Avocado trees of a range of cultivars growing in Darwin, northern Australia (average yearly maximum 33°C, minimum 23°C), were observed for flower and shoot development. Terminal buds of the cultivars 'Fuerte', 'Rincon' and 'Edranol' sampled in July were not floral. Buds which did not burst were sampled in September and they contained developing flowers with perianth primordia. Vegetative extension growth resulted from laterals proximal to the inhibited terminal buds.Avocado trees of the cultivars 'Fuerte' and 'Hass' which had initiated floral buds were transferred to controlled environment chambers with 33°C day, 23°C night (33]23) or 25°C day, 15°C night (25/15) with a 12-h photoperiod and photon flux density of 400 umol m -2 s -1 (400--700 nm). At 33/23 the trees had fewer flowers and a shorter flowering period than at 25115. Inhibited floral buds and lateral vegetative extension resulted at 33•23, as observed in northern Australia. The unburst buds had developing flowers with perianth and stamen primordia.The controlled environment experiments showed that the abnormal flushing behaviour of Mexican-and Guatemalan-type avocados growing in northern Australia was due to high temperature. Floral development was inhibited at the stage of stamen differentiation.
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