Typical canopy architecture of a kiwifruit vine can generate a large degree of self-shading, as the uppermost leaves intercept the vast majority of photosynthetically active radiation (PAR) and shade the lower layers of the canopy. Reflective cloth is a tool that can be used to reflect the light that passes through large gaps between plants, falls onto the ground and back up onto shaded leaves. The current study assessed the effects of two different reflective cloth installations (Full: reflective cloth covering the majority of the inter-row sward, and Strip: 1-m wide strips of reflective cloth laid on the sward underneath the gap between male and female canopies) on fruit quality and on light distribution around the vine. Trials were performed in two commercial Actinidia chinensis var. chinensis 'Zesy002' kiwifruit orchards (Orchard X and Orchard Y). At Orchard Y, both Full and Strip treatments increased (albeit not significantly) the proportional changes in fruit fresh weight m(-2) and dry weight m(-2) by 12-17% and 5-10%, respectively, compared with the control (i.e., grass). However, no effects of treatment on fruit quality were observed at Orchard X, despite both treatments increasing light dispersal under the canopy, compared with the control. We suggest that the difference in fruit quality between orchards was because reflective cloth at Orchard Y reflected approximately double the amount of light reflected at Orchard X. Less light was reflected at Orchard X because the strung-cane system reduced the amount of incident light falling onto the ground. This study highlights the value of small increases in light distribution in a plant canopy, and indicates the potential for further improvements in kiwifruit quality if canopy management is optimised.

Previous studies have shown that photosynthates are translocated considerable distances in kiwifruit vines. However, it has also been demonstrated that fruit in densely shaded areas of the canopy can be of inferior quality to fruit from more open canopy areas. This suggests that in areas of dense shade, fruit are unable to import sufficient carbohydrates to compensate for local scarcity. This trial involved Actinidia chinensis var. chinensis 'Zesy002' vines on an orchard where dense shading within the canopy had resulted in significant leaf drop on some lower-vigour shoots by late summer. Two types of shoots were selected in early autumn: shoots with minimal leaf drop ("healthy"), and shoots that had lost all leaves ("leafless"). Five shoots of each type were evaluated from 22 vines. Fruit quality of the terminal fruit from labelled shoots was assessed at commercial harvest (mid-April). Fruit number shoot(-1), and diameters of the pedicel, shoot base and parent cane internode were also recorded. Fruit quality was significantly worse on leafless shoots, with fruit 14 g lighter, 1.5 percentage units lower in dry matter content and having delayed maturity. The low quality fruit from leafless shoots could be selectively removed prior to harvest to reduce variability in the fruit pool. The reduced photosynthate import into fruit is likely a result of vascular shutdown, but the causal mechanism remains unclear. Future research could provide a clearer understanding of mechanisms that trigger leaf senescence and vascular shutdown, and how these can be mitigated.

Girdling, otherwise known as cincturing or ring barking, was tested for its ability to improve yield and quality of Actinidia chinensis var. deliciosa ‘Hayward’, A. chinensis var. chinensis ‘Hort16A’ and, more recently, A. chinensis var. chinensis ‘Zesy002’ kiwifruit grown commercially in New Zealand. Originally, we developed girdling of individual 1-year-old fruiting canes as a technique to increase fruit size for organic kiwifruit growers. However, the technique was rapidly adopted by growers of conventional kiwifruit. Girdles healed rapidly within 3-6 weeks of application, and plants recovered fully. Cane girdling was largely superseded by girdling of the main trunks, which resulted in similar benefits to cane girdling, but was faster to apply, responses were larger, and there was less variability of fruit characteristics within vines. However, there was some risk of negative plant responses if girdles were applied too deeply, so that the xylem tissue was damaged, or when girdles were applied late in the growing season. In both of these cases, girdles did not always heal before winter, and development of leaf canopies in spring was retarded. Timing of girdle applications was critical for response. Girdles applied soon after fruit set, during the rapid phase of fruit growth, increased fruit weight, while those applied during the starch accumulation phase increased dry-matter content of fruit and improved the eating quality of fruit. Girdles applied in autumn increased bud break and flower numbers of vines in the following season. The story of how girdling was developed for New Zealand kiwifruit growers is also an informative case study. It demonstrates that a significant extension plan is required for the rapid adoption of even a relatively simple new technology by a horticultural industry.

Systemic movement of Pseudomonas syringae pv actinidiae (Psa) was investigated in inoculated potted kiwifruit vines in a greenhouse and in naturally infected mature vines in the orchard In the potted vine experiment trunks of 2yearold Actinidia chinensis Hort16A on the rootstock A deliciosa Bruno were woundinoculated with Psa After 151 days Psa was detected up to 95 cm from the point of inoculation Psa moved upwards and downwards within the trunks and through the scion and the rootstock at similar rates In the orchard experiments samples were taken from mature kiwifruit vines at intervals along the vines during autumn winter and spring Psa moved systemically throughout mature Hort16A and A deliciosa Hayward kiwifruit vines and was detected in symptomless tissues In both greenhouse and field situations Psa was not inhibited by the graft union and was able to move into the rootstock and down to the base of the vine

