GENES AND GENOMIC REGIONS RELATED TO THE PRODUCTION OF VOLATILE COMPOUNDS IN THE TOMATO FRUIT

Fruits both produce and emit volatile chemical compounds. These are short-chained low polarity molecules involved in many processes, and they are responsible of our perception of fruit aroma and of most of their flavour. This thesis is focused on the study of volatile compounds in the tomato fruit, which is one of the most important horticultural crop worldwide and is a model system for the study of fruit development and ripening. Some of the analytical methods more frequently used for the analysis of tomato fruit volatiles were systematically compared. Results revealed that the observed volatile profile is highly dependent on the precise analytical method used, both for sample processing and for the technique used for volatile acquisition. It was concluded that the method of election for the comparison of large sets of samples from a multi-omics approach consists on flash freezing the biological material with liquid nitrogen at the selected ripening stage and the use of headspace solid phase microextraction coupled to gas chromatography and mass spectrometry for the subsequent analysis. This method was implemented and was used for the determination of volatile compounds in selected NILs harbouring QTLs for characters related to flavour and aroma introgressed in different genetic backgrounds. The results allowed the association of several of the organoleptic characters previously identified with modified levels of several volatiles. It was also observed that the genetic background has a major effect on the production of such metabolites. Correlation analysis between the levels of volatiles and primary metabolites led to the conclusion that the production of volatile compounds is generally not determined by the levels of their precursors. Its regulation is most likely to be due to downstream processes such as the availability of either precursors or intermediate metabolites, the variability in specific processes leading to the conversion of precursors into volatiles, or to other still unknown regulatory mechanisms. Volatile compounds were also studied in a RIL population derived from a cross between Solanum pimpinellifolium accession TO-937, the closest species to cultivated tomato, which produces red fruits, and S. lycopersicum cv. ‘Moneymaker’, a tomato variety for the fresh market. This allowed the identification of 102 QTLs for 39 different volatile compounds, 76 of which had not been previously described. All these QTLs were mapped along the 12 tomato chromosomes by means of the SOLCAP SNPs molecular market map. Most of the QTLs identified were subsequently evaluated on introgression lines (ILs) generated from the same original genotypes. It was observed that almost half of the QTLs previously identified retained their effect after introgression in the ‘Moneymaker’ genetic background. Additionally, 16 new QTLs were identified in this IL population. Based on the existing knowledge about the effect of volatile compounds on our perception of flavour and aroma and also on their ability to maintain their effect after introgression in the cultivated tomato, some of the QTLs identified are good candidates to be used in tomato flavour breeding programs. Eventually, the comparison of the localization in the genome of the QTLs identified in the different populations studied with those already described in the literature revealed a very low degree of co-localization between the different QTLs. This implies that there exists a wide range of variability in the wild species related to tomato available for breeding tomato flavour and aroma.