Use of introgression lines to determine the ecophysiological basis for changes in water use efficiency and yield in California processing tomatoes

Field and greenhouse studies examined the effects of growth habit and chloroplast presence in leaf veins for their role in increasing agronomic water use efficiency and yields of California modern processing tomato (Solanum lycopersicum L.) cultivars. Five introgression lines (ILs), made with Solanum pennellii Cor. in the genetic background of cultivar M82, differ in genes that map to a region on Chromosome 5, including the SP5G gene (determinate vs. semideterminate (Det vs. SemiDet)) and the obv gene (presence (obscure) vs. absence (clear) of leaf vein chloroplasts (Obs vs. Clr)). The five ILs andM82represented three of the four gene combinations (Det-Clr was unavailable). Det-Obs ILs had less leaf, stem and total aboveground biomass with earlier fruit set and ripening than SemiDet-Clr ILs. By harvest, total fruit biomass was not different among ILs. Photosynthetic rates and stomatal conductance were 4-7% and 13-26% higher, respectively, in Det-Obs ILs than SemiDet-Clr ILs. SemiDet-Obs ILs were intermediate for growth and gas exchange variables. The Det-Obs ILs had lower leaf N concentration and similar chlorophyll content per leaf area (but slightly higher per leaf mass) than SemiDet-Clr ILs. The Obs trait was associated with gains in leaf gas exchange-related traits. This study suggests that a more compact growth habit, less leaf biomass and higher C assimilation capacity per leaf area were relevant traits for the increased yields in cultivars with determinate growth. Developing new introgression libraries would contribute to understanding the multiple trait effects of desirable phenotypes.