The influence of water deficit and re-watering on flower bud morphogenesis in young apricot trees (Prunus armeniaca L.)

In deciduous fruit species, as well as in apricot, floral bud initiation, differentiation and organogenesis take place during the summer season that precedes anthesis. A number of factors (environmental conditions, cultural practices, abiotic stresses) have been identified as important triggers able to modify the regularity of floral differentiation. The water availability represents a crucial key factor, particularly under Mediterranean climates characterized by long drought periods. This investigation aimed to assess the influence of summer water deficit and re-watering treatments on floral morphogenesis, growth and quality of flower buds in apricot. Trials were carried out on two-year-old potted trees ('Portici') grown at the research station of University of Pisa. Plants were divided into three uniform groups: the first one was watered daily maintaining soil water content around 90% of field capacity, whereas second and third ones were subjected, in June or July, to 30 days of imposed water deficit followed to re-watering. In order to determine the evolution of floral bud differentiation, prior, during and after the imposed water stress, histological analyses were carried out. From autumn to spring, qualitative traits of flower buds (growth, anomalies) were also analyzed. Midday stem water potential was used to determining water status, and leaf gas exchanges were measured during trials. Both water stress periods affected the floral differentiation leading to a temporary shutdown. The plants stressed in June were able to recover the development of meristematic apices already after two weeks from the regular re-watering, while those stressed in July showed a strong delay up to the end of summer. As a consequence, variations in bud size and flower anomalies were observed. Results confirm that water stress may play an important role in flower bud differentiation and development influencing the quality of flower buds.