Abstract
The shape and aerial architecture of fruit trees have a direct impact, on production. ln order to take these traits into account in breeding programs a better understanding of their determinism is needed. This workaims at discriminating the factors that explain the diversity of shape and orientation observed among apricot-tree axes. Biomechanical modelling allows to quantify the link between the reorientation of axes and various traits of their development: dimensions, ramification, fruit-bearing, secondary growth and tension wood production. These paramcters werc measured during a growth season on one-year-old axes from three varieties exhibiting constrasted shapes. A mode] has been developed and evaluated by comparing simulations to observations. A good quantitative agreement can be reached provided the relevant mechanical assumptions arc made. The bending of axes in mainly determined by their slendemess. The load of fruits explains a part of the variability a.s well. Difforences in wood elasticity have a weak effect. The joined dynamics of loading and secondary growth explains differences in straightening at harvest. Tension wood implies an active straightening th .. t differs among varieties but doesn 't explain differences in shape. The determinism of active reorientations was studied by different complementary ways. This point is finally discussed, as well as the choice of the assumptions and the evaluation of the mechanical mode}, the scope of the results and possible applications.