Genetic determinism of budbreak timing in apple, a pedigree based analysis approach

Since the late 80’s, significant increases of mean temperatures has been recorded worldwide. This change leads to earlier flowering dates in apple, possibly making frost damage and phenological disorders related to fruit setting more frequent. This situation urges studies on genetic determinism of chilling and heat requirements in apple tree leading to timing of bud phenology.
The present study aimed at clarifying the genetic determinism of timing of budbreak for five full sib families related by their pedigrees. Two of these families are located in Montpellier, South-East of France, and three in Angers, North-West of France. Up to five development stages, green point, vegetative budbreak, floral budbreak, flowering and end of flowering, were observed for the five families, over two years. The climatic years and locations were characterized by the duration of chilling and heat requirement completion for a reference cultivar ‘Golden Delicious’.
On that basis, mixed models were used to estimate the genotype effects and the GxE interaction effects. The five populations were also genotyped with the Illumina 20k SNP array within the EU-FP7 project FruitBreedomics. These SNP data and the Best Linear Unbiased Prediction values on genotypes and GXE interaction for the different phenological stages are used for pedigree-based QTL mapping with the FlexQTLTM software. The outcomes of this study will provide new insights on the genetic determinism of timing of budbreak in apple, leading to new tools for apple breeders.