Annals of Botany 30: 597-606, 1966
© 1966 Annals of Botany Company
RESEARCH-ARTICLE |
The Morphogenesis of Apple Buds
IV. The Effect of Fruit
East Mailing Research Station Kent
The course of development of spur buds on fruiting trees of ‘biennial’ and ‘regular’ apple varieties was followed throughout the season by dissection of successive samples of buds and the effect on bud development of de-fruiting trees at two different times in the season was recorded.
In the biennially fruiting variety Miller's Seedling, the pattern of bud development on fruiting trees was very similar to that in buds on non-fruiting trees which failed to form flowers following defoliation, as were the number and sizes of leaves preceding the bud in each instance. The failure to form flowers was associated with the occurrence of an 18-day plastochrone in buds, and it was concluded that on fruiting trees it was not due to a competitive effect of the fruit for nutrients.
This long plastochrone was not found in buds of de-blossomed trees of Miller's Seedling, and in trees de-fruited later in the season the buds immediately broke into a new flush of growth and at the same time the plastochrone was shortened. These results suggest that the long plastochrone was due to the inhibitory effect of fruit on the older primordia of the bud, an effect which did not occur until after the resting buds had begun to form. A phase with an 18-day plastochrone was also found in buds of another biennial variety, Laxton's Superb, but not in those of the regularly fruiting variety Sunset.
Developing fruitlets of biennial varieties caused bud-scales to form sooner and hastened their rate of development, possibly due to changes induced in the levels of a gibberellin-like apex factor in the buds. The rate of increase in number of bud-scales in the bud appeared to depend upon the extent to which the bud was affected by the primary leaves of the flower cluster and those of other clusters.
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