/Tropical Race 4 (TR4) strain of Fusarium oxysporum f.sp. cubense, main threaten the banana industry

Tropical Race 4 (TR4) strain of Fusarium oxysporum f.sp. cubense, main threaten the banana industry

Tropical Race 4 (TR4) strain of Fusarium oxysporum f.sp. cubense is one of the main threats facing producers and workers in the banana industry. The pathogen causes Fusarium wilt in banana and is also known as “Panama disease”. TR4 has infested banana plantations in Taiwan, Mozambique, Indonesia, Malaysia, Jordan, Oman, Australia, Vietnam, Laos, and Myanmar. The disease wiped out the Gros Michel banana industry in Central America and the Caribbean, in the mid-twentieth century. The effects of Fusarium oxysporum f. sp. cubense Race 1 were overcome by a shift to resistant Cavendish cultivars, which are currently the source of 99 % of banana exports. The new strain of Fusarium oxysporum f.sp. cubense called Tropical race 4 has overcome resistance in Cavendish clones and caused epidemics in the tropics. It is a growing concern for the export industry and producers as it colonizes, infects and destroys Cavendish banana plants and many other varieties. Once present, the disease cannot be controlled by chemical or cultural management practices.
Available methods for disease containment are not fully efficient on TR4; and alternative options TR4 tolerant varieties- are still at the evaluation stage. The social consequences of Fusarium wilt can be severe: bananas are an important source of food, income, employment, and government revenues in 135 tropical and subtropical countries. Planting material, water, soil particles, tools, footwear and machinery can efficiently disseminate the pathogen. The fungus can survive in soil for more than 20 years. The pathogen can survive as clamydospores in absence of a host. Proximity to banana roots induces chlamydospore germination. Banana infection occurs as response to primary and secondary root exudates. The disease has a long latent period, and there is no symptomatic differences among races. Early detection of symptoms in the field and fast laboratory diagnostic are essential for eradication or containment of outbreak.

The main pathways for transmission of TR4 are infected living or dead host plants, soil from infected fields, carried out of the field by people machinery and animals or mechanically as contaminants on tools. Soil movement with transport and irrigation water, drainage, or other water fluvial could spread secondary inoculum. Highest risk of dispersal is via propagation material that has historically been the main dispersal mechanism. Introduction of TR4 in any country could result in substitution of most popular banana genotypes by others of lower acceptance. It will also lead to introduction of new banana production methods requiring different and more costly cropping practices.
Risk management is carried out via application of firstly, phytosanitary measures to prevent the entry of TR4 into the country and eradication-confinement or suppression-contention measures in case of an incursion. The first step is an absolute prohibition of the entry of plant or plant parts from sites where TR4 is present. At entry points, TR4 presence can be detected by carrying out inspection of plants with wilt and vessel-necrosis symptoms. The plants should be seized and sent to a diagnostic laboratory. Once the presence of any organism of the TR4 complex is confirmed, the material should be confiscated and immediately destroyed. Molecular based methods such as Polymerase chain reaction, Amplified fragment length polymorphism, and Sequencing of ITS region are used to diagnose TR4 in infected plants.
The disease is prevented in several ways, which involve national legislation and biosecurity measures. TR4 should be included in the national list of quarantine pests and of obligatory declaration. Prohibition in importation of Musa plants, plantlet, or other hosts from countries where TR4 is present. Imports of Musa germplasm or of plants for propagation should use the route of intermediate quarantine stations. Those materials should be adequately indexed and identified as free of TR4. The capacity-building and sensitization campaigns among personnel that in the line of duty, visit fields in countries where TR4 is present. This should include measures to take after field visits to prevent transfer of soil or plant parts in clothes, shoes, and/or work equipment.
The disease is managed through phytosanitary based quarantine measures and limitation of area access, use of soil fumigants, sanitation of infected and neighbouring plants, use of soil fumigants and replanting. The production of a certified healthy planting material program accessible to growers. Crop rotation with Fusarium wilt non-host plants has been used to reduce Fusarium oxysporum f. sp. cubense population in the soil. Nutrition is used to minimize the development of the disease through application of nitrate (NO3-) based fertilizers. High phosphorus content in soil reduces Fusarium wilt incidence. High calcium oxide (CaO) content reduces chlamydospores germination. A reduction in iron reduces chlamydospore germination.
GLOBALG.A.P. on TR4 awareness
GLOBALG.A.P. and the World Banana Forum developed a call to action to save the banana from the threats of Tropical Race 4. It is a global initiative to raise awareness and to focus attention on six key areas in which stakeholders can act to prevent TR4 from destroying banana plantations around the globe. The GLOBALG.A.P. save the banana call to action consists of six commitments:
1. To raise awareness of the devastating effects of TR4 and risks of spreading
GLOBALG.A.P. recognizes that there is a need to raise awareness amongst a wide range of stakeholders about the high risks of TR4 and the way it spreads, via contaminated soil particles in addition to infected planting material. The target group includes banana producers and their workers, local communities, public authorities, and everyone involved in the banana value chain, such as shippers, traders and retailers. Awareness raising measures must help these stakeholders understand both the risks and the necessary prevention/quarantine measures wherever Cavendish bananas or other susceptible cultivars and/or host plants are cultivated.
2. To work together with stakeholders
GLOBAL G.A.P. recognizes that TR4 is a shared global challenge. A multi-stakeholder approach is essential. The collaboration of all stakeholders is important. We will identify ways in which our organization can become part of the growing global commitment of stakeholders in the production of bananas (producers, supply chain actors, research institutions, governments and international organizations) to prevent further spreading of the TR4 disease and to protect the sector. The organization hereby recognize the importance of a global network of collaboration on TR4 that could be facilitated by the World Banana Forum (WBF), hosted in the Food and Agriculture Organization of the United Nations (FAO). Providing a necessary permanent space of assembly, the WBF would act as a neutral convener for participants involved in the global banana supply-chain to promote an action consensus on activities to prevent TR4.

