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Black Sigatoka, caused by Pseudocercospora fijiensis, is a major foliar disease of banana and plantain worldwide. There are few available data regarding the genetic diversity and population structure of the pathogen in East Africa, which are needed to design effective and durable disease management strategies. We genotyped 319 single-spore isolates of P. fijiensis collected from seven regions in Uganda and Tanzania and five isolates from Nigeria using 16 simple sequence repeat markers and mating type-specific primers. Isolates from each country and region within the country were treated as populations and subpopulations, respectively. A total of 296 multilocus genotypes (MLGs) were recovered, representing a clonal fraction of 7%. Subpopulations had a moderate level of genetic diversity (Hexp = 0.12 to 0.31; mean, 0.29). Mating type distribution did not deviate from equilibrium (MAT1-1: MAT1-2, 1:1 ratio) in Uganda; however, in Tanzania the mating types were not in equilibrium (4:1 ratio). The index of association tests (IA and r̄d) showed that all populations were at linkage equilibrium (P > 0.05), thus supporting the hypothesis of random association of alleles. These findings are consistent with a pathogen that reproduces both clonally and sexually. Low and insignificant levels of population differentiation were detected, with 90% of the variation occurring among isolates within subpopulations. The high intrapopulation variation has implications in breeding for resistance to P. fijiensis because isolates differing in aggressiveness and virulence are likely to exist over small spatial scales. Diverse isolates will be required for resistance screening to ensure selection of banana cultivars with durable resistance to Sigatoka in East Africa. [Formula: see text] Copyright © 2021 The Author(s). This is an open access article distributed under the CC BY 4.0 International license .

International audience; Scientific communication is facilitated by a data-driven, scientifically sound taxonomy that considers the end-user's needs and established successful practice. Previously (Geiser et al. 2013; Phytopathology 103:400-408. 2013), the Fusarium community voiced near unanimous support for a concept of Fusarium that represented a clade comprising all agriculturally and clinically important Fusarium species, including the F. solani Species Complex (FSSC). Subsequently, this concept was challenged by one research group (Lombard et al. 2015 Studies in Mycology 80: 189-245) who proposed dividing Fusarium into seven genera, including the FSSC as the genus Neocosmospora, with subsequent justification based on claims that the Geiser et al. (2013) concept of Fusarium is polyphyletic (Sandoval-Denis et al. 2018; Persoonia 41:109-129). Here we test this claim, and provide a phylogeny based on exonic nucleotide sequences of 19 orthologous protein-coding genes that strongly support the monophyly of Fusarium including the FSSC. We reassert the practical and scientific argument in support of a Fusarium that includes the FSSC and several other basal lineages, consistent with the longstanding use of this name among plant pathologists, medical mycologists, quarantine officials, regulatory agencies, students and researchers with a stake in its taxonomy. In recognition of this monophyly, 40 species recently described as Neocosmospora were recombined in Fusarium, and nine others were renamed Fusarium. Here the global Fusarium community voices strong support for the inclusion of the FSSC in Fusarium, as it remains the best scientific, nomenclatural and practical taxonomic option available.

Banana is a staple food and cash crop grown in East and Central Africa (ECA). The main banana varieties grown in ECA are the East African highland bananas (EAHB), although dessert/beer bananas such as Sukari Ndizi, Kayinja (Pisang Awak) and Gros Michel are also produced due to their high value at local markets. The Fusarium wilt fungus Fusarium oxysporum f. sp. cubense (Foc) causes disease of susceptible dessert/beer bananas, which significantly reduces yields. Banana Fusarium wilt is managed by excluding the pathogen from disease-free areas and by planting disease-resistant varieties in infested fields. Six phylogenetically closely-related vegetative compatibility groups (VCGs) of Foc, VCGs 0124, 0125, 0128, 01212, 01220 and 01222 are present in ECA, which all group together in Foc Lineage VI. Rapid and accurate detection of Foc Lineage VI strains is thus important to prevent its spread to disease-free areas. In this study, molecular markers specific to Foc Lineage VI were therefore developed. Primer sets were then combined in a multiplex PCR assay, and validated on a worldwide population of 623 known Foc isolates, other formae speciales and non-pathogenic Fusarium oxysporum isolates. The Foc Lineage VI multiplex PCR was used to identify Foc isolates collected in banana fields at five locations in Uganda and Tanzania. Foc Lineage VI DNA was detected at a concentration as low as 0.1 ng/μl, both in the absence and presence of banana DNA, and can therefore be used as an accurate diagnostic tool for Foc Lineage VI strains.

