Salinity impact on flowering and reproduction of Solanum lycopersicum and its wild halophyte relative Solanum chilense

Salinization of cultivated lands is of growing concern and represents high economical losses for farmers and countries, especially for glycophyte (salt-sensitive) species. Tomato (Solanum lycopersicum) is the second most highly produced vegetable worldwide, and is cultivated in several regions affected by salinity; however, this species is recognized as a glycophyte species. The use of salt-tolerant wild relative species such as Solanum chilense could be an efficient strategy to improve salt-resistance of tomato. This species can cope with harsh environments but has received minor attention until now. This thesis aims to compare the changes caused by salinity in S. lycopersicum and S. chilense during a long-term NaCl stress, with a special focus on the development of inflorescences and flowers. Plants were grown under greenhouse conditions and were exposed to 0, 60 and 120 mM NaCl from the seedling stage to fruit production, under hydroponic conditions (Hoagland nutrient solution in a mixture of perlite/vermiculite (50:50 v/v)). We showed that S. chilense was more salt-resistant than S. lycopersicum and that long-term salt stress had more deleterious effects than short-term salt stress in both species. Both species differed regarding salt-resistance strategies. Solanum chilense accumulated globally more Na+ in aerial parts than S. lycopersicum and the opposite occurred in roots, highlighting an ‘includer’ strategy of S. chilense and an ‘excluder’ strategy of S. lycopersicum. Ions contributed to osmotic adjustment in both species, mainly Cl- in S. lycopersicum and Na+ and K+ in S. chilense. A modification of leaf anatomy contributed to salt resistance in both species. Regarding the reproductive stage, salinity decreased the number of inflorescences in both species but the number of flowers per inflorescence was reduced only in S. lycopersicum. On the same way, fruit size and weight were reduced by salt only in S. lycopersicum. Both species limited the accumulation of Na+ and Cl- in the inflorescences and Na+ distribution inside the flower differed between species. Sodium was shown to accumulate primarily in the anthers of S. chilense and in the flower peduncle of S. lycopersicum. Salinity led to a decrease in the length of S. lycopersicum sepals, which could disrupt the source-sink relationship in flowers. Overall, our results indicated that S. chilense was more salt resistant than S. lycopersicum during reproductive phase and that differences in reproductive response could be related to dissimilarities in element distribution and transport in flowers, as well as disruptions in sugar partitioning during salt stress. In parallel, we hybridized S. lycopersicum and S. chilense and obtained fertile hybrids despite inter-specific reproductive barriers. They have an intermediate phenotype between both parents. Hybrids were cultivated under salt stress conditions, and showed globally an intermediate salt-resistance behavior although they displayed heterosis behavior for some parameters, as observed for water use efficiency. Altogether, this thesis highlighted that the two tomato species differ in their response to salinity at the physiological level and that their hybrids develop an intermediate strategy depending on the parameters.