ISHS Acta Horticulturae 441: V Temperate Zone Fruit in the Tropics and Subtropics
AN INVESTIGATION OF THE CHILLING REQUIREMENT OF SOME APPLE CULTIVARS IN THE PO VALLEY, 1992–1996 |
| Author: | G.A. Finetto |
| Abstract:
Evaluation of the chilling requirement in temperate fruits has mainly been done under controlled climatic conditions, and responses often differ when these species are cultivated in tropical and subtropical zones. In order to provide more information on this matter some mid-chilling apple cultivars planted in 1985 were tested. During the winter season for four years, 30 one-year-old twigs and 30 shoots with spurs were taken from the trees every week and kept with their bases in water in a growth chamber for 20 days at 21°C. Apical and lateral buds were both counted and evaluated as to percentage of the total that grew and as to bud development stage. The temperatures during the winters were recorded and both the Richardson and Crossa-Raynaud formulae were tested, and GDH also was calculated. The onset of bud break and the end of rest in the one-year-old shoots and in the spurs were assessed by means of the ratio between the chilling units (CU), the chilling hours (CH), and GDH and by the above mentioned indexes. Although significant regressions were observed between the indexes and CU, CH and GDH throughout the years the prediction of end of the rest was generally best when the time was considered rather than the quantity of chilling. The two different buds varied in length of dormancy within cultivars; this can modify the value of their chilling requirement. In the Po Valley the chilling requirement of apple cultivars should be evaluated both by the traditional formulae and by other indexes in order to obtain best results. | |
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