QTL analysis for growth and branching traits annually assessed along the trunk of three-year-old apple hybrids

UMR DAP équipe AFEF;

International audience

Inglés. In fruit trees, architectural traits are generally controlled through the use of size-controlling rootstocks, pruning, and training. However, a better knowledge of the genetic determinisms of these traits could allow their introduction in selection schemes and reduce the costs of training practices. Within this context, in a previous study, we investigated the genetic determinisms of architectural traits in a one-yearold apple progeny through QTL mapping. As a continuation, the present study investigated the same progeny in the two following years. Herein, results are presented for growth and branching traits annually assessed along the trunk of three-year-old apple hybrids. Several QTL were detected for both primary and secondary growth traits, such as length and bottom diameter of the third annual shoot (AS) on linkage group (LG) 6, or mean internode length of the first and second AS on LG3 and LG14 respectively. Considering branching traits, QTLs were detected only on the first AS. A QTL was detected on LG8 for the number of latent buds, after the first year of growth. In the second year, since proleptic shoots developed from these latent buds, the same QTL was detected for the number of the proleptic shoots. Traits were also cumulated over the successive years of growth, which allowed us (i) to confirm a QTL already detected for mean internode length, (ii) to find new QTL for AS length, mean internode length, and the total number of axillary shoots. Revealing new QTLs when the traits were cumulated over years suggests a more precise estimation of the genotypic values due to a possible smoothing of environmental effects. Nevertheless, in these results, QTL were detected mostly for traits considered on the first or second AS. This pattern is likely to result from ontogenetic gradients responsible for a decrease in expression and variability of growth traits