Multiple genetic analyses disclose the QTL dynamic for fruit texture and storability in Norwegian apples (Malus domestica Borkh.)

Abstract

In Norway, apples (Malus domestica Borkh.) are produced at latitude around 60° north. Notably the season is short and cool and Norwegian cultivars have developed under selection pressure from these distinct climatic conditions, resulting in apple germplasm with unique genetic structure and pedigree. Strong selection for earliness has resulted in several cultivars that mature and soften quickly, making it challenging to meet consumer expectations for apple quality. The commercial success of apple is largely related to its texture and long-term storability, enabling a year-round availability of fresh fruit. Texture in apple has been well characterized and major causative genes have been found. Nonetheless, comprehensive knowledge of the genetic control of texture retention is lacking. To improve postharvest performance, including storability, in the breeding program currently ongoing at Njøs Fruit and Berry Centre (NJØS), a diversity collection of 197 apple cultivars was employed to initiate a genome-wide association analysis (GWAS) to identify relevant genomic regions associated with these aspects. Quantitative trait loci (QTL) associated with different dissected multi-trait texture components assessed by a texture analyzer equipped with an acoustic device were identified. To target QTLs relevant to improving postharvest storage, a softening and storage index was also implemented into the QTL analysis, further mapped on chromosome 10. The GWAS-QTL pattern was additionally validated on a different genetic background, implementing a multi-parental-cross-design scheme. Findings include previously unreported genomic regions related to texture attributes, and especially haploblock HB-10–03 represents an important novel molecular tool valuable for breeding Norwegian apple cultivars with superior fruit storability.