Discussion:
We demonstrate here that fruit development (and thus by extension, seed production) in an annual plant species is prioritised at the expense of vegetative tissues under water stress through relatively greater xylem resistance to cavitation in those tissues supplying water to fruit. We found that the xylem of vegetative tissues cavitated early during drought, while the loss of xylem function in the main stem and the peduncle occurred much later. These cavitation resistant tissues provided a xylem pathway that prioritized water supply to fruit from other plant parts even when the plant is fully disconnected from a soil water source. The prioritisation of water supply to reproduction in tomato means that unlike observations in perennial plants, the fruit of tomato behaves as a hydraulic parasite upon the vegetative body.