Mapping of Traits Associated with Water-Use Efficiency in Near-Isogenic Lines Derived from Wild Tomato (Solanum habrochaites)

Increasingly limited fresh-water resources and global climate change threaten agricultural production systems worldwide.  Breeding for increased water-use efficiency (WUE) and tolerance to water stress can improve the sustainability of a cropping system by requiring less water for a given level of yield. WUE is prohibitively difficult to measure directly in field settings but carbon isotope discrimination (Δ¹³C), the ratio of ¹³C:¹²C measured in mature leaf samples, is correlated with WUE.  Wild tomato (Solanum habrochaites) exhibits tolerance to abiotic stresses and quickly closes its stomata during rapid-onset water stress caused by root chilling.  This trait is controlled by a major QTL (stm9) on the short arm of chromosome 9.  To determine if other traits associated with water stress tolerance map to this region, a set of chromosome 9 sub-near-isogenic lines (NILs) derived from S. habrochaites were evaluated for multiple traits in replicated field experiments under restricted irrigation in 2012 and 2013.  Traits measured included Δ¹³C, specific leaf area, leaf phenolic content, fruit yield, and plant biomass.  Traits associated with WUE segregated within an introgressed region from S. habrochaites that also contains stm9.  QTLs for Δ¹³C were conferred by alleles from both the cultivated parent and S. habrochaites.  Research and data analyses investigating the relationships among traits associated with WUE and yield under restricted irrigation is ongoing.  Our research will aid tomato breeding efforts to address challenges imposed by limited fresh-water.