|Title||Two large-effect QTLs, Ma and Ma3, determine genetic potential for acidity in apple fruit : breeding insights from a multi-family study|
|Author(s)||Verma, S.; Evans, K.; Guan, Y.; Luby, J.J.; Rosyara, U.R.; Howard, N.P.; Bassil, N.; Bink, M.C.A.M.; Weg, W.E. van de; Peace, C.P.|
|Source||Tree Genetics and Genomes 15 (2019)2. - ISSN 1614-2942|
|Publication type||Refereed Article in a scientific journal|
|Keyword(s)||FlexQTL™ - Malic acid - Malus × domestica - Pedigree-Based Analysis - RosBREED|
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.