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.

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.

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.

Summary Fusaric acid (FSA) is a phytotoxin produced by several Fusarium species and has been associated with plant disease development, although its role is still not well understood.Mutation of key genes in the FSA biosynthetic gene (FUB) cluster in Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) reduced the FSA production, and resulted in decreased disease symptoms and reduced fungal biomass in the host banana plants.When pretreated with FSA, both banana leaves and pseudostems exhibited increased sensitivity to Foc TR4 invasion. Banana embryogenic cell suspensions (ECSs) treated with FSA exhibited a lower rate of O2 uptake, loss of mitochondrial membrane potential, increased reactive oxygen species (ROS) accumulation, and greater nuclear condensation and cell death. Consistently, transcriptomic analysis of FSA‐treated ECSs showed that FSA may induce plant cell death through regulating the expression of genes involved in mitochondrial functions.The results herein demonstrated that the FSA from Foc TR4 functions as a positive virulence factor and acts at the early stage of the disease development before the appearance of the fungal hyphae in the infected tissues.

Fusarium oxysporum f. sp. cubense (Foc) is a fungus causing Fusarium wilt of banana (Musa spp.). The fungus is divided into three races and 24 vegetative compatibility groups (VCG) of which VCG 01213/16, commonly known as Foc tropical race 4 (Foc TR4), is of particular concern. Foc TR4 severely affects Cavendish (AAA) bananas, which comprise about 50% of all bananas produced globally, as well as many varieties susceptible to the other races of Foc. The pathogen was restricted to Southeast Asia and Australia until 2012, where after it has been detected in the Middle East, Mozambique in Africa, and Colombia in South America (Viljoen et al. 2020). Here we report the first detection of Foc TR4 in the French department of Mayotte, located in the Indian Ocean. In September 2019, leaf yellowing and wilting symptoms were observed in individual plants of the banana subgroups Silk (AAB) (cv. "Kissoukari") and Bluggoe (ABB) (cv. "Baraboufaka"). The symptomatic individuals were found in private gardens in the village of Poroani in Southwest Mayotte (World Geodetic System [WGS] 12° 53' 31.83''S, 45° 8' 30.98" E). When the pseudostems of symptomatic plants were split open, dark red to brown vascular discoloration was observed. Pseudostem tissue samples were collected and identified as Foc TR4 with the real-time PCR assay developed by Aguayo et al. (2017). Sections of the pseudostem samples were surface sterilized and used to isolate the fungus on potato dextrose agar (PDA) medium. Isolates were identified as F. oxysporum based on cultural and morphological characteristics as described in Leslie and Summerell (2006), which included fluffy aerial mycelia on PDA and the presence of short monophialides conidigenous cells bearing microconidia arranged in false heads. Abundant chlamydospores were also produced on synthetic nutrient poor agar (SNA) media. Single-spored isolates were used to develop nit mutants for vegetative compatibility group (VCG) testing (Correll 1991; Puhalla 1985). The isolates were confirmed as VCG 01213/16 as formation of heterokaryons was obtained with the nit mutants of the universal Foc TR4 tester. Two VCG 01213/16 isolates were then selected for pathogenicity testing by inoculating 2-month-old tissue culture-derived Cavendish plants, using the method described by Viljoen et al. (2017). After 10 weeks, the Foc TR4-inoculated plants produced wilting symptoms and internal rhizome discoloration typical of Fusarium wilt. Fusarium oxysporum was re-isolated from the inoculated plants and identified as Foc TR4/VCG 01213/16 by PCR (Dita et al. 2010; Matthews et al. 2020), thereby fulfilling Koch's postulates. Local authorities have destroyed the infected plants, and have undertaken an extensive survey to determine the distribution of Foc TR4 on the island. Three additional positive cases, identified with the real-time PCR assay of Aguayo et al. (2017), were found in the localities of Koungou ([WGS] 12° 44' 03''S, 45° 12' 08" E) and Boueni ([WGS] 12° 54' 25''S, 45° 04' 43" E). These included infected Cavendish banana (AAA) plants (cv. "Kontrike"). This is the first time that Foc TR4 has been found on a banana variety other than Cavendish when newly detected in a country. Considering the proximity of Mayotte to other islands of the Comoros archipelago, Madagascar and the East African coast, where banana is considered an important staple, this report describes a serious threat to banana production and the livelihoods of people in the region.

