Actinidia chinensis: physiological and productive performances under different irrigation restitutions

Yellow flesh kiwi fruit production normally follows protocols based on the green species, A. deliciosa, often resulting in low yields, attributable to small sized fruit, meaning A. chinensis seems more susceptible to water limitations. Understanding the species physiology and fruit vascular flows may help determine this crop’s evapotranspiration needs, to efficiently obtain satisfactory harvests. The presented work results from a 3-year trial (2019-2020-2021), where control irrigation vines were compared with deficit-irrigated and over-irrigated vines. Midday physiology, including plant water relations, leaf gas exchanges and fruit vascular flows were analysed, along with harvest parameters and dry matter content. Irrigation treatments influenced the vines’ responses only when soil water content was below certain levels, reflecting sensitivity of the crop to water changes in the soil. Although no significant differences were found in harvest parameters, dry matter content was higher for the less irrigated fruit. The less irrigated treatment performed less better, than the control and the over-irrigated, especially when water supply did not fulfil fruit transpiration. This occurred during the berry development phase (around 1 month after full bloom), a critical period during which the fruit has very high transpiration rates, which passively call photosynthates (phloem inflow) to provide energy for cell division. Fruit transpiration appears to influence phloem inflow during most of the season, even until 1 month before harvest, however the initial phases of fruit development and growth are pivotal for final yield. Vascular flows allowed to unveil a typical simplasmic behaviour in the early stages of berry development, meaning the microenvironment is intensely influencing fruit behaviour. Irrigation must respond to the needs of young fruit, taking into account soil water content and the phenological phase. The use of sensors, plant based and environmental, is an important technique for determining the necessary water volumes for yellow kiwi fruit.