Water use efficiency of pergola-trained kiwifruit plants.

Water use efficiency (WUE) was evaluated on pergola-trained mature kiwifruit plants (cv. Hayward) spaced at 4 x 4 m in an orchard located in Southern Italy (40°20' N, 16°48' E). During the growing season leaf area index (LAI) evolution was evaluated and the exposed/shaded leaves ratio estimated. Leaf and fruit gas exchange was measured with a portable open system (ADC-LCA4). LAI evolution was rapid and reached its maximum value, i.e. 3.7, 80 days after bud burst, when 60% of the leaf surface was shaded. During the growing season shaded leaves showed 95% lower CO2 assimilation and 60% lower transpiration than those exposed. Water consumption of fruits during the season varied between 0.2 and 0.6 m3 ha-1 d-1, with the highest values during the first 30 days from fruit set. The daily carbon balance of shaded leaves was negative, so that these leaves were not a source but rather a sink for the plant.