Genotype-by-environment and QTL-by-environment interactions in sweet cherry (Prunus avium L.) for flowering date

In sweet cherry (Prunus avium L.), flowering date is strongly dependent on the environment conditions and, therefore, is a trait of major interest for adaptation to climate change. Such trait can be influenced by genotype-by-environment interaction (GxE), that refers to differences in the response of genotypes to different environments. If not taken into account, GxE can reduce selection accuracy and overall genetic gain. However, little is known about GxE in fruit tree species. Flowering date is a highly heritable and polygenic trait for which many quantitative trait loci (QTLs) have been identified. As for the overall genetic performance, differential expression of QTLs in response to environment (QTL-by-environment interaction, QTLxE) can occur. The present study is based on the analysis of a multi-environment trial (MET) suitable for the study of GxE and QTLxE in sweet cherry. It consists of a sweet cherry F-1 full-sib family (n = 121) derived from the cross between cultivars 'Regina' and 'Lapins' and planted in two copies in five locations across four European countries (France, Italy, Slovenia and Spain) covering a large range of climatic conditions. The aim of this work was to study the effect of the environment on flowering date and estimate GxE, to carry QTL detection in different environments in order to study the QTL stability across environments and to estimate QTLxE. A strong effect of the environment on flowering date and its genetic control was highlighted. Two large-effect and environment-specific QTLs with significant QTLxE were identified on linkage groups (LGs) 1 and 4. This work gives new insights into the effect of the environment on a trait of main importance in one of the most economically important fruit crops in temperate regions. Moreover, molecular markers were developed for flowering date and a strategy consisting in using specific markers for warm or cold regions was proposed to optimize marker-assisted selection (MAS) in sweet cherry breeding programs.