Certain cherry tomato accessions have been shown to be most flavorful among tomato cultivars. In order to study organoleptic quality through all of its components, a QTL experiment was designed using the progeny of a cherry tomato line (Cervil, with high quality fruit) and a classical inbred line for fresh market (Levovil, producing large fruit with a common taste) (Causse et al. 2001, 2002; Saliba-Colombani et al. 2001). A population of 144 RILs was developedfrom crossingthese two lines. Progeny were characterized for physical and chemical traits such as color, weight, firmness, pH and titratable acidity, sugars and soluble solids content, concentration of
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S. pennellii | S. habrochaites S. pimpinellifollium
S. peruvianum | S. neorickii | S. Zyc. cerasiforme
Fig. 8. Summary of QTL for firmness in one of the following progeny: S. lycopersicum x S. pennellii introgression lines (Causse et al. 2004, unpublished data); S. lycopersicum x S. pennellii advanced backcross population (Frary et al. 2004); S. lycopersicum x S. habrochaites advanced backcross population (Bernacchiet al. 1998b); S. lycopersicum x S.pimpinellifolium advanced backcross population (Tanksley et al. 1996; Doganlar et al. 2002c); S. lycopersicum x S. peruvianum advanced backcross population (Fulton et al. 1997); S. lycopersicum x S. neorickii advanced backcross population (Fulton et al. 2000); S. lycopersicum cv cerasiforme x S. lycopersicum (Saliba-Colombani et al. 2001). The QTLs were positioned on the tomato reference map (Tanksley et al. 1992) based on the nearest marker
12 aroma volatiles, and for sensory traits based on a panel of 56 judges. Judges were trained to quantify their sensory perceptions of taste (sourness, sweetness), aroma (lemon, candy, citrus, pharmaceutical aroma) and texture (meltiness, firmness, mealiness, juiciness). A genetic map was obtained from the RIL population and was used to map QTLs for the measured traits. For each trait, one to five QTLs were detected. These QTLs explained 9 to 45% of the pheno-typic variation with some QTLs having major effects (e.g., those for six aroma volatiles) (Saliba-Colombani etal. 2001). Surprisingly, most QTLs were grouped within a few clusters (Causse et al. 2002). Alleles improving all fruit quality traits originated from the cherry tomato line (Causse et al. 2001, 2002). Despite the low heritability of sensory traits, QTLs could be detected for these traits and were often consistent with the location of QTL using mechanical measurements (Fig. 9).
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