The Environmental Control of Cold Acclimation in Apple

Abstract

The role of photoperiod and temnperature in the cold ac-climation of living Haralson apple (Pyrus malus L.) bark was studied in the autumn under field conditions in Minne-sota. Whole trees, or different parts of the same tree, were exposed to either natural conditions, artifically lengthened days, or artificially warmed iiights, or they were subjected to manual leaf removal. The results indicate that acclima-tion occurs in two stages which are induced by short days and frost (or low temperature), respectively. Leaves were stimulated by short days to produce translocatable sub-stance(s) which promoted cold acclimation of the living bark. Leaves of plants grown under long days were the source of a translocatable substance(s) which inhibited acclimation. The second stage of hardiness, induced by frost (or low tenmperature), did not involve translocatable factors.