QTL mapping of bud break in apple aimed at facilitating breeding of cultivars resilient to climate change

We established a bilateral research project aiming to identify candidate genes that control the timing of endodormancy release and flowering time in order to modulate them in the breeding of new apple cultivars. We follow two complementary approaches: QTL mapping in an F1 mapping population in Germany and a genome-wide association study (GWAS) in New Zealand. These experiments will allow us to identify genomic regions and candidate genes that play roles in both processes. For the GWAS, an apple germplasm collection comprising 398 old cultivars, 27 rootstocks and 17 wild species accessions was genotyped and phenotyped. GWAS results will be presented elsewhere. For the QTL-mapping experiment, an F1 mapping population was developed from Malus domestica cultivar ‘Rote Sternrenette’ crossed with M. orientalis MAL940, which showed significant differences in timing of dormancy release and bud break. Dense genetic maps of both parents were generated after genotyping by RAD-seq (tGBS®). Here we present results from QTL mapping experiments for the trait vegetative bud break using phenotypic data obtained in 2020. A highly significant QTL for bud break was identified on LG9. This genomic region has been identified in previous studies investigating bud break and flowering time and comprises the candidate genes MdFLC-like and MdICE1. In future studies, this locus will be explored further for candidate genes based on allelic sequence variation in the parental accessions. Additionally, gene expression patterns of candidate genes across winter will affirm their possible roles in dormancy or bud break control. QTL mapping and GWAS are two complementary approaches that will increase our knowledge on the genes controlling dormancy, bud break and flowering time and will enable marker development for breeding new apple cultivars that are more resilient to climate change.