banana leaves with recombinant FocM35_1 accelerates Foc TR4 infection. Collectively, our study provides evidence that metalloprotease effector FocM35 seems to contribute to pathogen virulence by inhibiting the host immunity.

Fusarium wilt, caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc) race 1, is a major disease of bananas in East Africa. Triploid East African Highland (Matooke) bananas are resistant to Foc race 1, but the response of diploid (Mchare and Muraru) bananas to the fungus is largely unknown. A breeding project was initiated in 2014 to increase crop yield and improve disease and pest resistance of diploid and triploid East African Highland bananas. In this study, eight Mchare cultivars were evaluated for resistance to Foc race 1 in the field in Arusha, Tanzania. In addition, the same eight Mchare cultivars, as well as eight Muraru cultivars, 27 Mchare hybrids, 60 Matooke hybrids and 19 NARITA hybrids were also screened in pot trials. The diploid Mchare and Muraru cultivars were susceptible to Foc race 1, whereas the responses of Mchare, NARITAs and Matooke hybrids ranged from susceptible to resistant. The Mchare and Matooke hybrids resistant to Foc race 1 can potentially replace susceptible cultivars in production areas severely affected by the fungus. Some newly bred Matooke hybrids became susceptible following conventional breeding, suggesting that new hybrids need to be screened for resistance to all Foc variants.

Fusarium oxysporum formae specialis cubense (Foc) is a soil-borne fungus that causes Fusarium wilt, which is considered to be the most destructive disease of bananas. The fungus is believed to have evolved with its host in the Indo-Malayan region, and from there it was spread to other banana-growing areas with infected planting material. The diversity and distribution of Foc in Asia was investigated. A total of 594 F. oxysporum isolates collected in ten Asian countries were identified by vegetative compatibility groups (VCGs) analysis. To simplify the identification process, the isolates were first divided into DNA lineages using PCR-RFLP analysis. Six lineages and 14 VCGs, representing three Foc races, were identified in this study. The VCG complex 0124/5 was most common in the Indian subcontinent, Vietnam and Cambodia; whereas the VCG complex 01213/16 dominated in the rest of Asia. Sixty-nine F. oxysporum isolates in this study did not match any of the known VCG tester strains. In this study, Foc VCG diversity in Bangladesh, Cambodia and Sri Lanka was determined for the first time and VCGs 01221 and 01222 were first reported from Cambodia and Vietnam. New associations of Foc VCGs and banana cultivars were recorded in all the countries where the fungus was collected. Information obtained in this study could help Asian countries to develop and implement regulatory measures to prevent the incursion of Foc into areas where it does not yet occur. It could also facilitate the deployment of disease resistant banana varieties in infested areas.

Fusarium oxysporum f. sp. cubense (Foc) is one of the most important threats to global banana production. Strategies to control the pathogen are lacking, with plant resistance offering the only long-term solution, if sources of resistance are available. Prevention of introduction of Foc into disease-free areas thus remains a key strategy to continue sustainable banana production. In recent years, strains of Foc affecting Cavendish bananas have destroyed plantations in a number of countries in Asia and in the Middle East, and one African country. One vegetative compatibility group (VCG), 01213/16, is considered the major threat to bananas in tropical and subtropical climatic conditions. However, other genetically related VCGs, such as 0121, may potentially jeopardize banana cultures if they were introduced into disease-free areas. To prevent the introduction of these VCGs into disease-free Cavendish banana-growing countries, a real-time PCR test was developed to accurately detect both VCGs. A previously described putative virulence gene was used to develop a specific combination of hydrolysis probe/primers for the detection of tropical Foc race 4 strains. The real-time PCR parameters were optimized by following a statistical approach relying on orthogonal arrays and the Taguchi method in an attempt to enhance sensitivity and ensure high specificity of the assay. This study also assessed critical performance criteria, such as repeatability, reproducibility, robustness, and specificity, with a large including set of 136 F. oxysporum isolates, including 73 Foc pathogenic strains representing 24 VCGs. The validation data demonstrated that the new assay could be used for regulatory testing applications on banana plant material and can contribute to preventing the introduction and spread of Foc strains affecting Cavendish bananas in the tropics.