Shoot Development in Citrus sinensis L. (Washington Navel Orange). I. Floral and Inflorescence Ontogeny

Floral and inflorescence development was studied in Citrus sinensis (L.) Osbeck (Washington navel orange) to establish the pattern and timing of organogenesis. Morphological characters were used to select dormant flowering and vegetative shoots. Bud break occurred on flowering shoots 3-4 wk earlier than on vegetative shoots. Initiation of sepals and petals followed the 3/8 phyllotactic pattern. These fleshy organs tightly enclose the whorl of numerous stamens and the two whorls of carpels, which form the "navel." Organogenesis from sepal to carpel initiation required 2 wk, and anthesis, another 3 mo. Within the cymose inflorescence, development of the terminal flower was followed by the simultaneous initiation of lateral flowering shoots in the axils of six to seven foliar leaves. The terminal flower was always the most advanced in development, and the position 2 flower, the least. Basipetally, the other lateral floral meristems were gradually released from this apparent apical dominance, which may explain observed positional effects on fruit persistence.