Integrated approaches to increase quality and stress resilience in tomato

Tomato (Solanum lycopersicum) cultivation faces growing challenges due to climate-driven increases in temperature, drought, soil salinity, and heavy metal contamination, all of which negatively affect productivity both at qualitative and quantitative levels. The present thesis project addresses these challenges and has two main objectives: 1. to evaluate the response of four tomato inbred lines to either nickel toxicity or water stress. This part of the research was made in collaboration with the Italian company ISI Sementi S.p.A. The four lines were provided by ISI Sementi and are currently used in breeding programs to produce hybrids for commercial purposes. To evaluate the effects of nickel, experiments were conducted using hydroponic and soil systems. Morphological analyses were combined with the quantification of nickel and essential mineral nutrients in both shoots, roots, and fruits. Water stress responses were assessed at germination and during the adult growth stage through phenotypic, physiological, and molecular analyses. The multi-level approach allowed us to identify the two lines able to maintain fruit quality parameters under nickel stress and to acclimatise to repeated water stress, which can be used for the creation of new commercial hybrids. Future research will assess whether these hybrids have acquired characteristics that allow them to be resilient to the combined stresses of nickel and water. This study offers a methodological approach for researchers and breeders to develop new varieties with enhanced resilience to multiple stressors. 2. to dissect the roles of AUCSIA genes (i.e. SlAUCSIA-1 and SlAUCSIA-2) in cv. MicroTom by genome editing using the CRISPR-Cas9 tool. From the literature, it is known that the AUCSIA gene family is implicated in auxin-related fruit set and root development (Molesini et al., 2009). Homozygous mutants for the SlAUCSIA-2 gene were already available in the laboratory, as they were obtained from previous research. In this thesis, transgenic plants harboring mutations in the SlAUCSIA-1 gene were obtained. In-depth phenotypic analyses conducted on slaucsia-1 and slaucsia-2 mutants revealed that both genes are involved in root development but play distinct roles. Specifically, slaucsia-2 mutants exhibited reduced primary root length and lower lateral root density, whereas slaucsia-1 mutants displayed increased lateral root length. Concerning the reproductive development, slaucsia-2 mutants exhibited an increased fruit set capacity after flower emasculation (i.e., evaluation of the parthenocarpic trait), whereas this trait needs further investigation in slaucsia-1 mutants due to problems that emerged during cultivation under greenhouse conditions. The reduced lateral root density observed in slaucsia-2 mutants prompted us to investigate potential biotechnological advantages, particularly in relation to salinity tolerance. The choice of testing the response of slaucsia-2 mutants to NaCl stress was based on the fact that it has been proposed that parsimonious root phenotypes are advantageous for high-input agroecosystems (Lynch, 2018), as observed in a salt-tolerant rice genotype showing reduced lateral root density compared to a sensitive genotype (Ijaz et al., 2019). In the presence of 100 mM NaCl, slaucsia-2 mutants exhibited reduced Na accumulation in shoots and at 200 mM NaCl the halotropic response was less pronounced compared to the WT plants, suggesting an increased capacity to cope with salinity stress.