Fruit vascular flows in yellow-fleshed kiwi reveal tight relations between water availability and fruit growth potential, until harvest

Yellow-fleshed kiwifruit production guidelines normally follow protocols based on the green-fleshed species, A. deliciosa, often resulting in low yields, reduced dry matter and small fruit size, as A. chinensis seems more susceptible to water limitations. Clarifying this species fruit vascular flows may help improve yields, and fruit size, by satisfactorily meeting its irrigation needs. This 3-year trial (2019-2021) compared 100 % with deficitirrigated and over-irrigated vines. Plant water relations, leaf gas exchanges and fruit vascular flows were measured at midday during the season, and fruit were harvested and assessed for dry matter content. Irrigation influenced vine responses only when soil water content dropped below 25-30 %, reflecting the sensitivity of this crop to soil water changes. Although no differences were found for yield, dry matter content was higher for the least irrigated fruit, but overall vine performance in this treatment was limited throughout the study, in particular during the rapid growth phase (e.g., ca 1 month after full bloom), when very high fruit transpiration rates energize passive phloem unloading, to support fruit parenchyma cell division and expansion. Unlike A. deliciosa, A. chinensis appears to maintain fruit transpiration and associated phloem unloading later into the season. The symplasmic unloading in the early stages of berry development reveals a strong effect on fruit development by its microenvironment, thus irrigation must be carefully gauged to the needs of developing fruit, accounting for soil water content and the phenological phase. Plant and environmental sensors are quite important for determining the necessary water volumes for yellow-fleshed kiwifruit.