Developing Viral Disease Resistance in Tomato

A major viral disease of tomato caused by a complex of viruses called Tospovirus has been found in all tomato producing regions of Brazil. It can totally wipe out young tomato seedlings and the only solution is to breed for resistance against the virus. A resistant gene Sw-5 against the virus was discovered by Eric Campos Dianese of the University of Brazil under the supervision of Maria Esther de Noronha Foresca. The presence of the gene in tomato plants was highly correlated to resistance against the virus. Studies also showed that Tospovirus forms a complex of virus species with different characteristics.

Molecular markers for the gene have previously been identified which have been used in rapid introgression of the Sw-5 gene into commercial varieties. These markers however are located near the gene and can be separated during crossing work. With the discovery of the viral resistance gene Sw-5, new markers derived from the Sw-5 gene itself were developed and are more ideal in differentiating susceptible and resistant plants.

According to Leonardo Boiteus, the coordinator of tomato breeding program at Embrapa Vegetables, the new marker ensures the maintenance of viral resistance in a plant since the Sw-5 gene is dominant and can be expressed in heterozygous state. He added that, "the system can be used for any type of tomato which is important for seed companies that focus on developing new tomato hybrids."

See the news article in Portuguese at http://www.cnph.embrapa.br/paginas/imprensa/releases/vira_cabeca.html