www.czu.cz ; www.raupp.info

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 found these same two genes,
which provide resistance against a certain fungus, in several wild tomato
species, October 2004 .

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

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.

Kruijt also demonstrated that DNA exchange between the various Cf genes has
led to a new Cf resistance gene.

Cladosporium fulvum causes a fungal disease in tomato plants. Wild tomato
species contain many resistance genes against this fungus. 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. This
'scorched earth tactic' ensures that the fungus cannot infect the rest of
the plant.

The research was funded by the Netherlands Organisation for Scientific
Research.

[www.eurekalert.org]

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