Effects of shoot bending on lateral fate and hydraulics: invariant and changing traits across five apple genotypes

The aim of this work was to study the variability of physiological responses to bending and the relationship with hydraulic conductance of the sap pathway to the laterals for five apple genotypes. The study focuses on the fate of the laterals. The genetic variability of bending can have two sources: a genetic variability of stem geometry which can lead to differences in mechanical state; and a genetic variability of sensitivity to bending. Since the aim was to check if some genetic variability of sensitivity to bending exists, the genetic variability of shoot geometry was taken into account. To do so, bending was controlled by imposing different bending intensities using guides of different curvature conferring a similar level of deformation to the five genotypes. Bending was done either in the proximal zone or in the distal zone of shoots, in June and in the following winter, respectively. A Principal Component Analysis comparing upright and bent shoots revealed that bending in the proximal zone stimulated vegetative growth of buds which would otherwise stay latent. A second Principal Component Analysis restricted to bent shoots revealed that bending increased the abortion of laterals in the lower face of the shoots. The abortion phenomenon was to the detriment of sylleptic laterals or of inflorescence, depending on the genotype. There was a strong effect of position around the shoot on within-shoot hydraulics. Hydraulic conductance was significantly decreased in the lower face of the shoot bent in winter. This result suggested a causal relationship between this phenomenon and lateral abortion.