Kiwifruit (Actinidia deliciosa and A. chinensis) is an important commercial crop in New Zealand and is grown primarily in the Bay of Plenty but spreads from Kerikeri in the north to Nelson in the south. Irrigation is often necessary due to unreliable rainfall, soils with poor water holding capacity, and root growth limitations. Kiwifruit is native to the mountains of southern China and has evolved in a high humidity area with regular annual rainfall of 1050 to 1950 mm (Buwalda and Smith, 1990). These authors found that green kiwifruit (A. deliciosa var. deliciosa ‘Hayward’) has a high transpiration rate with poor stomatal control. Green et al. (1989) reported that A. deliciosa transpires at night and this could account for up to 30% of all the water used for any given 24-h period. However, Gucci et al. (1997) reported that A. deliciosa does not demonstrate low midday leaf water potential values under water deficit as effective stomatal closure allows water conservation. But Chartzoulakis et al. (1993) reported that A. deliciosa seedlings showed poor control of transpiration even though there was a reduction in stomatal conductance (gs) and suggested that this species has poor epidermal control of water loss through leaky stomata or an insufficient cutinisation of the epidermis.
Conflicting reports on the ability of kiwifruit to reduce water loss under water deficit warranted investigation. Most of the information on the water relations of kiwifruit relates to A. deliciosa (e.g., Judd et al., 1989; Miller et al., 1998; Reid et al., 1996). We were interested in obtaining information on the water stress physiology of gold kiwifruit (A. chinensis Planch. var. chinensis ‘HORT16A’) as it has been extensively planted in recent years on many sites in New Zealand where soil water holding capacity is low, rainfall is variable, and periodic soil water deficits may develop.
Gold kiwifruit differs from green in that its dormancy break is ≈1 month earlier, and tends to have a higher crop load and a higher percentage of dry matter (DM) in the fruit. It is harvested earlier than green kiwifruit by up to 6 weeks. The higher fruit DM gives gold kiwifruit a better taste.
We studied the impact of reduced irrigation on pot-grown A. chinensis with specific interest in its physiological responses in terms of water relations, gas exchange parameters, and growth. Our experimental design provided the opportunity of studying the effect of water stress history on plant physiological responses to water stress that are sometimes difficult to establish in the field. We wished to test the hypothesis that kiwifruit demonstrates physiological adaptation to water stress following a previous stress episode.
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