Locally-adapted Italian cultivars of tomato (Solanum lycopersicum L.) under drought stress: morpho-physiological, biochemical and nutraceutical aspects underlying stress tolerance

Background: Water deficit is one of the 21st century's major challenges, agriculture being both the cause and the victim since 70% of global available water is used for its practices. Irrigation is fundamental but, as climate change becomes more persistent, there is a need to conserve water and use it more efficiently. Exposure of plants to drought stress can cause morphological, anatomical, physiological, and biochemical changes in many tissues and organs. Drought can affect the growth and development of plant organs causing drastic reduction in productivity and commercial performance. It is therefore crucial to identify cultivars that can tolerate drought. When dealing with economically relevant crops like tomatoes, this purpose is even more incisive and local agrobiodiversity is a large genetic reservoir of promising cultivars. Aims and Methods: Nine local Italian and four commercial tomato cultivars were considered. All experienced approximately 20 days of drought during the vegetative and reproductive phases. Plants were studied for three aspects. Morpho-physiology: several physio-morphological parameters were monitored, such as stomatal conductance, photosynthesis, water use efficiency, growth, and soil water content. The different responses and behaviors allowed the cultivars to be divided into three groups: tolerant, susceptible, and intermediate. The classification was also confirmed by the principal component analysis. Biochemistry: the expression of proteins related to drought stress tolerance in four local tomato cultivars was evaluated. Cultivars were selected after the results of previous analyses and corresponded to different tolerance levels. Only the vegetative stage was considered in this section. The approach consisted of extraction, separation, and immunological analysis of proteins such as dehydrins, osmotin, HSP70s, sucrose synthase, and cyclophilin. We also analyzed the pattern of phosphorylated proteins and the isoforms of RuBisCO. Nutraceutics: Genetic factors, ripeness and the impact of environmental conditions lead to differences in the bio-metabolic and nutraceutical composition of tomato fruit. We tested the hypothesis that local tomato cultivars subjected to drought stress showed an increased capacity for biosynthesis of compounds with antioxidant activity. The antioxidant power and the total content of polyphenols and flavonoids in both pulp and peel were evaluated by colorimetric assays. In addition, flavonoids (such as rutin, naringenin, and caffeic acid), vitamin C, and lycopene were identified and quantified using HPLC methods. Results and Conclusions: At last, the data obtained at the morphological, physiological, biochemical, and metabolic levels indicate that specific locally adapted tomato cultivars respond much more efficiently to drought stress, even more than widespread commercial cultivars. In addition, this study lays the foundations for an application aspect, namely the use of moderate and controlled drought stress conditions to increase the nutritional quality of tomato fruits. Given that many bioactive compounds are found in the peel of tomatoes, this supports the reuse of waste components and therefore their sustainable recovery.