Abstract
BackgroundIn grapevine, as in other fruit crops, fruit size and seed content are key components of yield and quality; however, very few Quantitative Trait Loci (QTLs) for berry weight and seed content (number, weight, and dry matter percentage) have been discovered so far. To identify new stable QTLs for marker-assisted selection and candidate gene identification, we performed simultaneous QTL detection in four mapping populations (seeded or seedless) with various genetic backgrounds.ResultsFor berry weight, we identified five new QTLs, on linkage groups (LGs) 1, 8, 11, 17 and 18, in addition to the known major QTL on LG 18. The QTL with the largest effect explained up to 31% of total variance and was found in two genetically distant populations on LG 17, where it colocalized with a published putative domestication locus. For seed traits, besides the major QTLs on LG 18 previously reported, we found four new QTLs explaining up to 51% of total variance, on LGs 4, 5, 12 and 14. The previously published QTL for seed number on LG 2 was found related in fact to sex. We found colocalizations between seed and berry weight QTLs only for the major QTL on LG 18 in a seedless background, and on LGs 1 and 13 in a seeded background. Candidate genes belonging to the cell number regulator CNR or cytochrome P450 families were found under the berry weight QTLs on LGs 1, 8, and 17. The involvement of these gene families in fruit weight was first described in tomato using a QTL-cloning approach. Several other interesting candidate genes related to cell wall modifications, water import, auxin and ethylene signalling, transcription control, or organ identity were also found under berry weight QTLs.ConclusionWe discovered a total of nine new QTLs for berry weight or seed traits in grapevine, thereby increasing more than twofold the number of reliable QTLs for these traits available for marker assisted selection or candidate gene studies. The lack of colocalization between berry and seed QTLs suggests that these traits may be partly dissociated.
Highlights
In grapevine, as in other fruit crops, fruit size and seed content are key components of yield and quality; very few Quantitative Trait Loci (QTLs) for berry weight and seed content have been discovered so far
The extent of variation in berry weight was larger for the three table grape populations than for the SxG wine grape population, whereas it was more similar among populations for seed number, despite the large zero class in the seedless MTP3140 population
The second Quantitative trait locus (QTL) for berry weight found on Linkage group (LG) 18, near the VVIN83 marker, was stable over two years in our study, whereas it was found unstable by Cabezas et al [27]
Summary
As in other fruit crops, fruit size and seed content are key components of yield and quality; very few Quantitative Trait Loci (QTLs) for berry weight and seed content (number, weight, and dry matter percentage) have been discovered so far. Fruit size is a major determinant of both yield and quality for many crops with fleshy fruits. Berry size and number are major yield components for both table fruit and wine production. Small berry size is principally searched for to increase skin-to-flesh ratio, improving final concentrations of anthocyanins, tannins and aroma compounds in wine. These chemicals are primarily localized in the skin, but seeds are another important source of condensed tannins. The possible physiological correlation between berry size and seed quantity is a major issue in grape breeding
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