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 a ected 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. ispartof: Plants vol:9 issue:9 ispartof: location:Switzerland status: Published online

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 wilt of banana, caused by the soil-borne fungus Fusarium oxysporum f. sp. cubense (Foc), is a major constraint to banana production worldwide. A strain of the fungus that affects Cavendish and other dessert bananas in the tropics, called Foc tropical race 4 (TR4; VCG 01213/16), has been confined to five Asian countries (Indonesia, Malaysia, Philippines, mainland China, and Taiwan) for more than three decades. Cavendish production is now being expanded in Asia to Laos, Myanmar, and Vietnam, where local varieties still dominate the market. This is owing to an increase in Cavendish banana consumption and a decline in areas of production caused by Foc TR4 in China. The expansion of Cavendish production in Southeast Asia, however, has increased the risk of Foc TR4 being introduced into new countries. Leaf-yellowing symptoms typical of banana Fusarium wilt were observed in three provinces in northern Vietnam along the Red River that originates in the Yunnan province of China, namely Hanoi (October 2014), Hung Yen (October 2015), and Lao Cai (October 2015). When cut open, pseudostems displayed a dark-red to brown discoloration of vascular tissue, and the inner rhizome revealed a ring of yellow-brown staining. Samples of symptomatic strands from pseudostems were collected to identify the causal agent by morphological, molecular, and vegetative compatibility group (VCG) identification. The samples were first plated onto potato dextrose agar (PDA) containing streptomycin for fungal isolation. The cultures were then purified, single-spored, and maintained at the culture collection of the Department of Plant Pathology at Stellenbosch University in South Africa. Eight Fusarium isolates obtained were identified to species level on PDA and carnation leaf agar plates according to their cultural and spore morphology (Nelson et al. 1983). For molecular identification, total DNA was extracted and amplified with Foc TR4-specific primers (Dita et al. 2010) and Foc race 4-specific primers (Lin et al. 2009). VCG testing was performed according to the method of Puhalla (1985) by pairing nit-1 and nit-3 mutants of the isolates from Vietnam with nit-M testers of VCGs 01213, 01216, and 01213/16. Pathogenicity testing was performed by replanting Cavendish tissue culture plantlets at the six-leaf stage in sand mixed with corn powder, which was colonized by the individual Fusarium isolates from Vietnam, at a ratio of 19:1. Control plants were treated with sterile distilled water. The identity of the Vietnamese isolates was confirmed as F. oxysporum, whereas PCR and VCG analysis characterized six of them as VCG 01213/16 strains. After 6 weeks, plants inoculated with the VCG 01213/16 isolates produced typical symptoms of Fusarium wilt, so Koch's postulates were completed. The occurrence of Foc TR4 in Vietnam can have a significant economic impact to agricultural production, because investments were made to replace citrus, longan, and corn fields with Cavendish plantations. Foc TR4 also poses a threat to local banana varieties, and these varieties should therefore be evaluated for resistance to the fungus. The potential spread of Foc TR4 in Vietnam should be minimized by surveillance, public awareness campaigns, risk assessment, and containment efforts.

The popular Cavendish banana (Musa spp., AAA) constitutes about 45% of all bananas grown worldwide (Lescot, 2015). Mainland China is one of the leading producers of Cavendish bananas, and to satisfy local demand for the fruit, commercial production is expanding into neighbouring countries such as Laos, Myanmar and Vietnam. In Laos, local banana varieties such as “kuay nam” (Silk, AAB), “kuay hom” (local Cavendish, AAA) and “kuay klai” (Horn Plantain, AAB) are preferentially grown for food and income generation. The expansion of Cavendish production from China into Laos, therefore, presents significant risks to these varieties, such as the introduction of Fusarium oxysporum f. sp. cubense tropical race 4 (TR4; VCG 01213/16), a soil-borne fungus that causes severe epidemics and crop losses in Cavendish plantations in southern Chinese provinces. In November 2016, Laos Department of Agriculture staff reported wilting plants from Luang Namtha and Borkeo provinces. In February 2017, yellow leaf symptoms typical...

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.