Insight on the inside Phloem-based whitefly resistance in tomato

The vasculature of a plant consists of twomajor systems, the phloem and the xylem. The water and minerals taken up by theroots are transported to the shoot through the xylem, while the compoundsproduced by the plant itself are distributed throughout the plant via thephloem. The phloem lays buried within the plant under multiple cell layers andis thereby protected against most insects, except for the phloem-feedingHemiptera which include whiteflies and aphids. Whiteflies (Bemisia tabaci),and the viruses they vector, are a major issue for tomato (Solanumlycopersicum) cultivation and their infestations are therefore frequentlyprevented by pesticide application. A more sustainable solution can be soughtin the defence mechanisms of wild relatives of crop species, like the toxic andrepellent specialised metabolites in the glandular trichomes of some tomatospecies. We had indications that another resistance mechanism based onspecialised metabolites might be present in the phloem of wild tomato. The aim ofthis thesis was therefore to explore the tomato phloem as a site for insectresistance through the identification of phloem-based metabolites that affectthe proliferation of B. tabaci. To this end, we assessed (1) thedevelopmental success of B. tabaci on a set of wild and cultivatedtomato plants as a measure of resistance in the host plants and (2) the naturalvariation in phloem-based specialised metabolites in the wild and cultivatedtomato plants, to (3) link the specialised metabolites in the phloem to theresistance phenotype.