3. To promote risk management tools
The organization recognizes the need to promote risk management tools that help banana producers implement preventive biosecurity measures on their farms, and identify and control TR4, to promote regional and national contingency plans, formulated by regional phytosanitary authorities (such as OIRSA) and governments of several important banana exporting countries. Such tools should enable banana producers and other supply chain stakeholders (such as shippers, ports, local communities, certifying bodies, public authorities) to implement the recommendations of these and other institutions (such as the FAO, the Government of Queensland, the banana research network MUSALAC, the World Banana Forum and others) and make joint efforts to prevent further spreading of TR4.
4. To Support the adoption of appropriate early warning systems
GLOBALG.A.P. recognizes that the early detection of TR4 is crucial in the prevention of further spreading. They support the adoption of appropriate surveillance methods and early warning systems based on rapid diagnostic techniques of the disease and risk assessments. Small farmers and banana workers, who are daily present in banana plantations, are among the first persons to detect suspect cases and symptoms of possible diseases if properly trained and can play an important role in prevention strategies. Local authorities and governments in banana producing regions and phytosanitary laboratories should also be prepared and implement surveillance methods, build up diagnostic capacity, elaborate early warning systems and adequate quarantine legislation.
5. To develop training programs
GLOBALG.A.P. agrees that small farmers and banana plantation workers should receive training on the nature, risks, characteristics, and symptoms of TR4. Training materials for different target groups need to be developed in relevant formats and should include “train the trainer” modules and tool boxes in particular for small and medium-sized banana producers and organisations. Training materials should focus on awareness raising, training in surveillance, detection and biosecurity measures. They also agree that a mobilisation of funds is necessary to implement training, teaching and education at all levels.

6. To Promote research
The TR4 threat is a wake-up call for all stakeholders of the banana sector. As GLOBALG.A.P. we recognize that in order to find long term solutions on the specific challenge of TR4, and in general terms, to promote a more sustainable banana, research is needed in a variety of fields. Innovation is badly needed to build a resilient banana sector that is ready to face actual and future challenges. Public and private stakeholders need to work together to look for innovative and structural ways to raise funding to make this transition possible.
Bolton Kudzai Kakava is a Plant Pathologist/Agronomist/Farm Assurer and can be contacted on +263779579803 or email him at boltonkudzi@gmail.com.