Almond flower development: Floral initiation and organogenesis

Scanning electron microscopy was used to examine almond [Prunus dulcis (Mil l.) D.A. Webb (syn. Prunus amygdalus Batsch, Amygdalus communis L.)] flower bud development for three cultivars (Nonpareil, Carmel, and Butte) from fo ur California locations (which span the range of almond production in Calif ornia) for 2 years, and for 'Nonpareil' in a single location for a third ye ar. The objectives were to document timing of floral developmental events a nd to better understand the extent of variation that exists within and amon g cultivars, locations, and years. Results indicated that the time of flora l initiation relative to hull split varied among cultivars. Median time for floral initiation in 'Nonpareil' was more than 3 weeks after the onset of hull split. For 'Butte' and 'Carmel', median time of floral initiation prec eded the onset of hull split. Extensive variation in the timing of bud deve lopment events within a cultivar was apparent. Timing of developmental even ts varied among locations, but no patterns emerged consistent with the nort h to south range which spanned 4 degrees 15' latitude and 520 km. Among yea rs, development occurred earliest in 1997, a relatively warm year, and was delayed in 1998 and 1999, relatively cool years. Results indicate an earlie r onset of floral initiation than reported in the classical literature on t he subject.