Abstract
Improvement of nutritional and organoleptic quality of fruits is a key goal in current strawberry breeding programs. The ratio of sugars to acids is a determinant factor contributing to fruit liking, although different sugars and acids contribute in varying degrees to this complex trait. A segregating F1 population of 95 individuals, previously characterized for several fruit quality characters, was used to map during 2 years quantitative trait loci (QTL) for 50 primary metabolites, l-ascorbic acid (L-AA) and other related traits such as soluble solid content (SSC), titratable acidity (TA), and pH. A total of 133 mQTL were detected above the established thresholds for 44 traits. Only 12.9% of QTL were detected in the 2 years, suggesting a large environmental influence on primary metabolite content. An objective of this study was the identification of key metabolites that were associated to the overall variation in SSC and acidity. As it was observed in previous studies, a number of QTL controlling several metabolites and traits were co-located in homoeology group V (HG V). mQTL controlling a large variance in raffinose, sucrose, succinic acid, and L-AA were detected in approximate the same chromosomal regions of different homoeologous linkage groups belonging to HG V. Candidate genes for selected mQTL are proposed based on their co-localization, on the predicted function, and their differential gene expression among contrasting F1 progeny lines. RNA-seq analysis from progeny lines contrasting in L-AA content detected 826 differentially expressed genes and identified Mannose-6-phosphate isomerase, FaM6PI1, as a candidate gene contributing to natural variation in ascorbic acid in strawberry fruit.
Highlights
Strawberry is one of the most important soft fruit crops in the world and its quality is largely tied to the ripening process
As an initial approach to assess the variation in primary metabolism in fruits, we investigated which metabolites were present in ripe fruit extracts from parents and F1 progeny lines from the cross of selection lines ‘232’ and ‘1392’
This study identified numerous mQTL for primary metabolites accumulating in ripe strawberry fruit
Summary
Strawberry is one of the most important soft fruit crops in the world and its quality is largely tied to the ripening process. The receptacle experiences auxin-dependent phases of division, expansion and ripening, and sugars, organic acids, Vallarino et al Horticulture Research (2019)6:4 increasing soluble solids content (SSC) as an approximation of total sugar content and the SSC:titratable acidity (TA) ratio[3]. Breeding has aimed to maintain, or increase, the content of nutraceutical compounds[4]. Breeding more nutritious and better tasting cultivars can be achieved by introgressing natural trait variation, which requires understanding the heritability of those traits. In this regard, QTL analysis provides information on the genetic control of traits useful for breeding new varieties through marker-assisted selection, and on the relationships among genes influencing the traits
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