Tomatoes: science pins down natural defence gene

Related tags Tomato

Identifying the gene responsible for natural defense mechanism in
tomatoes could save costs for tomato producers and ultimately food
processors using this common food ingredient.

Dutch researcher Marco Kruijt has discovered two resistance genes that were probably present in an ancestral tomato species, prior to the evolution of modern tomato species.

The phytopathologist, working out of the Netherlands Organisation for Scientific Research, found these same two genes, which provide resistance against the Cladosporium fulvum fungal disease, in several wild tomato species.

In Europe, 8.5 million tons of tomatoes are cultivated annually with 1.5 million tons sold directly to the consumer and 7 million are processed for products such as ketchup and sauces.

Tomatoes are attracting increasing interest from the food industry for their health-promoting characteristics, notably the health-boosting antioxidant lycopene.

Market analysts Frost & Sullivant predict the lycopene market will exhibit growth rates at over 100 per cent. The report values the ingredient at $34 million (€27.6m) in 2003.

While the food industry has enjoyed reduced prices for tomatoes due to over production that started in 1999 to 2000, this latest Dutch research could offer savings to the farmer, despite the surplus production.

Growing competition from China - now the third largest producer although 10 years ago a small player - has also diluted prices. And imminent competition from producers in an enlarged Europe will also change the landscape and make for pressing times for the industry.

Contracts today are in the $50 to $60 zone a tonne for the EU and the US, but are coming in at about $30 a tonne from China.

"Prices for tomatoes only started to rise some 15 months ago," a spokesperson for AMITOM, the Mediterranean International Association of the Tomato Processing recently told FoodNavigator.com.

"Many companies have suffered in Europe, particularly smaller producers such as France, and we are still feeling the impact of overproduction and the impact of emerging markets such as China, Chile and Turkey," he added.

California is currently the largest tomato processor, followed by Italy and the new kid on the top block, China.

Tomatoes resistant to the fungus Cladosporium fulvum possess the so-called Cf resistance genes. For the Dutch tomato study Kruijt​ investigated the evolution of these genes in wild tomato species.

The researcher reports that he managed to demonstrate that a number of these Cf resistance genes were already present in an ancestral tomato species.

"In all probability, the fungus C. fulvum was already a pathogen of this ancestral tomato species, and therefore the resistance genes Cf-4 and Cf-9 have been retained in the various modern wild tomato species,"​ claims Kruijt.

The researcher also discovered that wild plants on which the Peruvian or berry tomatoes grow contain not one but three resistance genes, all of which recognise the same fungal factor. These three genes are the result of a series of changes that have led to complete pieces of DNA being duplicated.

The researcher adds that in particular, the Cf-9 gene from the wild berry tomato Lycopersicon pimpinellifolium​ is frequently used in commercial tomato varieties. Each of the Cf resistance genes recognises a different product from the fungus and this recognition in the tomato leaf causes a number of cells around the fungus to die.

In another gene study, scientists at Cornell University, the Boyce Thompson Institute and Colorado State University announced​ earlier this month that they are working to sequence a portion of the gene-rich regions of 12 tomato chromosomes.

The move is part of an international effort to develop a reference genome sequence for the plant family Solanaceae, to which the tomato belongs along with aubergines, paprika and the potato.Scientists will sequence 400,000 bacterial artificial chromosomes (BAC) reads end assembled from the tomato (Solanum lycopersicon) genome.

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