The banana has been severely affected by fungal diseases that can only be combated by using more and more plant protection products. In the last century, the much-loved Gros Michel banana variety was wiped out as a result of Panama disease. But now the replacement variety Cavendish – available in every supermarket – is at risk. At his inauguration as professor by special appointment for Tropical Phytopathology at Wageningen University & Research on 21 September, Professor Gert Kema reveals what it will take to save the banana.
The Cavendish export banana does well in all types of soil and for years showed little susceptibility to Panama disease. For this reason, major banana producers planted the Cavendish en masse on the defunct Gros Michel plantations. The 'agronomic miracle,' as Cavendish has been dubbed, came to dominate the international market and has partly supplanted local varieties in India and East Africa, says Professor Kema. ‘Moreover, retailers keep the kilo price to a minimum because bananas generate top turnovers in supermarkets. They are money machines, similar to cotton T-shirts. As with other “orphan crops,” monetary investment has lagged behind in the financially thriving banana industry. No money has been put into basic scientific research. Now we know that was the wrong decision.’
Return of Panama disease
Panama disease is caused by a Fusarium fungus, which has now developed an extremely virulent strain known as TR4 (Tropical Race 4), with disastrous consequences. What’s more, there are no seeds banks with propagating material for new varieties to replace the Cavendish. ‘We are back to square one,’ concludes the professor. ‘Cavendish has one major drawback: there is no genetic variation. This means that the bananas of the big brands and fair-trade bananas are genetically identical. They are clones grown in extreme monocultures and are therefore all equally sensitive to fungal diseases,’ he says in his inaugural address Tropical phytopathology – dragging orphan crops into the spotlight.
‘At the same time, the major producers are focusing exclusively on preserving the Cavendish and the practical knowledge we have of it,’ criticises Professor Kema. ‘Panama disease was identified in the Cavendish in Taiwan as early as 1960, but only when we demonstrated that the TR4 fungus variant had surfaced in Jordan, and later in Lebanon, Pakistan, Laos and Mozambique, did the sector wake up to the problem and suddenly start calling for emergency measures. In addition, only 15% of the harvest is destined for export, while the remaining production is sold on the local market. Millions of farmers are dependent on a good harvest, and this harvest is threatened by the introduction of the TR4 fungus strain through new Cavendish planting in “clean” areas by conservative market players.’
Saving the banana
Our ability to control the TR4 fungal strain relies on having genetic knowledge of both the banana varieties and the fungus. Professor Kema's research group has since catalogued a thousand strains of Fusarium and has been able to map out a family tree of the fungus. In this way, they can see where the fungus originally spread from and draw parallels with human migrations.
The group is also concentrating on breeding programmes based on varieties of wild bananas. ‘This is because ensuring genetic variation is the key to tackling most problems in bananas. Genetic variation also means more choice for consumers,’ says Professor Kema. It will take no fewer than ten years to produce new varieties. In addition, the Wageningen professor hopes to collaborate with partners from the business world on the science so that solutions will actually find applications in the banana economy. But the research group is also seeking contact with small-scale banana growers in order to investigate their questions, dilemmas, choice of varieties and access to the market. This should also mean that in future they will be able to choose between several resistant banana varieties for the market for food, fruit and fibres.
Professor Kema's special chair is funded by the Dioraphte Foundation and hosted by the Laboratory of Phytopathology headed by Professor Bart Thomma.