Ready for the worst: Mediterranean landraces as a source to improve tolerance to water stress in tomato

Climate change predictions indicate an increase of drought periods, especially in the Mediterranean region. These episodes of water-scarcity will be aggravated by possible reductions in the use of fertilizers, since their availability is expected to lower in next decades. The aim of this work is to assess the effect of water and nutrient stress in a 219 genotypes core collection (CC) of tomato (Solanum lycopersicum L.) using highthroughput techniques, in order to identify the outstanding genotypes. Different classifications of this CC were made based on their growth habit, genetic selection or fruit type. All genotypes were grown under two different cultivation conditions: wellwatered (WW, covering 100% evapotranspiration and nutrient demands) and combined-stress (CS, no water and nutrient application after a month since transplantation). Plant area, leaf morphology, water use efficiency (measured by leaf δ13C isotopic composition and gas exchange), yield, fruit morphology and quality measurements were performed. As expected, plants grown in CS had lower plant area. However, within treatments, differences between genotypes were only found when comparing among growth habit. Traditional and heirloom genotypes reduced their leaf mass per area (LMA) as compared to modern genotypes in CS. A similar pattern was observed in δ13C, with lower values for the modern genotypes. These results can be partially explained by the consistently lower stomatal conductance (gs) of the traditional genotypes as compared to the modern ones. Thus, there was a negative relationship between leaf δ13C and gs, that was translated into a positive correlation between the former and the intrinsic water-use efficiency (WUEi). A reduction of total yield and fruit quality parameters in CS was observed also when comparing within genetic groups and fruit type. In conclusion, both traditional and heirloom genotypes were less affected by the CS treatment, being a suitable germplasm source to improve tomato crop.