Scanning Electron Microscope Observation of Abnormal Flowers and Their Frequency in Avocado Trees

Abstract

1. In order to determine avocado trees (Persea americana Mill.) flower morphology and abnormality percentages in Japan, flowers of the cultivars ‘Zutano’, ‘Bacon’ and ‘Fuerte’ were studied by scanning electron microscope (SEM) in 1981-1983.
2. The normal flower was as follows. 1) Perianth number was six. 2) There were nine stamens, three in each of three whorls, each anther with four pollen sacs. The third stamen whorl had a pair of nectaries attached to each filament. 3) The fourth (innermost) stamen whorl has changed its function, having evolved into three staminodes. 4) At the flower center is a primitive pistil.
3. Flower abnormality was most common in the pistil, including no pistil, short style, naked ovule, curved style, excess style number. The most common pistil abnormality was curved style, followed by naked ovule and style number, for all three cultivars. The maximum abnormality percentages were: Curved style, 87.8% in ‘Zutano’, naked ovule, 35.6% in ‘Fuerte’ more than one style, 11.1% in ‘Bacon’.
4. Stamen number ranged from 1 to 13, usually near the normal 9. Flowers abnormal in this respect varied among the three cvs. from 11.3 to 30.8% in 1981.
5. Number of perianth parts ranged from 3 to 11, with abnormal numbers usually a little greater than the normal 6. Abnormal flowers varied from 0.7 to 15.3% in 1982, among the three cvs.
6. Abnormalities involving these various flower parts were observed in all combinations, including single flower abnormal for all of: Perianth parts plus stamen number plus style number plus curved style plus naked ovule.
7. In terms of flowering date, perianth and stamen abnormalities were more common in early and mid-season flowers, whereas late bloom was associated more often with pistil abnormalities.