Abstract
Acidity is a critical component of the apple fruit consumption experience. In previous biparental family studies, two large-effect acidity QTLs were reported using freshly harvested fruit. Objectives of this study were to determine the number and location of QTLs for acidity variation in a large apple breeding program and ascertain the quantitative effects and breeding relevance of QTL allelic combinations at harvest and after commercially relevant periods of cold storage. Pedigree-connected germplasm of 16 full-sib families representing nine important breeding parents, genotyped for the 8K SNP array, was assessed for titratable acidity at harvest and after 10- and 20-week storage treatments, for three successive seasons. Using pedigree-based QTL mapping software, FlexQTL™, evidence was found for only two QTLs, on linkage groups 16 (the reported Ma locus) and LG 8 (here called Ma3) that jointly explained 66 ± 5% of the phenotypic variation. An additive allele dosage model for the two QTLs effectively explained most acidity variation, with an average of + 1.8 mg/L at harvest per high-acidity allele. The more high-acidity alleles, the faster the depletion with storage, with all combinations appearing to eventually converge to a common baseline. All parent cultivars and selections had one or two of the four possible high-acidity alleles. Each QTL had a rare second high-acidity allele with stronger or reduced effect. Diagnostic SNP markers were identified for QTL alleles derived from distinct sources. Combined QTL effects highlighted utility of the DNA-based information in new cultivar development for targeting desired fruit acidity levels before or after storage.
Highlights
Acidity is a critical component of the apple fruit consumption experience
Titratable acidity (TA, in mg/L malic acid equivalents) using an Auto-Titrator (Metrohm 815 Robotic USB Sample Processor XL, Metrohm USA, Inc., Riverview, FL, USA) was determined for fruit of the germplasm set over three harvest years with three storage treatments within each year: at harvest with no storage (H); after 10 weeks of cold storage followed by 1 week at room temperature (10wk); and after 20 weeks of cold storage followed by 1 week at room temperature (20wk), as described by Evans et al (2012)
Two large-effect QTLs influencing apple fruit acidity levels before and after commercially relevant fruit storage treatment were detected in US breeding germplasm
Summary
Acidity is a critical component of the apple fruit consumption experience. Apple fruit are popular worldwide, consumed as either fresh or processed products and contributing to human health and well-being (Iwanami et al 2012). Fruit acidity affects overall apple flavor and the perception of other flavor traits such as sweetness and aroma, influencing consumer satisfaction (Harker et al 2003; Iwanami et al 2012). Malic acid content declines (Haynes 1925; Kouassi et al 2009) and can reach low levels associated with lower satisfaction for some segments of consumers (Harker et al 2008). There is genetic variation for acidity levels before and after storage among common cultivars (Rouchaud et al 1985; Iwanami et al 2008) and among germplasm in breeding programs (Ma et al 2015b; Cliff et al 2016). An understanding of the components of that genetic variation for fruit acidity would aid development of new apple cultivars that produce fruit with target levels of acidity
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
