Winter cold tollerance of kiwifruit. A survey after winter frost injury in Northern Italy

Quantitative flowering of kiwifruit (Actinidia deliciosa (A. Chev.) C. F. Liang et A. R. Ferguson var. deliciosa) was investigated in 25 North Italian kiwifruit orchards to evaluate frost resistance following a severe cold spell in January 1985, when air temperatures dropped as low as - 23 ° C. The percentage of fruitful shoots in female cultivar 'Hayward' began to decrease at -11°C; at about -18°C very few reproductive buds burst the following spring. As temperatures decreased, the proportion of vegetative shoots, arising from meristems in the basal axils of winter buds, increased. The male cultivar, 'Matua' reacted in a similar way to 'Hayward', but 'Matua' was more tolerant to frost injury. The same reduction in flowering shoots, resulting from a fall in temperature, was obtained at about - 1.2 to -1.8 °C lower in male than in female plants in the range from -II to -18°C. In no case was plant death observed. Acutely damaged plants were capable of regrowth from adventitious buds either of the leaders or of the trunk.