Global analysis for modelling pepper plant response to salt stress

Salt accumulation in soil is a major problem in agriculture, especially in arid and semi-arid regions, as Mediterranean areas. Salinity affects plant growth at molecular, biochemical and physiological scale and it severely limits crop production and fruit quality. Pepper (Capsicum annuum L.), a moderately sensitive vegetable crop to salinity, is largely cultivated in areas characterized by saline water and/or water deficiency. For these reasons, the selection of genotypes tolerant to salt stress and , with improved fruit quality, represents a crucial aim for breeding programmes. In order to characterize pepper response to different salt concentrations, we adopted an integrated approach with the purpose of combining molecular, biochemical and physiological features measured on salt-stressed plants, with particular emphasis on fruit quality. In our experimental plan, two sweet pepper genotypes ('Quadrato D'Asti' and 'Cazzone Giallo') were grown in a closed soilless system and exposed to moderate and high salt levels (0-30-90-120 mM NaCl in nutrient solution) during the whole crop cycle. Data were collected at different stages of plant growth (vegetative and reproductive) from different tissue types including leaves and fruits. Plant phenotypic (biomass and yield) and physiological characterization (gas exchanges, total water potential and osmotic potential) were performed together with gene expression analysis and metabolic profiling (targeted and untargeted metabolomics). The agronomic traits were strongly affected by salinity, which determined a decrease of leaf photosynthetic rate and of related parameters and a reduction in the fruit fresh weight and number of fruits per plant (marketable fruits). Interestingly, increasing salinity levels did not cause any detrimental effect on fruit quality (pH, citric acid, °Brix). Furthermore, salt stress induced the accumulation of proline and ABA in leaves and of different carotenoids during fruit ripening, as well as a change in volatile compounds profiles and levels. Results on molecular analysis indicated that plant developmental stage and long term salt treatments affect the expression of genes known to be involved in ion transport, osmolyte biosynthesis and other stress-related functions. By integrating physiological, biochemical and molecular datasets, we aim to construct correlation networks in order to develop a model describing pepper plant response to salt stress and its effects on fruit quality.This work was funded by Ministry of Education, University and Research, PON Project GenHORT (PON02_00395_3215002).