Influence of different seasonal light availability on flower bud quality in cv Tirynthos (Prunus armeniaca L.).

Floral morphogenesis is known to be affected by environmental parameters, among which light plays a primary role. Light-mediated nutritional factors may also affect flower development. Flower quality accounts for determines the developmental ability of the fruit. The aim of this study was to investigate the role of light in determining flower bud quality. The investigation was carried out on Y-trained apricot trees (cv Tirynthos). Light interception and distribution within the canopy were measured during the whole growing season. Throughout floral morphogenesis the nutritional status (i.e. starch and soluble carbohydrates) of flower buds and shoots formed under different light irradiance was characterized. At anthesis, flower structure (i.e. pistil size and stomatal density and size on sepals) and functionality (i.e. gas exchanges) were checked for the lighted and shaded canopy zones. These characteristics were then related to fruit set and growth ability. The nutritional status of flower buds proved to be influenced by the fruiting shoot type, as well as by light availability in the different canopy zones. In general, flower buds which developed on spurs and at the higher light irradiance levels had higher carbohydrate reserves. Light also had a positive effect on flower bud number per fruiting shoot. At anthesis some morphological characters of the flower, i.e. pistil length and stornata size, proved different in the two canopy zones, while flower gas exchanges did not. Fruit set and growth rate were lower in the shaded zone of the canopy, where the quality of the floral bud was generally poorer. Light availability during floral morphogenesis affects flower bud quality in terms of nutritional status. The morphogenetic effect of light can also be important in determining flower quality. This may result in different fruit set ability and fruit developmental potential.