Bud development and floral morphogenesis in four apple cultivars

Buds were sampled from non-flowering spurs that had developed on 1 year-old wood of four apple (Malus domestica Borkh.) cultivars during the 1998-99 growing season in order to determine the effect of cultivar on appendage formation, doming and flower morphogenesis. Cultivars differed in their pattern of appendage formation over time. The rate of appendage formation was highest in 'Fuji' and 'Pacific Rose™' and lowest in 'Braeburn' during the first 60 d after bloom (DAB). A high proportion of buds were floral in all cultivars at the end of the growing season (75-100% depending on cultivar). However, the probability of observing doming was never greater than 0.13, indicating that flower morphogenesis proceeded rapidly once buds were committed to floral development. The four cultivars each exhibited a unique pattern of floral development, as determined by fitting response probabilities to each of five ordinal stages of development with time. Doming occurred significantly earlier in 'Fuji' buds (peaking 86 DAB) than in buds of the other cultivars (peaking 104-112 DAB). Doming was initiated at the same time in buds of 'Braeburn', 'Royal Gala' and 'Pacific Rose™, but was completed earlier in 'Braeburn' than in 'Royal Gala'. The timing of floral commitment was not related either to the time of flowering, or to the time of fruit maturity of the cultivar. These observations indicate that the timing of specific events during flower morphogenesis differed between cultivars.