Traditional varieties of tomato from the Mediterranean region represent a pool of biodiversity that can be mined for novel traits useful for the genetic improvement of commercial varieties. The TOMRES project aims at improving water and nutrient use efficiency in tomato through novel combinations of genotypes and management practices. Within this framework, we have tested a set of 27 accessions from Southern Italy and Spain as well as backcross inbred lines (BILs) from Israel to identify genotypes that are particularly efficient in their use of water, nitrogen, or both critical resources. Genotypes were first tested in vitro for early responses to stress. Parameters related to root architecture, such as primary root length, number and length of lateral roots were evaluated under Control conditions, Low Nutrient conditions (1/10 of control N and P dose), Osmotic stress (200 mM Mannitol), and a combined stress treatment (Low nutrients and mannitol). A subsequent evaluation involved several rounds of a large scale pot-experiment using 15 L pots filled with sand in a randomized block setup. Each genotype was grown for six weeks under four separate treatments: Control (10.2 mM NO3 -), Low Nitrate (2.88 mM NO3 -), Drought (50% water) and Combined Stress. Chlorophyll content, stomatal opening and relative water content were monitored throughout the growth cycle. At harvest above and below ground growth parameters were measured. Biometric measurements were subjected to analysis of variance (ANOVA) and Duncan post-hoc test. This showed that above ground parameters were largely in agreement and demonstrated a significantly reduced growth in stress treated compared to control plants, with two exceptions. Growth of genotype TOMRES250 was not repressed under drought or combined stress, while for genotype TOMRES271 drought stress alone did not cause reduced biomass accumulation. Interestingly, TOMRES250 had a less developed root system, stable across the different treatments, while TOMRES271 root system did not modify in response to drought stress. We thus calculated the root dry weight/shoot dry weight ratio and found that TOMRES250 and 271 did not modify biomass allocation based on the stress treatment, in contrast to the remaining tested genotypes, which had a significant alteration of this parameter due to stress. Thus, root systems that maybe preadapted to stressful environments may contribute to tolerance displayed in terms of growth of above ground tissues. Molecular analyses also showed a different transcript abundance of nitrogen uptake and transport-encoding genes in TOMRES250, indicating that a more efficient nutrient uptake may characterize this genotype. Ion content analysis is in progress to confirm this hypothesis. In conclusion, we have set up a screening system and identified two candidate genotypes that show resilience to environmental stresses. Molecular and biochemical analyses are in progress to dissect the molecular basis of this behavior. This work was supported by the European Union’s Horizon 2020 research and innovation programme under the Grant Agreement No. 727929.
