Influence of three contrasted climatic conditions on endodormant vegetative and floral peach buds: analyses of their intrinsic growth capacity and their potential sink strength compared with adjacent tissues

Three treatments with various temperature-photoperiod combinations (LDW: long-day warm; SDW: short-day warm; SDC: short-day cold) were applied to endodormant vegetative and floral peach buds. In order to analyze the effect of these factors on their dormancy state, the following complementary methods were used: (1) for vegetative buds, the ‘single-node cutting' test that measures the growth capacity of the buds connected to the shoot and integrates endo- and short-distance paradormancy; (2) for floral buds, growth rate of the primordia that integrates endo- and all paradormancy. For both kinds of buds: (3) the ‘nucleotides' test that reveals the intrinsic growth capacity of the isolated bud, i.e. endodormancy, by measuring the potential of converting adenosine to non-adenylic nucleotides; (4) the intracellular pH measurement of primordia and adjacent tissues (cushion and shoot) which is supposed to reflect their relative sink strength for nutrients and the competition between them. This is a possible element of short-distance paradormancy.

Temperature, and not photoperiod, strongly determined the evolution of dormancy in vegetative and floral buds. Exposure to temperatures >20°C, prevented the buds recovering any intrinsic growth capacity, but they did it with notable rapidity under 10–18°C temperature regime (SDC). After one month, under all treatments, consistent with the poor chilling effect (nil under LDW and SDW, one third of the normal requirement of chilling units computed with the ‘dynamic' model under SDC), a residual inhibition of the vegetative bud growth was shown to exist at the cutting level. It must be hypothesized as strong short-distance paradormancy. In the floral buds, growth of the primordia started shortly after exposure to SDC conditions. This is possible provided it is assumed that only very weak residual short-distance paradormancy, if any, remained. Intracellular pH values of the studied tissues were influenced by temperature and photoperiod, but the corresponding gradients of the potential sink strength did not fit well with the paradormancy patterns that had been assumed for the vegetative and floral buds, especially under SDC treatment.