Actinidia chinensis 'Hort16A' kiwifruit vines are considerably more vigorous than A. deliciosa 'Hayward' vines. Growers have considerable difficulty managing canopies to prevent heavy internal shading and an abundance of tangled shoots developing in summer. In recent years, management of 'Hort16A' kiwifruit vines has focused on techniques to counter the strong vegetative growth in spring and early summer. Pruning gels that contain naphthalene acetic acid (NAA) reduce this growth substantially. NAA gels applied to cut shoots also stimulate very substantial increases in fruit weight. Whilst NAA gels may be valuable vine management tools for kiwifruit, we have demonstrated that a reliance on them can compromise fruit quality by reducing fruit dry matter content (% DMC) and delaying the development of yellow flesh colour. Reduced and more targeted use of NAA gels is a better approach to maximise both fruit quality and orchard profitability.

In New Zealand, continued improvements in 'Hayward' kiwifruit orchard management have increased yields more than four-fold since 1975. Top performing orchards now produce 10,000 Class 1 trays/ha (36 t/ha), with some blocks producing 15,000 trays/ha (54 t/ha). We wanted to know how much further we could increase yields from this cultivar. Projects to examine this were established in 2006 using vines planted with 5.8x4.6 m spacing, providing 27 m(2) of productive canopy area per vine. Vines were trained on pergola support structures with opposing female canopies (OFM); male vines were trained across female rows. During the period 2002-2006 inclusive, these vines had produced 13-15,000 trays/ha/per year. The target was to increase this to 20,000 trays per ha (72 t/ha), with the additional fruit carried on new secondary canopies trained as vertical curtains below the pergola fruiting canopies. Additional management practices included use of reflective ground covers, artificial pollination and trunk girdling. During the trial period, half the block was converted to strip males (SM); male vines were trained along alternate rows, replacing existing female vines in that row, to provide an additional 19 m(2) of usable productive area per female vine canopy (46 m(2) in total). Use of secondary canopies on OFM vines increased fruit yields by 3,295 trays/ha to 20,415 trays/ha (73.5 t/ha). Fruit weight (FW) and dry matter concentration (DM) decreased significantly with increasing fruit numbers per vine and vines had significant leaf yellowing and several dead leaves at commercial harvest, suggesting these vines growing on this OFM system were close to their limit in terms of economic productivity. In contrast, SM vines carrying almost twice as many fruit per plant as OFM vines, but with similar fruiting densities (fruit/m(2)), showed only weak relationships between high fruit number and reduced FW or DM, and the leaf canopies were still in excellent condition at commercial harvest. These results suggest that these vines growing on this SM system were not at their limit of productivity and that further increases in economic yields are possible with changes to training systems and canopy architecture.

Fruit dry matter content (DM) of kiwifruit, defined as the fruit dry weight (DW) expressed as a percentage of the fresh weight (FW), is used as an indicator of eating quality. A high DM at harvest results in increased consumer satisfaction. To determine the role of carbohydrate availability and sink competition in altering fruit size and DM at commercial harvest, we used an experimental model system based on phloem-girdled shoots to manipulate the number of source leaves, fruit and vegetative sinks on a shoot of 'Hayward' kiwifruit. Commercially produced kiwifruit fruits typically weigh 95-115 g and have a DM of 14-17 units (this is a percentage but the % sign has not been shown, to reduce confusion with changes in DM expressed as a % change). With our experimental system, this corresponded to the fruit growth observed with two to three leaves when there was no vegetative competition. With four source leaves and a single fruit, competition from a vegetative regrowth reduced fruit fresh weight by 28% and dry weight by 39%. With two fruit, and no vegetative sink, between-fruit competition had less severe effects on the fruit and dry weight. Doubling the number of fruit on a girdled shoot reduced average fruit fresh weight by 15%, dry weight by 23% and DM by 12%. With a high source supply (seven leaves with no regrowth competition) fruit growth was very high with a fresh weight of 174 g and 18.4 DM, substantially above that of commercial production.

Gold kiwifruit (Actinidia chinensis Planch. var. chinensis 'Hort16A') is an important crop for New Zealand. In this trial, all nutrients, except nitrogen (N), were applied at levels comparable to commercial practice. The control treatment received approximately 145 kg N/ha/y, a conservative rate of N application for kiwifruit. The zero-N treatment vines received all nutrients except N, and the high-N treatment received double the control levels of N. Carbohydrate concentrations in the leaves, fruit and canes of zero-N and high-N vines were determined periodically through the season for two years. There were lower total sugar concentrations in the leaves of the zero-N vines however total carbohydrate concentration content was higher in the zero-N fruit. Vegetative vigor was reduced in the zero-N vines when compared to the high-N vines. By reducing N, the partitioning of carbon to fruit appears favored. This effect may be due to modified sink strength under reduced N.

