Apple genotypes exhibit specific architectural and physiological profiles linked to their flowering behaviours

Large genotypic variability is observed in flowering regularity among apple genotypes. Previous studies have suggested that floral induction (FI) is determined by competition for carbohydrates and/or hormone signaling. Moreover, the large variability has been associated with architectural traits. However, the part of variability that could be explained by either tree architecture or physiology (i.e. carbon and hormone) is still not clear. This study aimed at deciphering the respective effect of architectural and physiological traits on FI in apple trees. It was carried out on six genotypes with contrasting architectures. The demography of shoot types produced in each year and the flowering and production patterns were observed over six years. Meanwhile, flowering and production patterns were characterized by different indices. During two successive years, non-structural carbohydrate content (starch, sorbitol, sucrose, hexoses) in leaf, stem and meristems and hormonal contents (gibberellins, cytokinins, auxin and abscisic acid) in meristems were quantified. Groups of genotypes were defined based on architecture and production traits using principle component analysis. Based on multi-step regression analyses, cytokinins, gibberellins, starch content in leaves and the proportion of long shoots were implicated in FI determination. However, each of these variables had a different weight in a linear model predictive of FI and their weight depended on the genotype. Our results therefore suggested that, within a common model, each genotype has a specific architectural and physiological profile linked to its flowering behaviour. Finally, this study provided new clues to further understand the determinisms of genotypic variability in FI.