THE RESPONSE OF BUD BREAK AND FLOWERING TO COOL WINTER TEMPERATURES IN KIWIFRUIT (ACTINIDIA-DELICIOSA)

A range of temperatures (7 degrees C, 10 degrees C or 13 degrees C mea n) were imposed under controlled conditions on four year old, containe r-grown 'Hayward' kiwifruit vines. The treatments were applied for per iods of from one to four months during the dormant period from May to September (Southern Hemisphere). Following these treatments the vines were held at a ''forcing'' temperature of 16 degrees C mean until flow ering. The objective was to define the response of bud break and flowe ring in spring to temperatures experienced during the preceding winter . Cool winter temperatures dramatically increased flower numbers, incr eased the proportion of bud break, advanced the day of bud break, and increased the duration from bud break to flowering. These responses we re much larger between 13 degrees C and 10 degrees C than they were be tween 10 degrees C and 7 degrees C. For any treatment duration, the te mperature imposed during dormancy had no effect on the time of floweri ng. Two months at cool temperatures produced the greatest number of fl owers per winter bud, with reduced numbers at three and four months. T he proportion of winter buds that produced shoots showed a similar res ponse. The Richardson chill unit is frequently used to describe the ef fects of winter chilling on kiwifruit. It proved unreliable as an inde x to integrate the effects of temperature and time on any of the devel opmental variables monitored in this experiment.