EVALUATING WINTER CHILLING OF KIWIFRUIT USING EXCISED CANES

Kiwifruit require a certain amount of winter chilling to flower adequa tely and produce a commercially acceptable yield, but precise temperat ure requirements have not been defined. Development of a reliable chil ling model has been hindered by the difficulty of obtaining data sets which relate bud break and flowering to temperature at specific times during winter. Preliminary work suggested that whole detached canes (1 5-20 buds) may be effective as experimental units. We used this techni que to investigate the temperature responses of kiwifruit during winte r. Canes collected from cool, moderate, and warm regions of New Zealan d were exposed to cool, ambient, or warm conditions for 27 d periods. The date of bud break was usually advanced by low temperatures during May, June and July and the proportion of bud break was increased. The exception, in both cases, was canes from Riwaka, which became unrespon sive to temperature by July. This is consistent with chilling being mo re advanced in the canes from this coolest site. Flowering was most af fected by low temperatures during late winter. The number of infloresc ences per winter bud was not affected by May temperatures but low temp eratures during June and July increased flowering. Comparison of the t emperature responses of canes from the three regions suggests that aut umn temperatures have an important effect on vine development during t he following spring. Thus the effects of autumn temperatures need to b e included in ''winter chilling'' models. These data will be used toge ther with the responses of entire vines to facilitate the development of chilling models.