BUDBREAK NUMBER AS SELECTION CRITERION FOR BREEDING APPLES ADAPTED TO MILD WINTER CLIMATIC CONDITIONS: A REVIEW

This paper is a review of experiments conducted over a period of five years to investigate budbreak number (NB) as a practical criterion of selection for adaptability of apples (Malus x domestica Borkh.) to mild winter conditions.
Apple trees planted in the Western Cape of South Africa develop prolonged dormancy symptoms, such as poor budbreak and extended flowering periods, because winter temperatures are not cold enough to satisfy the inherent chilling requirement of commercial cultivars.
Variation within and between adult and juvenile seedling families was investigated and the genetic control of different traits involved was assessed, as well as direct and correlated responses to selection.
In general, within family variance was higher than between families for all traits.
Responses to two-way selection demonstrate that there is utilizable genetic variance in NB present within seedling families and NB may be used successfully as an early screening method for increased budbreak in adult trees.
Correlated responses to selection for NB were shown to include improved uniformity and position of budbreak and increased number and length of side shoots.
The NB of intact one-year-old shoots under prevailing sub-optimal winter conditions is proposed as criterion of selection for improvement of climatic adaptation.
Combined selection utilizing genetic variation between and within crosses is the selection method proposed.

XI Eucarpia Symposium on Fruit Breeding and Genetics

I.F. Labuschagné

Malus x domestica, fruit breeding, climatic adaptation, chilling requirement, prolonged dormancy symptoms, two-way selection, selection response, broad sense heritability

https://doi.org/10.17660/ActaHortic.2004.663.140