Résumé
Well-feathered apple trees are essential for commercial orchards to
optimize yields. However, most cultivars do not form these sylleptic
branches readily in commercial nurseries due to high apical dominance.
Several treatments exist to promote their formation in the nurseries, one
of which is heading. However, not all cultivars are expected to react
similarly to these treatments. We studied the branching response of 155
genotypes following heading and its relation to other architectural traits
as a function of the cultivar’s genetic background. Trees were grown for
two consecutive years after grafting in a nursery, and the main axes were
headed in the winter following growth in year 1. After heading, a single
shoot was retained when growth resumed in the second year. Plant
architectural traits such as growth of the main shoot, internode length,
sylleptic branching, etc. were measured before and after heading and were
statistically compared using a mixed model. This model showed the effect
of heading for all architectural traits studied. In addition significant
genotype and genotype × treatment interactions were found. In general,
genotypes that showed a more vigorous growth during the first year also
reacted more vigorously to heading. Accounting for the genetic
substructure of this collection, no clear distinction in tree response
could be found except in a small group of individuals that belonged to an
F1 mapping population. This study shows that heading is not favorable for
all genotypes to promote sufficient sylleptic branching and that other
methods are needed to promote branching in these accessions.