The Genetics of Trichome Density and Resistance to Two-Spotted Spider Mites in Tomatoes from the Galapagos Islands

In tomato, pest resistance sources have been identified among wild accessions. Previous studies demonstrate a role for acyl sugars produced by type IV glandular trichomes from wild relatives of the cultivated tomato in providing resistance to a number of insect pests. One of these wild species, Solanum galapagense, which is endemic to the Galapagos Islands of Ecuador, shows a high density of type IV glandular trichomes. This study aimed to assess resistance to two-spotted spider mites (Tetranychus urticae) in tomato clones, previously selected from an F2 population derived from crosses of S. galapagense and a commercial variety.  Directional selection was practiced for high and low trichome density and a tail-mapping approach was used to identify QTLs associated with resistance. Resistance to two-spotted spider mites was assessed based on insect movement behavior and proved to be negatively correlated with the density of type IV glandular trichomes (P =3.2E-08; R² = 0.658). QTLs were identified for two-spotted spider mite resistance located on chromosomes 2, 3 and 10. Two of these QTL are also associated with the density of type IV trichomes. Thus inheritance of trichome density and resistance appears to be genetically simple, with 2-3 loci contributing.