Developing Capsicum and tomato cultivars with resistance to Tospoviruses in Australia
Persley DM1, Sharman M1, McGrath D2, Garland S2
1Cooperative Research Centre for Tropical Plant Protection, St Lucia, Australia 4072.
2Department of Primary Industries and Fisheries, Bowen, Australia 4805
Correspondence: denis.persley@dpi.qld.gov.au
Capsicum (pepper) crops in Queensland, Australia can be seriously affected by both Tomato spotted wilt virus (TSWV) and Capsicum chlorosis virus (CaCV). The latter virus, first described from Australia, is a member of the serogroup IV or Watermelon silver mottle virus serogroup (McMichael et al.2002). Although useful resistance to TSWV has not been found in Capsicum annuum, resistance expressed as a hypersensitive response, and controlled by the dominant gene Tsw, has been found in several C. chinense accessions, including PI 152225 and PI 159236, and introgressed into C. annuum lines (Roggero P et al. 2001. Proceedings of the 7th International Symposium on Thysanoptera, University of Reggio Calabria, Italy). The Tsw gene is not effective against CaCV (McMichael L et al. 2002. Australasian Plant Pathology 31:231¨C239). When 38 C. chinense accessions from the USDA/University of Georgia collection were screened by sap inoculation with CaCV, one line (PI 290972) developed a hypersensitive response on inoculated leaves with premature leaf abscission and no detectable virus by ELISA and RT-PCR assays of new growth leaves. Six sub-lines of PI 290972 were established by self pollination; all were resistant to CaCV and one was also resistant to TSWV, developing a hypersensitive response following inoculation. Resistance to both CaCV and TSWV was dominant in the F1 generation of crosses between PI 290972 and two bell capsicum lines. This material has now been advanced to a third backcross. Selection efficiency has been enhanced by using a dominant PCR¨Cbased molecular marker to select segregates for CaCV resistance. Results were confirmed by manual inoculation of backcross populations which supported a single dominant gene model for inheritance of the resistance. The Sw-5 gene for TSWV resistance in tomato has been incorporated into elite tropically-adapted lines by backcrossing. Selection efficiency has been improved by the development of a PCR-based marker system that consists of coamplification of a dominant marker representing the Sw-5 gene sequence and a modified cleaved amplified polymorphic sequence (CAPS) marker as a positive control and indicator of genotype (Garland S et al. 2005. Australian Journal of Agricultural Research 56: 285¨C289).
