TR4: will history repeat itself?

Boudy van Schagen Friday, 07 June 2013

If you believe that history will repeat itself unless we learn from it, then you may be interested in a historical review of the introduction and spread of banana pests and pathogens on the African continent. It provides some revealing insights into how most of today’s most damaging pests and pathogens were unwittingly introduced into Africa with imported planting material. Against a backdrop of increasing travel movements, it urges renewed vigilance to prevent more pathogens from creeping in.

Bananas are not native to Africa and, with a few exceptions, neither are their all-too-familiar pests and diseases. The banana weevil, black leaf streak, bunchy top and Fusarium wilt (race 1), to name only the more notorious ones, came in as excess luggage in cultivars. The rest is history, as the saying goes. They are now well established across many parts of banana-growing Africa, and cause untold damage. In Burundi, where I live, banana diseases such as Xanthomonas wilt and bunchy top pose a serious threat to the livelihoods of farmers. Bunchy top has even made it to the capital, Bujumbura. This picture of a plant with bunchy top was taken in a private garden.

But looming large on the horizon is a new threat to African banana farmers: the tropical race 4 variant of Fusarium wilt (better known as TR4). TR4 was thrust into the limelight when it destroyed commercial Cavendish plantations in Malaysia and Indonesia in 1988. The killer fungus went viral (sorry) and spread to banana production areas in four more countries, including China. Once introduced, TR4 spreads rapidly with infected planting material, on contaminated tools, and in contaminated water and soil.

Halting the international movement of infected planting material is the crux of keeping this violent offender out of Africa. And yet, history has shown that it is difficult to stop pathogens from spreading within countries and across borders. Given the ease of modern air travel, and more migration from Asia to Africa, the illegal immigration of TR4 is not unthinkable. It need not spell disaster, however. In Australia, for example, strict quarantine regulations have prevented the spread of TR4 from the Northern Territory to the country’s main banana-producing regions.

Of course, the ideal scenario is if TR4 doesn’t make it to Africa in the first place. History will tell whether it does. In the meantime, strengthened border controls and phytosanitary inspections should go a long way to prevent its introduction.