A Multidisciplinary Approach to Study the Influence of Pollination and Plant Growth Regulators on Fruit Set and Early Fruit Development in Apple

Apple is susceptible to year-to-year differences in fruit production, mainly due to variation in levels of flower buds, pollination and fruit set. We present data of a multidisciplinary study to understand the underlying processes of fruit set and early fruit development and the factors which might influence this such as plant growth regulators and pollination conditions. Flowers and fruit were sampled in the field during the flowering period and the subsequent month. Cultivars ('Jonagold' and 'Golden Delicious') and pollination conditions (self-and cross-pollination) were compared, in some cases combined with a fruit set-promoting plant growth regulator (PGR). Pomological observations on fruit set and fruit growth were combined with transcriptional analysis of marker genes, morphological analysis of cell division and early fruit growth and the measurement of endogenous hormone contents (auxins and cytokinins). In addition, fruit and flowers of transgenic apple plants carrying cell cycle promoter:gus fusions were analyzed to get a better understanding of pollination and PGR effects on cell division. The experiments provided new insights which can serve as a basis to develop new cultivation practices to control fruit set and fruit development.