# First report of fusarium wilt of cavendish bananas caused by Fusarium oxysporum f. sp. cubense tropical race 4 in the Grande Comoros Island

Mouzdalifa Mmadi, Abdou Azali Hamza, Diane Mostert, Isabelle Robène, Altus Viljoen

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Mouzdalifa Mmadi, Abdou Azali Hamza, Diane Mostert, Isabelle Robène, Altus Viljoen. First report of fusarium wilt of cavendish bananas caused by Fusarium oxysporum f. sp. cubense tropical race 4 in the Grande Comoros Island. Plant Disease, 2023, 107 (12), pp.4029. 10.1094/PDIS-07-23-1288-PDN. hal-05181653

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Diseases Caused by Fungi and Fungus-Like Organisms

First Report of Fusarium Wilt of Cavendish Bananas Caused by
Fusarium oxysporum f. sp. cubense Tropical Race 4 in the Grande
Comoros Island

Mouzdalifa Mmadi,<fnref n="1" /> Hamza Abdou Azali,<fnref n="1" /> Diane Mostert,<fnref n="2" />,†
Isabelle Robène,<fnref n="2" />,<fnref n="3" /> and Altus Viljoen<fnref n="2" />

**Funding:** This work was supported by two projects funded by the Food and Agriculture Organization of the United Nations within the project EDF 11 Project GCP/SFS/004/EC titled "Support towards the operationalization of the SADC Regional Agricultural Policy" and "Development of guidelines and provision of training on prevention and management of banana Fusarium wilt disease-Foc TR4." Additional funds were provided by INRAPE and the European Union's Horizon 2020 Research and Innovation Program within the project INDICANTS (INnovative DIAgnostiCs for bANana paThogens Surveillance) under grant agreement number 890856. Plant Dis. 107:4029, 2023; published online as https://doi.org/10.1094/ PDIS-07-23-1288-PDN. Accepted for publication 28 July 2023.

Fusarium wilt of banana, caused by the soil-borne pathogen *Fusarium oxysporum* f. sp. *cubense* (*Foc*), is a major constraint to banana production worldwide (Viljoen et al. 2020). Currently, Cavendish bananas are severely affected by *Foc* tropical race 4 (TR4) globally. In Africa, *Foc* TR4 was first detected in northern Mozambique in 2013 (Viljoen et al. 2020) and has since been found on the island of Mayotte in the Mozambique Channel off the coast of southeastern Africa (Aguayo et al. 2021). In early 2023, severe leaf yellowing and wilting of Cavendish banana plants were observed at several small holder farmer properties in Grande Comoros (Ngazidja, including those in Ntsinimoipanga (11.790053°S, 43.429733°E), Batou (11.499714°S, 43.364364°E), Madjeweni (11.441200°S, 43.387311°E), and Mdé (11.736545°S, 43.247634°E)). When the pseudostems of diseased plants were split open, a reddish-brown internal discoloration of the vascular tissue became apparent. Discolored strands of diseased plants were collected, and the causal agent was identified using DNA-based techniques, vegetative compatibility group (VCG) analysis, and pathogenicity testing. The samples were plated onto potato dextrose agar, and single-spored isolates were obtained and identified as *F. oxysporum* based on cultural and morphological characteristics. The

characteristics included the production of white fungal colonies with a
purple center, the infrequent production of macroconidia, but an abundance
of microconidia on short monophialides, and the production of terminal or
intercalary chlamydospores (Leslie and Summerell 2006). *Foc* TR4 was
identified from seven isolates by conventional (Dita et al. 2010) and quan-
titative (Matthews et al. 2020) PCR and loop-mediated isothermal amplifi-
cation (Ordóñez et al. 2019). All seven isolates were confirmed as members
of the VCG 01213/16 complex when *nit*-1 mutants of the unknown *Foc*
isolates were compatible with Nit-M mutants of the *Foc* VCG 01213 and
VCG 01216 tester strains. Two isolates were then selected for pathoge-
nicity testing, and 2-month-old tissue culture-derived Cavendish plants
(cv. Williams) were inoculated by using the method described by
Ndayihanzamaso et al. (2022). After 4 weeks, the *Foc* TR4-inoculated
plants produced wilting symptoms and internal rhizome discoloration
typical of Fusarium wilt. *Foc* TR4 was reisolated from the inoculated
plants and identified by qPCR (Matthews et al. 2020), thereby fulfilling
Koch's postulates. These results provide a scientific proof of the pres-
ence of *Foc* TR4 in a second island in the Comoros archipelago.
Comprehensive surveys will be conducted in all three of the Comoros
Islands to assess the presence and impact of *Foc* TR4 to implement
containment strategies. Collaborative initiatives and coordinated actions
among growers and other stakeholders are needed to prevent the spread
of *Foc* TR4 to more Southwest Indian Ocean islands and countries on the
East African coasts. Because of the importance of banana for food se-
curity and livelihoods and the unique genetic diversity of bananas found
on the Comoros Islands, the eradication and isolation of diseased bananas
in the short term and the screening of local banana varieties for *Foc*
TR4 resistance in the longer term are required.

References:

Aguayo, J., et al. 2021. Plant Dis. 105:219.

Dita, M. A., et al. 2010. Plant Pathol. 59:348.

Leslie, J., and Summerell, B. 2006. The *Fusarium* Laboratory Manual. Blackwell Publishing, Oxford, U.K.

Matthews, M. C., et al. 2020. PLoS One 15:e0236110.

Ndayihanzamaso, P., et al. 2022. Efficient Screening Techniques to Identify Mutants with Disease Resistance for Banana. Springer Nature, Berlin, Germany.

Ordóñez, N., et al. 2019. Plant Pathol. 68:1682.

Viljoen, A., et al. 2020. Page 159 in: Emerging Plant Diseases and Global Food Security. American Phytopathological Society, St. Paul, MN.

The author(s) declare no conflict of interest.

e-Xtra

Keywords: Cavendish banana, Fusarium wilt, Grande Comoros, tropical race 4

<footnote n="1">¹ Institut National de Recherché Pour l'Agriculture, la Pêche et l'Environnement (INRAPE), Ex-CEFADER, Mdé, Moroni, Comoros</footnote>

<footnote n="2">² Department of Plant Pathology, Matieland University, Stellenbosch 7602, South Africa</footnote>

<footnote n="3">³ CIRAD, UMR PVBMT, Réunion Island, Saint-Pierre 97410, France</footnote>

<footnote>†Indicates the corresponding author.
D. Mostert; diane@sun.ac.za</footnote>