S11 - Session O2 - Elucidating the molecular mechanism of dormancy control and bud break in apple to prepare for climate change

Authors: Janne Lempe *, Xiaoying Chen, Vincent Bus, Henryk Flachowsky, Andreas Peil, Satish Kumar

Winter dormancy is a crucial phase in all deciduous trees that is required for survival of buds under harsh winter conditions. Onset and release of dormancy are tightly regulated by environmental cues, with ambient temperature playing a major role. Increasing temperatures through global warming negatively affect the timing of dormancy progression and bud break. As consequence, flowering occurs either irregularly or too early and inevitably leads to yield losses. To enable the breeding of new apple cultivars that are more resilient to climate change, loci that control dormancy progression and bud break need to be identified to develop genetic markers for targeted selection. An F1 population derived from the cross between the M. domestica cultivar 'Rote Sternrenette' and M. orientalis MAL0940 was used for a quantitative trait loci (QTL) mapping approach. In parallel, genome wide association (GWAS) analyses for bud break and dormancy transitions were performed at the New Zealand Institute for Plant and Food Research Limited, using the local strain collection comprising 398 old cultivars, 27 rootstocks and 17 wild species accessions. From the first year's phenotypic analysis, we identified a major QTL on top of chromosome 9. The known flowering time genes MdFLC-like and MdICE1 are located within this QTL region, and represent good candidate genes for dormancy control. Both genes were shown to be expressed throughout winter dormancy. Expression of MdICE1 peaks during the first dormancy phase called endodormancy, and expression of MdFLC-like peaks during the transition to the second dormancy phase called ecodormancy. As next steps, expression patterns of these genes will be tested in both parents and will be associated with genetic variation in proximity of these candidate genes that co-segregates with the flowering time behaviour in this population. This information will allow the development of useful molecular markers for apple breeding.