Science - August 8, 2012

Kema gets down to business to make disease-resistant bananas

Wageningen phytopathologist Gert Kema and French researchers published the banana genome sequence in Nature in July. The wild banana (Musa acuminate) has genes which are resistant to the dreaded Panama disease. Kema will set up his own company to track down these genes.

Gert Kema
The bananas which we eat - the Cavendish variety - are grown in monoculture cultivation, which is becoming more susceptible to fungi. In particular, the soil fungus Fusarium oxysporum, for which Kema is an expert in, affects banana plantations all over the world. As a result, large quantities of herbicides are used, and there is now a Fusarium strain which the Cavendish banana is not resistant to: the Tropical Race 4 has shown up in Southeast Asia. The genome researchers discovered to their surprise that the wild variety of the banana is resistant to the TR4. 
'This wild variety is not edible,' says Kema. 'Unlike the Cavendish, which is sterile, the wild variety contains many seeds. Since we now know the genome sequence of this wild variety, we have the basic reference for breeding a resistant banana for consumption.' 
Are you going to cross the wild variety and then search for the genes which are responsible for the resistance? 
'We want to produce about a hundred new plants from the Musa and then determine which ones are resistant, and afterwards look for the genes responsible for this resistance against Fusarium. We will then introduce these genes into commercial varieties.' 
Who will finance the research? 
'Setting up a company appears to be the best way to get hold of money needed for the research, which is what I'm doing. I have been asking research fund providers and companies in the past five years whether they would finance research into developing resistant banana varieties. Public funding is hard to come by, and even banana giants such as Chiquita and Del Monte have less money for research than what most people think. But now I've found investors interested in developing resistant banana varieties. These are mainly private investors or philanthropists. I hope to link their investment in my company to public funds. The company will have three owners, the other two being an Australian professor and a Philippine banana company.' 
Are one or two genes sufficient to make the banana resistant? In the case of the potato blight fungus Phytophthora, mutations continuously break down the disease resistance of potatoes.  
'Unlike Phytophthora, Fusarium does not reproduce itself sexually. As such, the mutations which can occur in this enemy of the banana will be much fewer. Therefore, the resistance genes used in banana cultivation can provide a much longer protection. This can also be seen in practice. In the previous century, the former food banana Gros Michel was wiped out by Fusarium in the 1950's. Then came the discovery that the Cavendish was resistant against this disease. This is still the case in Latin America. The use of resistant genes is therefore a sustainable solution.' 
Don't the French researchers who unravelled the genome together with you want to participate in the company? 
'France has its own research programme to develop a resistant variety; it's trying to reproduce the resistance by crossing the wild variety. This classical method will certainly take ten years before producing results. I've decided to use another method. I will develop a cisgenetic banana and introduce specific resistance genes from the wild banana into commercial varieties. This approach is more precise and faster.'
Two years ago, Kema developed a quick DNA test to detect the disease pathogen in banana plantations.

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