Bonhomme, M., U.A. Bioclimatologie, PIAF, INRA Domaine de Crouelle, 234, avenue du Brezet, 63039 Clermont-Ferrand Cedex, France
Rajeau, R., U.A. Bioclimatologie, PIAF, INRA Domaine de Crouelle, 234, avenue du Brezet, 63039 Clermont-Ferrand Cedex, France
Richard, J.P., U.A. Bioclimatologie, PIAF, INRA Domaine de Crouelle, 234, avenue du Brezet, 63039 Clermont-Ferrand Cedex, France
Gendraud, M., U.A. Bioclimatologie, PIAF, Université Blaise Pascal, F63177 Aubière, France
Erez, A., Institute of Hort., Volcani Center, P.O.Box 6, Bet Dagan 50250, Israel

To analyse the influence of photoperiod and temperature on the evolution of dormancy in vegetative and floral buds, the following treatments of various combinations of daylength and temperature were examined: Long Day Warm (LDW); Short Day Warm (SDW) and Short Day Cold (SDC). These conditions were applied to container grown peach trees on August 1, 1995 in Clermont Ferrand. Endodormancy and paradormancy were distinguished by measuring of the growth capacity of the buds by the biochemical "nucleotides" test, by the biological "single node cuttings" test for vegetative buds and by growth of the primordia in intact floral buds. As possible basis of short distance inhibition of bud growth, the sink strength of the buds were also investigated by measuring their intracellular pH. Results showed that temperature, but not photoperiod, strongly determined the dormancy evolution of both vegetative and floral buds. At temperatures above 20°C, the existing endodormancy persisted, whereas at temperatures between 10 and 18°C the global inhibition decreased but, in the vegetative buds, did not disappear after 2 months in the SDC treatment. In the floral buds, it seemed that growth could start immediately at high rate after breaking endodormancy. The results of the "nucleotides" test and observation of a weak growth under the LDW and SDW treatments were not totally consistent. Under SDW treatment, the intrinsic growth capacity of floral buds showed cyclical variations the nature of which is not clear. Intracellular pH values of the different tissues were influenced by both temperature and photoperiod. Vegetative buds showed mostly lower values in short day treatments while flower bud values were reduced by low temperature. The resulting potential sink strengths could not, by themselves, be the basis of the persisting inhibition of the vegetative buds whatever the treatment.