Abstract. We investigated the effects of partial rootzone drying (PRD) and rootstock vigour on water relations, and vegetative and productive performance of 'Pink Lady' apple (Malus domestica Borkh.) trees in central Sicily. In a first field trial, trees on MM.106 rootstock were subjected to: Conventional irrigation (CI), maintaining soil moisture above 80% of field capacity; PRD irrigation, where only one alternated side of the rootzone received 50% of the CI irrigation water; and continuous deficit irrigation (DI), where 50% of the CI water was equally applied to both sides of the rootzone. In a second trial, trees on M.9 or MM.106 were subjected to CI and PRD irrigation. PRD reduced stomatal conductance (g s ) more consistently in trees on MM.106 than in trees on M.9, but maintained relative water content (RWC) to the levels of CI. DI induced greater g s reductions than PRD and lower RWC than CI and PRD. Rootstock vigour did not influence plant response to irrigation strategy. PRD induced some reduction in fruit number but no change in yields and fruit quality compared with CI, whereas DI reduced fruit size and marketable yields. Significant reductions in shoot and leaf growth were induced by DI, whereas only leaf growth was affected by PRD. Our observations indicate that responses induced by PRD are due to a combination of the amount and way of applying water, and not just to reductions in irrigation volumes, suggesting a possible use of PRD for increasing apple water-use efficiency in Mediterranean environments.
We used (13)CO(2) tracing and source-sink manipulation to determine if fruiting shoots of peach (Prunus persica (L.) Batsch) trees are autonomous or if they import carbon from neighboring shoots, and if the degree of shoot autonomy is influenced by the source-sink relationship of the shoot. In three experiments, leaf to fruit ratio (L:F) of selected fruiting shoots was moderately (2005 and 2006) or strongly (complete sink removal, 2006) altered to either enhance or inhibit movement of carbon from (13)C-labeled fruiting shoots (LFS) to adjacent non-labeled shoots (NLFS), both located within 10 cm on the same main scaffold of V-shaped peach trees. At Stages I and III of fruit growth, fruit and shoot tips were sampled from LFS and NLFS to determine (13)C percentage on the day of labeling and after one week. Factors that differed among the three experiments in the two years were cultivar, tree age, source:sink ratios and labeling time. In all cases but one, no (13)C was found in fruits or shoot tips of NLFS. Only at Stage III of 'Redhaven' peach fruit growth (2005) was (13)C detected in fruits of NLFS, but only in the treatment favoring movement, and on the day of labeling. When L:F was altered to the maximum extent possible and branches were girdled at their base (complete sink removal, 2006), a detectable concentration of (13)C was recovered in fruits of NLFS at both growth stages, indicating that (13)C movement across adjacent shoots is possible, and detectable by (13)C tracing. According to our results, peach branches are relatively autonomous even at the fruiting-shoot level. However, conditions of strong imbalance between source supply and sink demand, either experimentally imposed or during periods of strong sink competition, may cause some movement of carbon among neighboring shoots.
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