|Guan, Yingzhu - Washington State University|
|Peace, Cameron - Washington State University|
|Verma, Sujeet - Washington State University|
|Evans, Kate - Washington State University|
Submitted to: Molecular Breeding
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/12/2014
Publication Date: 5/30/2015
Citation: Guan, Y., Peace, C., Rudell Jr, D.R., Verma, S., Evans, K. 2015. QTLs detected for individual sugars and soluble solids content in apple. Molecular Breeding. doi: 10.1007/s11032-015-0334-1.
Interpretive Summary: Selecting for sweetness traits in apple by MAS would improve the efficiency and reduce the cost for 243 breeding programs. In this study, we identified, for the first time, QTLs for sweetness-related traits (fructose, 244 glucose, sucrose, and sorbitol, except that SSC were reported before), which would be an important step toward 245 employing MAS to overcome the limitations of the phenotype-based conventional breeding. 246 QTLs for SSC in apple were reported in three studies; however, there is no published report of QTLs for 247 individual sugars in apple. Liebhard et al. (2003) reported QTLs for SSC in a ‘Fiesta’ × ‘Discovery’ population on 248 LGs 3, 6, 8, 9, and 14, but the precise locations were not presented. Kenis et al. (2008) reported QTLs for SSC on 249 LGs 2 and 10 in the ‘Telamon’ × ‘Braeburn’ population in 2004 and 2005. Potts et al. (2014) reported that there 250 were no QTLs detected for SSC in the population of ‘Co-op 17’ × ‘Co-op 16’ in 2008 and 2009. QTLs for SSC in 10 2004 in the study of Kenis et al. (2008) were located at the bottom of LG 2, which was similar 251 to the region where 252 QTLs for SSC were detected in our study (although only in one of the two years). Many factors could lead to our 253 different findings from the above studies, including environmental differences, genetic backgrounds, population 254 sizes, harvesting and sampling protocols, and the statistical model for QTL detection.
Technical Abstract: Sweetness is one of the most important fruit quality traits in breeding programs, determining the overall quality and flavor-perception of apples. Selecting for this trait using conventional breeding methods is challenging due to the complexity of its genetic control. In order to improve the efficiency of trait selection via DNA-based markers, extensive studies focused on the detection of quantitative trait loci (QTL) and development of DNA-based markers associated with QTL regions for traits of interest. Newly discovered QTLs detected in multiple apple breeding populations, are presented here for individual sugars (fructose, glucose, sucrose, and sorbitol) and soluble solids content (SSC) at harvest, after 10 weeks (10wk), and 20 weeks (20wk) of refrigerated storage followed by one week at room temperature in two successive years. A total of 1416 polymorphic SNPs were filtered from the RosBreed Apple SNP Infinium® array for QTL analysis using FlexQTL™ software. QTLs for individual sugars were identified on linkage groups (LG) 1, 2, 3, 4, 5, 9, 11, 12, 13, 15, and 16, and QTLs for SSC were found on LGs 2, 3, 12, 13, and 15. One QTL region on LG 1 was consistently identified for both fructose and sucrose from harvest through storage in both years, which accounted for 34-67%, and 13-41% of total phenotypic variation, respectively. These stable QTLs with high explained phenotypic variation on LG 1 for fructose content indicate a promising genomic region for DNA-based marker development to enable marker-assisted breeding for sweetness selection in apple breeding programs.