Tropical Race 4 of Panama disease (TR4 of Fusarium wilt) is spreading to new localities in Asia and the Middle East. It is feared to be just a matter of time before it spreads from northern Mozambique, where it is currently present, into other African countries. The first global campaign to address the banana disease has just been launched by the United Nations’ Food and Agriculture Organisation (FAO) and its partners. Previous campaigns aimed at the disease had a continent-specific focus.Fazil Dusunceli, plant pathologist at the FAO, calls Fusarium TR4, which severely affects the Cavendish banana cultivar, the most destructive disease that can affect bananas. There is no effective chemical to kill the fungus and unlike when Fusarium wilt decimated Gros Michel bananas, the international banana export industry has no alternative to the Cavendish. Globally, the Cavendish makes up around 50% of all bananas produced and is worth $36 billion. In total, more Cavendish is grown and consumed in-country than is exported.
The first incidences of Fusarium TR4 in Laos and Vietnam have just been reported after being confined to Indonesia, Malaysia, the Philippines, mainland China and Taiwan for more than thirty years. Prof Altus Viljoen of Stellenbosch University and colleagues recently wrote in the Plant Disease journal: “Cavendish production is now being expanded in Asia to Laos, Myanmar and Vietnam, where local varieties still dominate the market. This is due to an increase in Cavendish banana consumption and a decline in areas of production caused by Foc [Fusarium oxysporum f. sp. cubense (Foc)] TR4 in China. The expansion of Cavendish production in Southeast Asia, however, has increased the risk of Foc TR4 being introduced into new countries.”
Great concern about Fusarium TR4 in Africa
In Africa, Fusarium TR4 only occurs in Nampula Province in the north of Mozambique, a relatively dry area, but plant pathologists regard it as a significant threat to the livelihoods of millions of people in East and Central Africa. The fungus can remain present in soil for decades.
“Fusarium TR4 is very serious on the Mozambican farms where it occurs and consequently there is great concern that it could spread both within Mozambique and to neighbouring countries, like South Africa. To be honest, I think it’s a matter of time before the disease also occurs in other parts of Africa because the necessary preventative measures weren’t implemented,” says Prof Altus Viljoen of the Department of Plant Pathology at the University of Stellenbosch, a leading banana disease expert who positively identified the disease in Mozambique in 2013.
“The disease has caused tremendous damage in Mozambique and has killed approximately a million plants on one farm, about 15,000 plants a week at the height of the epidemic,” he continues. “Once the disease has been established, one can’t get rid of it.”
Somaclonal Cavendish variants with TR4 tolerance trialled in southern Africa
Currently the only option are somaclonal Cavendish variants bred in Taiwan, which have a higher degree of tolerance but not total immunity to the TR4 Fusarium. The drawback is that it’s uncertain how well these plants will fare in subtropical areas, like the banana-producing regions of South Africa. Furthermore, there are uncertainties regarding their yield as well as their agronomic adaptability and suitability for processing and transport, therefore these clones are currently being trialled in Mozambique, South Africa and Zimbabwe.
These Taiwanese Cavendish clones are now widely planted on the affected farms in northern Mozambique but according to Prof Viljoen, it’s as yet unsure whether their yield will remain constant over the coming number of seasons.
“Basically Africa is extremely vulnerable to Fusarium TR4 because of the nature of its production systems. If you have large scale Cavendish production, like a thousand hectares you can probably cut 40 hectares out where the disease came in initially. For small growers with a quarter of a hectare, half a hectare - there is just no way you can tell them: don’t move there. The second aspect is the production system – in large scale systems they use clean planting material produced in laboratories through tissue culture. Small growers cannot afford that. They have to take suckers from specific areas. If these plants have been in contact with a fungus they quickly spread it to new areas.”
For more information:
Prof Altus Viljoen
Department of Plant Pathology, University of Stellenbosch
Tel: +27 21 808 4797
Email: altus@sun.ac.za