Abstract
1. In order to clarify the time of flower bud differentiation and subsequent development in avocado trees (Persea americana Mill.) in Japan, flower buds of the cultivars, ‘Zutano’ (6 to 7-year-old), ‘Jalna’ (5-year-old) and ‘Fuerte’ (20 to 28-year-old) were studied morphologically using a stereoscope and a scanning electron microscope (SEM) during 1979-81.2. In 1979-80, flower bud differentiation was observed on November 11 in ‘Zutano’ and ‘Fuerte’, and on November 25 in ‘Jalna’. In 1980-81, the differentiation was observed on November 9 in ‘Fuerte’, and on November 23 in ‘Zutano’ and ‘Jalna’. As the results of this two-time examination, it was shown that time of flower bud differentiation in the south-western warm area of Japan was in November in the three cultivars.3. The stages and times of flower bud development were as follows:1) No differentiation (flatness of growing point) ... late in October2) Differentiation of flower bud (protuberance of growing point) ... November3) Perianth formation, pistil and stamen primordia formation ... early in December4) Anther dehiscence valve and staminodium formation ... middle in January5) Pollen grain and ovule formation ... early in February6) Carpel suture and floral formation ... middle in March4. In the south-western warm area of Japan, time of flower bud differentiation in avocado trees was later than in deciduous fruit trees, and earlier than in evergreen fruit trees (except loquat).5. In 1980-81, flower bud development was inhibited for a short period by the low temperatures of winter, which were lower in the avocado orchard than in 1979-80.
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