• Drought
• Landraces
• Salinity
• Tolerance
• Tomato

During the last century, the strong anthropic pressure and the global climate changes have exacerbated the depletion in water resources availability in term of quantity and quality. The expected scenario will be more catastrophic, especially in arid areas including the Mediterranean Basin. More frequent and severe extreme weather events will negatively affect food production, especially to keep up with the projected population growth. The development of crop plants well adapted to harsh climatic conditions such as drought and salinity will become essential to increase or even maintain the actual levels of food productivity. The identification and characterization of crop germplasm with high water use efficiency remains a hopeful sustainable strategy to provide food and valorise marginal areas. A deeper understanding of plant adaptive physiological and molecular mechanisms will be invaluable to select such germplasm. Biodiversity represents a target for scientific investigations and consequently a source for new breeding strategies. Landraces are members of that part of plant biodiversity which is often well-adapted to wild environments and extreme conditions. In the Mediterranean area, tomato (Solanum lycopersicum L.) is often exposed simultaneously to drought and salinity and many tomato landraces showed high adaptation capacity to these stress conditions.
The objective of this thesis was to investigate the salt and drought tolerance capacity of "Ciettacale", a Southern Italy tomato landrace, as observed by local farmers in comparison with commercial tomato cultivars ("San Marzano", "Moneymaker", "UC-82B") at different phenological stages; with this purpose, physiological, biochemical and metabolic parameters were used.
The biochemical profile and germination rate of Ciettaicale and San Marzano were clearly altered by a moderate concentration of sodium chloride (25 mM NaCl) during 5 days-experimental time-course. Salt induced a promotion of endosperm weakening-related enzymes endo-beta-mannanase and beta-mannosidase activities in Ciettaicale, as well as starch mobilization, contributing both to the enhancement of total soluble sugars, and also to the scavenge oxidative capacity, as indicated by increased total antioxidant and catalase activities. Conversely, in San Marzano, we found some salinity-induced physiological changes only at the end of our experimental observations, suggesting that seeds were not dormant, but impaired by the stress to to properly achieve or complete the germination process.
Leaf gas exchange and chlorophyll a fluorescence measurements supported by growth and biochemical analyses were evaluated to identify salt tolerance differences between Ciettaicale and San Marzano during the vegetative stage under short-time high salinity stress (0, 300, 450 and 600 mM NaCl). After a week of salt treatments, salinity effects culminated in photoinhibition and/or photodamage events at 600 mM NaCl in San Marzano plants resulting in a source-sink imbalance. Among the salt gradient, Ciettaicale plants showed an efficient physiological and metabolic plasticity provided by improved photosynthesis efficiency and osmotic adjustment resulting in a higher energy availability to be used in root exploration. Thus, the Ciettaicale NaCl tolerance strategy allowed this landrace to survive or at least to slow down the appearance of actual damages at high NaCl concentrations.
We also combined chlorophyll a fluorescence measurements and metabolic determinations to investigate the performance of Ciettaicale and Moneymaker plants subjected to 20 days-drought stress. Physiological and metabolic changes, in terms of abscisic acid (ABA), indol-3-acetic acid (IAA), proline, soluble sugars and phenols contents, occurred in both Ciettaicale and Moneymaker under water deficit. Our results highlighted the ability of Ciettaicale to manage plant water status under drought in order to preserve both leaf and root activities. This strategy was achieved thanks to the preservation of the source-sink relations: a more efficient PSII photochemistry at leaf level associated with a major investment in root growth and activity in order to improve water uptake. On the contrary, drought-stressed Moneymaker plants reduced electron transport rate and enhanced starch reserve mobilization in both leaves and roots, possibly suggesting a major role of the osmotic adjustment to counteract tissue dehydration, but meantime a feedback potential disruption of source-sink relations. This hypothesis was also supported by the more pronounced redox state disequilibrium, as suggested by the higher hydrogen peroxide and malondialdehyde contents, that affected both PSII photochemistry and root activity and markedly trigged in turn the non-photochemical fluorescence quenching (NPQ) and antioxidant responses by Moneymaker plants compared to Ciettaicale.
In an autumn-winter greenhouse hydroponic experiment we evaluated yield and fruit quality of Ciettaicale under salt stress, in comparison with other two Southern Italy tomato landraces (Linosa and Corleone) and one commercial cultivar (UC-82B) Salt treatments (60 mM and 120 mM NaCl) promoted the anticipation of fruit ripening in landraces and UC-82B compared to non-salt conditions. At harvest, no losses in marketable yield were noticed in all genotypes. Instead, fresh and dry fruit yields, as well as cation concentrations, were more affected under stress in the commercial cultivar as compared to landraces. Different trends of lycopene content and soluble sugars amount were found in the fruits among all investigated accessions. Data obtained by UPLC-MS revealed differential accumulation of glycoalkaloids, phenolic acids, flavonoids and their derivatives in the landrace fruits under stress in all genotypes. Overall, despite the non-optimal environmental conditions represented by salt stress and off-season light irradiance/temperature, our results showed a differentiation between the Italian landraces and the commercial variety UC-82B under 60 mM NaCl: in this stress condition, landraces showed a tolerable compromise between yield and quality attributes. Conversely, off-season high salinity stress (120 mM NaCl) significantly reduced the antioxidant activity both in UC-82B and in the landraces.
Our data suggested that Ciettaicale could carry interesting traits at vegetative stage such as improved root/shoot ratio, water use efficiency, osmotic regulation and maintenance of shoot-to-root relationships under high salinity and water deficit, as well as good performance in term of germination rate and fruit yield and quality under salt stress. We point to the feasible use of the tomato landrace Ciettaicale as a target to select interesting genetic traits to improve stress response and fruit functional values. Thus, deep investigations are required in order to enhance the possibility of introducing this landrace in tomato genetic improvement programs.