Flower bud development of almond cultivars based on three different methods

Flower bud development of fruit trees plays a key role in their climatic adaptation. It is closely related to dormancy release that determines winter frost susceptibility. Detailed characterisation of flower bud development of 25 almond (Prunus amygdalus L. Batsch) accessions representing wide range of flowering times have been performed by microsporogenesis and pistil growth studies for 3 years. Six developmental stages were distinguished in the process of microsporogenesis, while pistil development could be classified into four phases. The examined cultivars showed significant differences in the length and occurrence of microspore developmental stages and year effect was observed. On the basis of the length of microsporogenesis stages, cultivars were clustered into five main groups. The shortest periods of archesporium and microsporogenesis as a sum were detected in accessions 'Eriane', '5/15' and '1/7' (with an average of 20 and 138 days in all three), while the longest ones were determined in 'Constanti' and 'Vairo' (65 and 160 days in both), respectively. The increment of pistil length was suspended during the dormancy period and after dormancy release, it was accelerated first at a slow rate followed by a few days of rapid growth prior to blooming. In order to determine the date of endodormancy release, these three methods - microsporogenesis, pistil length studies, and forcing of shoots - were analysed. All methods revealed significant differences among accessions. The dormancy release estimated by microsporogenesis studies showed the highest variability among the three methods used.