The Effect of Temperature on Floral Behaviour, Pollen Tube Growth and Fruit Set in the Avocado

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Abstract
Avocado plants were kept in growth cabinets at 33°C day, 28°C night (33/28); 25°C day, 20°C night (25/20); and 17°C day, 12°C night (17/12), with a 12-h photoperiod and light intensity of 26000 1x. At 33/28 and 25/20 flowers opened in the afternoon as females and again the following morning as males (type B floral cycle) with some overlap of male and female stages at 25/20. At 17/12 very few flowers had a female stage, the majority opening once only as males. The duration of the flowering period decreased with a rise in temperature as did total number of flowers opening. Reproductive growth was inhibited in favour of vegetative growth at 33/28, as exhibited by smaller floral parts and abscission of buds and flowers. The rate of pollen tube growth increased with a rise in temperature, but abnormal growth was frequently observed at 33/28 and tubes failed to reach the ovary at 17/12. Endosperm and embryo development was observed to occur at 25/20 but not at 33/28 or 17/12 although a positive effect of pollination on fruit retention was evident at 33/28. This effect also occurred at 25/20 but not at 17/12. The most suitable temperature regime for floral behaviour, pollen tube growth and embryo development was 25/20.