The ratio of trichomes to stomata is associated with water use efficiency in Solanum lycopersicum (tomato)

Trichomes are specialised structures that originate from the aerial epidermis of plants, and play key roles in the interaction between the plant and the environment. In this study we investigated the trichome phenotypes of four lines selected from the Solanum lycopersicum x Solanum pennellii introgression line (IL) population for differences in trichome density, and their impact on plant performance under water-deficit conditions. We performed comparative analyses at morphological and photosynthetic levels of plants grown under well-watered (WW) and also under water-deficit (WD) conditions in the field. Under WD conditions, we observed higher trichome density in ILs 11-3 and 4-1, and lower stomatal size in IL 4-1 compared with plants grown under WW conditions. The intrinsic water use efficiency (WUEi) was higher under WD conditions in IL 11-3, and the plant-level water use efficiency (WUEb) was also higher in IL 11-3 and in M82 for WD plants. The ratio of trichomes to stomata (T/S) was positively correlated with WUEi and WUEb, indicating an important role for both trichomes and stomata in drought tolerance in tomato, and offering a promising way to select for improved water use efficiency of major crops.