Banana, disease resistance, fungicides, sustainability, food crops, third world
Banana agriculture is in urgent need of new varieties with improved characteristics. Over the past decades, bananas have become increasingly vulnerable to some devastating diseases and pests. The most important one is called Black Sigatoka caused by a fungus which blackens parts of the leaves, thereby impeding photosynthesis and causing fruit losses of 50% or more. It has spread to most banana-growing regions across the world. Today, Black Sigatoka infestations are combated through the heavy use of fungicides. Since the 1990s, a second disease is endangering banana cultivation which is caused by a Fusarium soil fungus, called Tropical Race Four. Currently, this disease is restricted to some parts of Asia. However, once it will spread, the consequences will be even more devastating than for Black Sigatoka since there are no chemicals that can effectively control Fusarium. In the 1950s, a related Fusarium strain caused an end to the global cultivation and export of Gros Michel, the most popular banana variety of that time. Besides these fungal diseases, bananas may face one or more additional challenges, depending on where they are grown. For example, banana cultivation may suffer from drought or from some other diseases, caused by insects, roundworms, bacteria or viruses.
With 125 million tonnes annually, banana is the No. 1 fresh fruit source in the world. It is grown in more than 120 countries, primarily in the tropical regions of Africa, Asia, and Latin America. 85% of all produced banana is consumed locally. Indeed, for millions of people, mostly smallholder subsistence farmers, banana is a principal component of their daily energy intake. In Eastern Africa, banana provides for up to 30% of calorie intake and is the most important staple food for more than 70 million people. In Latin America, Asia and Western Africa, many farmers are dependent on the production of export bananas as a source of income. In countries like Ecuador, Panama and Costa Rica, bananas represent 7-10% of the total national export value. Bananas are therefore critical both to global food security and farmer income in developing countries. In addition, there is a major environmental and cost issue. On average, one hectare of commercial banana plantation is sprayed with 1000 Euro worth of fungicides per year. This means that 15-20% of the retail price in importing countries goes to costs for fungal control. Such expensive measures are unavailable to small-holder farmers, who are therefore most strongly affected by the Sigatoka disease.
In a previous project from 1996 to 2001, new banana varieties were introduced in the Kagera district of Tanzania through a Belgian aid project. The project had an impact on a million people in that country, increasing farmer income from bananas six-fold in five years time. The success of this program was recognized by the United Nations through a Cooperation Excellence Award. Spurred by this success, our new project aims to deliver a structured and long-lasting stimulus to banana research and international development. In this project, we will utilize the world collection of more than 1000 banana varieties, that has been established under the auspices of the FAO and that is maintained in our laboratories. The major goal of this collection has been to preserve banana biodiversity for mankind and to function as a biodiversity repository and distribution centre. Until now, more than 80,000 samples have been supplied worldwide to 355 locations in 100 countries. Projects like the one in Tanzania have benefited directly from the existence of this collection. In this new project, we want to lift the Banana Biodiversity Collection one level higher: from genetic preservation to genetic improvement. Genetic improvement aims at the creation of new types of bananas that combine beneficial traits from different varieties, either by breeding or, in the case of sterile banana types such as Cavendish and most plantains, through genetic engineering. For this purpose, genetic maps of the most important varieties need to be established. In the past two years, genomic markers and sequencing techniques have advanced tremendously. As a result, making genetic maps of different banana varieties carrying the most desirable traits has become feasible. With these genetic maps, researchers around the world can start improving bananas for a diverse set of traits.
Resistance against fungal diseases such as Black Sigatoka and Fusarium are the most needed features to be introduced in a wide variety of bananas. But the same genetic mapping platform can also be used for other important traits, such as drought tolerance, insect resistance (banana weevil) or resistance against roundworms, bacteria or viruses. Hence, the availability of genetic maps for most important banana varieties will deliver a new dimension to the Banana Biodiversity Collection. Because it is a generic tool, it will be of use to banana scientists and breeders in a wide range of research areas and it will ultimately bring better bananas varieties to farmers in developing countries.
Natural resistance against Black Sigatoka has been found in specific banana varieties that are present in the Banana Biodiversity Collection.
Genetic maps for important banana varieties and identification of the chromosomic regions that contain the resistance genes against Black Sigatoka.