Insight on the inside Phloem-based whitefly resistance in tomato

The vasculature of a plant consists of two major systems, the phloem and the xylem. The water and minerals taken up by the roots are transported to the shoot through the xylem, while the compounds produced by the plant itself are distributed throughout the plant via the phloem. The phloem lays buried within the plant under multiple cell layers and is thereby protected against most insects, except for the phloem-feeding Hemiptera which include whiteflies and aphids. Whiteflies (Bemisia tabaci), and the viruses they vector, are a major issue for tomato (Solanum lycopersicum) cultivation and their infestations are therefore frequently prevented by pesticide application. A more sustainable solution can be sought in the defence mechanisms of wild relatives of crop species, like the toxic and repellent specialised metabolites in the glandular trichomes of some tomato species. We had indications that another resistance mechanism based on specialised metabolites might be present in the phloem of wild tomato. The aim of this thesis was therefore to explore the tomato phloem as a site for insect resistance through the identification of phloem-based metabolites that affect the proliferation of B. tabaci. To this end, we assessed (1) the developmental success of B. tabaci on a set of wild and cultivated tomato plants as a measure of resistance in the host plants and (2) the natural variation in phloem-based specialised metabolites in the wild and cultivated tomato plants, to (3) link the specialised metabolites in the phloem to the resistance phenotype.