FYSIOLOGISCHE EN GENETISCHE FACTOREN DIE HET BLOEIGEDRAG VAN APPEL (MALUS DOMESTICA BORKH.) REGULEREN

Apple (Malus x domestica Borkh.) is one of the main fruit tree crops cultivated in the world, and the most widely grown species of the genus Malus. One of the major challenges for the apple breeding industry is to overcome juvenility, i.e. the developmental phase at which the tree is dedicated to vegetative growth and hence is not competent to flower. The juvenile period in apple can last up to 8 years, hence strongly delaying phenotype-based selection of desired cultivars, and additionally impairing rapid accumulation of genetic gain via repetitive cross-breeding. As a consequence, the introduction of new apple cultivars into the market is a long and costly process that may take more than 20 years. In Arabidopsis and other plant model organisms microRNA156 is one of the major regulators. In higher plants, miR156 targets transcripts of the Squamosa Promoter Binding Protein-like (SPLs) genes, which promote the juvenile-to-adult transition. Interestingly, studies in Citrus have shown that the miR156-SPL cascade not only regulates acquisition of flowering competence, but also is involved in the regulation of biennial bearing. The main goal of this project is to develop a genetics toolbox as well as agronomic methods to shorten the juvenility phase in apple to hence significantly shorten the apple breeding cycle. In parallel, proposed research project also aims to characterize the underlying genetic factors that regulate biannual bearing.