Bud dormancy of apple and pear in relation to the temperature during the growth period

In 2 experiments, apple and pear trees were grown in growth chambers and air conditioned greenhouses at a range of constant temperatures from 9 to 25° C during spring and summer. After the dormant buds had received a marginal chilling-period, bud break and leaf development were studied. A tendency was observed for the dormancy to be deeper when the temperature at which the buds were formed had been higher. The maximum retardation of bud break was observed in buds formed at 18 and 21° C. The hypothesis is put forward that the phenomenon of “delayed foliation” is not only due to insufficient chilling during winter but also to high temperatures during the preceding summer.