Marker-assisted Selection for Coupling Phase Resistance to Tomato spotted wilt virus and Phytophthora infestans (Late Blight) in Tomato

Tomato spotted wilt virus (TSWV) and Phytophthora infestans (late blight) in tomato (Solanum lycopersicum) have a worldwide distribution and are known to cause substantial disease damage. Sw-5 (derived from S. peruvianum) and Ph-3 (derived from S. pimpinellifolium) are, respectively, TSWV and late blight resistance genes. These two genes are linked (within 5 cM on several maps) in repulsion phase near the telomere of the long arm on chromosome 9. The tomato lines NC592 (Ph-3) and NC946 (Sw-.5) were crossed to develop an F-2 population and subsequent inbred generations. Marker-assisted selection (MAS) using three polymerase chain reaction-based codominant markers (TG328, TG591, and SCAR421) was used in F-2 progeny with the goal of selecting for homozygous coupling-phase recombinant lines. From 1152 F-2 plants, 11 were identified with potential recombination events between Ph-3 and Sw-5; of those, three were male sterile (ms-10). F-3 progeny were generated from the remaining eight F-2 recombinants, and resistance to both pathogens, or Ph-3 and Sw-5 in coupling phase, was confirmed in three of those. Recombination was suppressed fivefold in our F-2 population to 1.11 cM between genes when compared with published maps of the same region. However, MAS was an efficient tool for selecting the desirable recombination events for these two pathogen resistance genes.