# Breeding Tomato Hybrids for Flavour: Comparison of GWAS Results Obtained on Lines and F1 Hybrids
## 1 Introduction
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Full Name** & **VOC ID** & **Met. Path** & **Aroma. Impact** & **Aroma. Descriptors** \\ \hline Benzaldehyde & BENZA & B & + & Almond, burnt sugar, peaches, fruity \\ Eugenol & EUGEN & B & – & Sweet, spicy, clove, woody, pharmaceutical \\ Guaiacol & GUAIA & B & \(\star\) & Phenolic, smoke, spice, vanilla, woody \\ p-cymene & PCYM & B & \(\star\) & Solvent, gasoline, citrus \\ Salicylaldehyde & SALI & B & – & NA \\
1-nitro-3-methylbutane & 1N3 MBUT & BCAA & + & NA \\
2-isobutylthiazol & 2 ISOBUT & BCAA & + & Tomato, leafy, green, pungent, medicinal \\
3-methylbutanal & 3 MBUT & BCAA & + & Ethereal, aldehyde, chocolate, peach, fatty, malt \\ \(\beta\)-damascenone & B ADAM & C & \(\star\) & Apple, rose, honey, tobacco, sweet \\ \(\beta\)-ionone & BIONO & C & \(\star\) & Floral, sweet \\ Geranylacetone & GRACE & C & \(\star\) & Sweet, floral, estery, citrus \\ Gerani & GRIAL & C & \(\star\) & Sharp, lemon, sweet \\ Neral & NERAL & C & \(\star\) & Lemon \\
6-methyl-5-hepten-2-one & 6 MHON & C & + & Fruity, floral, sweet \\ (E)-2-heptenal & E2 HEP & L & + & Dried fruits \\ (E)-2-pentenal & E2 PEN & L & + & NA \\ (E,E)-2,4-decadienal & EE24D & L & \(\star\) & Earthy, musty \\ (E,E)-2,4-hexadienal & EE24H & L & \(\star\) & Green \\ Heptanal & HEPTAL & L & \(\star\) & Fat, citrus, rancid \\ Hexanal & HEXAL & L & \(\star\) & Grass, tallow, fat \\
1-penten-3-one & 1P3 ON & L & + & Fruity, floral, green, fresh, sweet \\
2-ethylfuran & 2 EFUR & L & \(\star\) & Rum, coffee, chocolate \\
3-methylfuran & 3 MFUR & L & \(\star\) & NA \\
3-pentanone & 3 PONE & L & + & NA \\ (Z)-3-hexenal & Z3 HEX & L & \(\star\) & Leafy, green, grass, tomato \\ Phenylacetaldehyde & PHEAC & Phe & + & Hawthorne, honey, sweet \\
2-phenylethanol & PHENE & Phe & + & Honey, spice, rose, lilac \\
1-nitro-2-phenylethane & 1N2 PHERE & Phe & + & Flower, spice \\ Linalool & LIN & T & \(\star\) & Citrus, fruity, sweet taste \\ \hline \hline \end{tabular} VOCs impacting flavour perception are marked with a (\(\uparrow\)) in column “Aroma.impact” when their odour threshold or abundance is at stake (reviewed in [14; 15; 16]). VOCs with positive (resp. negative) significant correlation to consumer liking are marked with a (\(\star\)) (resp. (\(-\))) [8] (adapted from [8]). VOCs abbreviations are specified in “VOC ID” B: benzenoid, BCAA: branched-chain amino acid, C: carotenoid, Phe: phenylalanine, T: terpenoid, NA: not available.  
\end{table} 
Table 1: Important VOCs for consumer liking among the 46 VOCs, SSC and fruit weight (adapted from [8]). tigated by [17] in a Recombinant Inbred Lines (RILs) population. They highlighted several chromosome regions aimed at providing breeders with efficient tools for Marker Assisted Selection (MAS). Introgression Lines (ILs) derived from crosses between domesticated tomato (_Solanum Iycopersicum_) and the wild species _Solanum pennellii_ concomitantly enabled the cloning of major genes regulating key VOC synthesis [18; 19]. Other tomato wild relatives such as _Solanum Pimpinellifolium_ or _Solanum Habrochaites_ have also been studied through biparental segregating populations and provided new QTLs for flavour-related traits as reviewed in [20]. Precise QTL mapping allowed by genome-wide association studies (GWAS) later brought better resolution around QTLs, with the dissection of previously identified large genomic regions into many single QTLs, which provided easier identification of candidate genes ('CGs') [21; 22; 23]. Although tremendous improvement has been achieved for QTL identification on homozygous plant material [20], breeders still need insight into the flavour improvement they can expect from these QTLs in their F1 hybrids, as no study has yet been undertaken on the evolution of flavour-related traits within heterozygous plant material. In the European Union, 89% of registered tomato varieties were hybrids in 2018 [24].