TR4-infected banana shows blackened, discoloured and weakened vascular tissue within the stem.
Photo: ©TR4GN

Fusarium TR4 threatens banana production

Fusarium Tropical Race 4 (TR4) has arrived in Latin America. It is a major threat to banana producers, many of them are smallholder farmers. There is no viable, fully effective treatment of soil or plants to control or cure Fusarium in the field.

After its first detection in Asia more than 20 years ago, and its subsequent shift to Africa in 2013, TR4 has finally arrived in Latin America. On August 8, the Colombian Institute of Agriculture (ICA) officially announced that TR4 has been found on six farms in La Guajira, the North East of the country. Subsequently, the ICA announced the declaration of a National Emergency. 

A phytosanitary alert for Fusarium Tropical Race 4 (TR4) in Latin America and the Caribbean was published by the TR4 Task Force on 15 August 2019. The TR4 Task Force is part of the World Banana Forum (WBF) of the Food and Agriculture Organization of the United Nations (FAO), and established the TR4 Global Network (TR4GN), a knowledge hub on the prevention of the spread of TR4.

TR4 is considered as the world’s greatest threat to banana production. If unchecked, it can wipe out an entire plantation. The pathogen can be transmitted through planting materials, movement of infested soil particles by any means such as shoes, vehicles or through water. The fungus is able to remain dormant in the soil for decades. 

Infected suckers do not show symptoms

The spores infect the plant through the roots and colonise the plant’s xylem vessels, blocking the flow of water and nutrients. The characteristic symptom of Fusarium is blackened, discoloured and weakened vascular tissue within the stems of the plant. The discolouration varies from pale yellow in the early stages to dark red and black in the later stages. Internal symptoms initially develop in the feeder roots and rhizomes and then in the plant’s pseudostem. 

Externally, the first signs of the disease are wilted plants with yellowing older leaves around the margins. Sometimes the leaves remain green longer on the petiole, but as the disease progresses, they eventually collapse forming a ‘skirt’ around the pseudostem before falling off. New leaves may have irregular, pale margins and wrinkled blades. 

The disease may cause the pseudostem to wilt or collapse. Infected suckers (used for seeding new plants) and rhizomes do not start showing symptoms of the infection until they are around four months old. Therefore, the fungus can easily spread also through infected suckers which may be symptomless. Fruit shows no symptoms of disease. 

There are no effective control measures

Fusarium TR4 cannot be controlled by common chemical or cultural management practices. Available methods for disease containment are not fully efficient on TR4; and alternative options are still at the evaluation stage. The only currently available preventive measure is quarantine: preventing the transfer of infected soil or plant material from infected areas to TR4-free areas. According to WBF, crop diversification as well as variety enrichment in more sustainable banana and plantain production systems are key to reducing vulnerability.

The social consequences of Fusarium can be severe: bananas are an important source of food, income, employment and government revenues in many tropical countries. The vast majority of producers are smallholder farmers who grow the crop for either home consumption or local markets. Virtually all export bananas, and also a considerable part of the bananas cultivated for own consumption or local markets are Cavendish bananas or other cultivars susceptible to Fusarium TR4. There are no resistant varieties yet that can replace Export Cavendish Banana, according to WBF. 

(TR4GN/ile)

More information at http://www.fao.org/world-banana-forum/fusariumtr4/tr4-global-network/en/