ISHS Acta Horticulturae 175: Symposium on Physiology of Productivity of Subtropical and Tropical Tree Fruits
REPRODUCTIVE PHYSIOLOGY |
| Author: | M. Sedgley |
| Abstract:
Reproductive physiology is important in crop productivity as the economic product of a fruit tree is generally a reproductive structure. Microscopy techniques have been widely used to investigate reproductive physiology. Light microscopy of sectioned or cleared material can give information on all aspects of the reproductive cycle. Fluorescence microscopy is particularly useful for studies of pollen tube growth and scanning electron microscopy is an excellent tool for studying floral initiation and development. The major stages of the reproductive cycle which affect tree crop productivity are floral initiation and development, flowering, pollination, fruit set and fruit development. The evergreen tropical and subtropical tree fruit species have a relatively short period between floral initiation and anthesis with no dormant period as occurs in deciduous temperate fruit trees. Many species have outcrossing mechanisms such as dioecy (date palm), monoecy (lychee), andromonoecy (mango), dichogamy (avocado) or self incompatibility (macadamia). Fluorescence microscopy has confirmed that in macadamia the incompatible pollen tubes are inhibited in the upper style. Cultivars should be interplanted in the orchard for maximum yields. Insect pollinators are required for species with outcrossing mechanisms. This can be achieved by introducing honeybee hives into the orchard or by encouraging local insects which may be efficient pollinators. Flowering and pollen tube growth can be very temperature sensitive. In the avocado the temperature threshold varies between cultivars and is one of the reasons why Fuerte and Sharwil yield poorly in cool areas. Fuerte also has a high proportion of disorganised embryo sacs, as detected by light microscopy, and this may further reduce yield. Some species, such as mangosteen and some citrus, show parthenocarpic fruit development, and pollination and pollen transfer are not important considerations. In citrus overcropping and excessive seediness may be detrimental to yield and fruit quality. Premature fruit drop is a problem in a number of tropical and subtropical tree fruit species. Fruits shed within a month of flowering are generally unfertilised and reflect poor pollination. Fruits shed later than a month after flowering are fertilised and physiological factors such as competition or stress may be responsible. Fruit growth is generally sigmoidal and development of the characteristic fruit attributes does not occur until the final maturation stage. | |
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