Pollen Development and Chilling Requirements in Apricot Cultivars

Apricot (Prunus armeniaca L.) flowers at the end of the winter but flower bud differentiation occurs the previous summer. During the winter, the flower bud enters dormancy and resumes growth prior to flowering. The time the flower bud remains dormant is genetically and also environmentally controlled and is a major factor determining the adaptation of particular cultivars to particular ecological conditions. In apricot, as in other temperate fruit species, chilling is required for buds to emerge from rest and chilling requirements vary greatly among cultivars. However, very little is known on the physiological changes underlying these events. To explore the relationship between pollen development and chilling requirements, anther and pollen development have been characterised in several apricot cultivars with different chilling requirements. For this purpose, sequentially fixed flower buds from dormancy to flowering were histochemically examined in two consecutive years. While the pattern of pollen development is highly conserved, differences in timing were observed among the different cultivars and years. These differences are discussed in relation to the chilling requirements for each cultivar. INTRODUCTION In most temperate fruit trees, flower buds differentiate the previous summer, enter dormancy during the winter and resume growth prior to flower the next spring. The time the flower bud remains dormant is genetically and also environmentally controlled and is a major factor determining the adaptation of species and cultivars to particular ecological conditions (Faust et al., 1997). In apricot, as in other temperate fruit species, chilling is required for buds to emerge from rest, although the mechanisms underpinning chilling are largely unknown. Thus, while chilling requirements vary greatly among cultivars (Layne et al., 1996), little is known on the physiological changes underlying these differences. Likewise, it is difficult to establish when flower buds have broken endodormancy and resume growth since no signs of development can be detected until budbreak several weeks later. In this work, in order to explore the relationship between pollen development and chilling requirements, anther and pollen development have been characterised in several apricot cultivars with different chilling requirements. MATERIALS AND METHODS Trees of several apricot cultivars (Currot, Moniqui and Paviot in 2006, and Canino, Corbato, Currot, Moniqui, Paviot and Luizet in 2007) were selected from an experimental orchard located at CITA in Zaragoza, Spain. To examine the internal