Combining transgenic and natural resistance to obtain broad resistance to tospovirus infection in tomato (Lycopersicon esculentum mill)

This study was undertaken to develop tomato plants with broad resistance to tospoviruses which are a major limiting factor to tomato production worldwide. A nontransgenic tomato line Stevens-Rodale (S-R), six transgenic tomato lines expressing the nucleocapsid (N) protein gene of the lettuce isolate of tomato spotted wilt virus (TSWV-BL), and progeny of the crosses between S-R and three of the transgenic lines homozygous for the N gene were evaluated for their resistance to tospovirus infection in greenhouse inoculation tests. S-R has the Sw-5 gene that confers resistance to several TSWV isolates. The six transgenic lines showed high levels of resistance when inoculated with either TSWV-BL or a tomato isolate from Hawaii (TSWV-H). However, these same plants were highly susceptible to the Brazilian isolate of groundnut ringspot virus (GRSV-BR). Plants with the Sw-5 gene were resistant to TSWV-BL and GRSV-BR, but were susceptible to TSWV-H. When inoculated with any of the three viruses, the F-1 progeny of the crosses exhibited a susceptible, tolerant, or resistant phenotype with a higher proportion of the plants being either tolerant or resistant. When F-2 progeny from F-1 resistant plants of each cross were inoculated with any of the three viruses, a higher proportion of tolerant and resistant plants was observed compared to the F-1 progeny. Our results show the potential to obtain broad resistance to tospoviruses by combining transgenic and natural resistance in a single plant.