Water-use efficiency and drought tolerance in Lycopersicon esculentum and L. pennellii and their F sub 2 crosses

In growth chamber experiments the authors compared the water-use efficiency (WUE) and drought tolerance (DT - retention of dry mass vegetative yield when droughted) of the drought intolerant common tomato, L. esculentum and the ostensibly drought tolerant tomato, L. pennellii. Drought treatment was imposed as two severe episodes of drought, each episode lasting until all leaves on the plant were silted, with a period of recovery between treatments. They measured up to 20 performance attributes to WUE and DT, including: root:shoot ratio, leaf internal CO2/ambient CO2, {delta}{sup 13}C, leaf photosynthetic rate, specific leaf mass, leaf water potential, leaf osmotic potential, and stomatal density. Water-use efficiency is negatively correlated with drought tolerance; drought tolerance is positively correlated with plants' ability to increase WUE under stress. Few other attributes are correlated with drought tolerance, and some are conspicuous by their absence. They find evidence for substantial genetic linkage among attributes that confer drought tolerance; and interplant rankings in drought tolerance depend strongly upon the type of drought stress experienced (episodic vs. continuous).