INFLUENCE OF GLASSHOUSE CONDITIONS ON FLOWER BEHAVIOR OF HASS AND ANAHEIM AVOCADOS

Abstract

Summary The first opening of flowers of tip-grafted trees of the Hass and Anaheim varieties in the glasshouse began in early forenoon and the second opening in early afternoon. The situation was reversed with comparable trees and large bearing trees continuously outside. In the latter, first opening flowers appeared initially from noon until late afternoon, apparently fluctuating with the temperature. Night temperatures may be very important, since trees placed in the glasshouse for the night only behaved essentially as the trees under continuous glasshouse conditions, and trees placed in the glasshouse for the day only behaved essentially as trees continuously outside. The double opening of individual avocado flowers has been described by Stout (1923, 1933), Robinson and Savage (1926), and others. The flowers are dichogamous. At first opening, termed stage I when complete, the petals and stamens art extremely reflexed and the pistil prominently exposed. The flowers are then female in function and no pollen is shed. On the same day the flowers close and remain closed until the following day when they reopen into stage II. The petals are then parted but not reflexed, three of the stamens are erect against the pistil, functional pollen is shed but the stigma is usually withered and no longer receptive to pollen. The rhythmic nature of the double opening also has been investigated and many varieties have been classified into A and B groups on the following basis. A. Varieties such as Dickinson, supposed to have stage I flowers in the morning and stage II flowers in the afternoon, and B. Varieties such as Fuerte, supposed to have stage II flowers in the morning and stage I flowers in the afternoon. Variations in flower opening of given varieties has been discussed to some extent by the above cited and Nirody (1922), Stout and Savage (1925), and Robinson (1931). They reported that inclement weather and in particular low temperatures tended to change the blooming cycle. Strict synchronism of the blooming stages may not occur so that stage I and stage II flowers may open in a single variety at a given time. Time of opening may fluctuate considerably and stage I flowers may not appear at all on some days. In many California locations irregular behavior appears to be quite normal. Lyon was reported by Lammerts (1942) as having flowers which opened only once. Pollen was shed on individual flowers while their pistils appeared receptive, after the manner