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 (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 Bouéni ([WGS] 12° 54’ 25’’S, 45° 04’ 43” E). These included infected Cavendish banana (AAA) plants (cv. “Kontriké”). 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 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.

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a narrower molecular weight distribution by effectively removing the high molecular weight tail of the distribution. This results in a more Newtonian shear viscosity behavior permitting the use of lower processing temperatures and higher spinning speeds when processing into fibers or thin films. [8] In the case of HEPCs a similar vis-breaking treatment can be applied for the same reasons. The necessity of this step is due to the incapability of the catalyst system to provide low molecular weight material. While this step is necessary, its effect on the mechanical properties of the resultant impact copolymer is undesirable. [9,10] The effect of the visbreaking process on impact copolymers is not well understood as the chemical structure of these copolymers is highly complex. HEPCs contain varying distributions of ethylene-and propylene-rich regions. This presents challenges in predicting the manner in which the copolymers will be affected by vis-breaking. In contrast, the process and mechanism of vis-breaking for conventional polypropylene is well documented. [8,11-14] Controlled rheology (also referred to as vis-breaking) is based on chain scission induced by free radicals, exploiting the mechanism of oxidative degradation of polypropylene. As polyolefins in general are susceptible to oxidative and photochemical degradation, polymer modifications which make use of these radical reactions need precise decomposition rates depending on the processing conditions. Therefore radical sources with specific thermal decomposition temperatures and thus controlled radical initiation are ideal. The radical source is most often an organic peroxide such as dicumylperoxide, [14-16] 2,5dimethyl-2,5-di-tert-butylperoxyhexane (DHBP), [7,17,18] or cyclic peroxides such as 3,6,9-triethyl-3,6,9-trimethyl-1,4,7-triperoxonane (Trigonox 301) [9] which forms primary radicals following thermal decomposition. The cyclic peroxides have the advantage of not releasing volatile gases as in the case of the acyclic organic peroxides. [7,19] Since the radicals attack in a random fashion the statistical probability that a monomer in a longer chain reacts with a radical is greater since the distribution of chain sizes generally implies that monomers are more likely to occur in longer chains than shorter chains. This leads to break down of the longer chains and decrease of the overall molecular weight distribution. The use of inorganic peroxides has been reported in the literature [8] but has not been implemented industrially due to the high reactivity of these peroxides which require low reaction temperatures. This limits the applicability Solution 13 C nuclear magnetic resonance (NMR) is used in conjunction with in situ solid-state NMR to determine the effect of peroxide treatment on the chemical structure and morphology of ethylene−propylene copolymers. The copolymers contain increasing quantities of ethylene with the lowest ethylene content corresponding to pure isotactic polypropylene. The vis-breaking of heterophasic ethylene-propylene copolyme...