ABSTRACT Gold kiwifruit (Actinidia chinensis Planch. var. chinensis ‘HORT16A’, marketed as ZESPRI™' ‘HORT16A’) is an important export crop for New Zealand. Nutrient management, including the application of nitrogen (N), for ‘HORT16A’ kiwifruit has mimicked strategies for the green (A. deliciosa ‘Hayward’) cultivar, however, physiological differences between Actinidia species necessitate the development of specific nutrient regimes for ‘HORT16A’ vines. In this trial, all nutrients, except N, were applied at levels comparable to commercial practice. The Control treatment received approximately 145 kg N ha/y, and was based on estimates of total N removed each year in the harvested fruit. The Zero-N treatment vines received all nutrients except N, and the High-N treatment received double the Control, approximately 295 kg N ha/y, for two consecutive seasons. The High-N treatment represents the upper limit of N application practices in commercial ‘HORT16A’ kiwifruit production. Zero-N fruit had higher calcium (Ca) and lower N concentration than High-N fruit in both seasons. Fruit potassium (K) and magnesium (Mg) concentrations were equivalent between these treatments in both seasons. Fruit phosphorus (P) concentration throughout the season was increased in the High-N treatment in both years. Fruit sizes were not different between treatments at final harvest in Year 1, being 130.5 ± 4.13 g, 125 ± 1.49 g, and 125 ± 3.29 g for the High, Control, and Zero-N vines, respectively. Larger fruit were harvested from the High-N vines (125 ± 4.69 g) in Year 2, than from either Control (113 ± 2.03 g) or Zero-N (118 ± 1.03 g) vines. Percent fruit dry matter (DM) content was higher in the Zero-N fruit (17.2 ± 0.06, 17.2 ± 0.06, and 16.8 ± 0.14 for Zero, Control, and High-N vines) at final harvest in Year 1. But values of fruit DM for all treatments were similar in Year 2 in spite of fruit size differences between treatments. Fruit DM for all treatments was slightly higher in Year 2 than in Year 1. Differences in fruit mineral concentration and fruit maturity at harvest may have contributed to increased incidence of low temperature breakdown (LTB) in the High-N fruit in Year 1. In Year 2, when fruit DM was higher in all treatments, yellow coloration was more developed. Total fruit N concentration was lower in Year 2 for all treatments than in Year 1, and LTB was minimal and not different between treatments. Leaves from Zero-N vines had reduced N in both years compared with Control and High-N vines. In contrast, leaf Ca and Mg concentrations were reduced in High N-vines, compared with values recorded in Zero-N vines in both seasons. Leaf K concentrations were comparable between treatments in both seasons. Leaf sulfur (S) concentration was reduced under the High-N treatment, and leaf P levels were increased under the High-N treatment in both years. These data demonstrate that N application influences the uptake and accumulation of other mineral elements in ‘HORT16A’ kiwifruit. In order to encourage desirable nutrient concentrations in both the fruit and leaves of ‘HORT16A’ kiwifruit, a reduction in N applied is suggested, and this would have little or no detrimental effect on vine performance over two seasons. Reduced N application will also reduce nitrate leaching which is estimated at 39 kg N ha/y under the Control treatment.

Because of its short production history, limited knowledge exists of the water and nitrogen requirements for 'Hort16A' (ZESPRI(TM) GOLD). Our research aims to address this knowledge gap using a measurement and modelling approach. A three-year field trial has been established on a mature orchard near Te Puke, New Zealand. Two fertiliser regimes (120 and 250 kg N ha(-1)) have been set up to apply nitrogen fertiliser (calcium ammonium nitrate) as a single dressing in the spring time, and a third treatment receives zero fertiliser. Whole shoots are destructively sampled every month to determine the dry-matter allocation and nitrogen content of shoots, leaves and fruit of the new season's growth. Soil water content is measured using time domain reflectometry (TDR). Soil samples to 2.4 m depth are taken every month to follow changes in the mineral nitrogen content (i.e., nitrate and ammonium) of the root-zone soil. These data are providing parameters for a computer model (SPASMO - Soil Plant Atmosphere System Model) of the water, carbon and nitrogen budget of the orchard.Results from the first year of the trial suggest that 90-110 kg ha(-1) of nitrogen is accumulated in the fruit. Some 60-80 kg ha(-1) of nitrogen is accumulated in shoots and leaves of the current season's growth, although this is largely returned to the soil as leaf litter and winter prunings. Preliminary findings suggest the high nitrogen treatment (250 kg N ha(-1)) may delay fruit maturity and reduce fruit quality plus encourage excessive nitrate leaching. Measurements in coming seasons will investigate the physiological cost to the vine of the zero fertiliser treatment. The ultimate goal of this research is to develop new modelling tools that will help to optimise the amount and timing of fertiliser to achieve maximum vine performance with minimum environmental impact.

Root pressure was measured continuously over spring in eight clonal kiwifruit rootstocks selected from seven Actinidia species (A. chrysantha, A. deliciosa, A. eriantha, A. hemsleyana, A. kolomikta, A. macrosperma, A. polygama), using pressure transducers and miniature compression fittings. Rootstocks that promoted scion vigour developed root pressures up to 0.15 MPa before or during scion budburst, whereas those that reduced scion vigour developed root pressure up to 0.05 MPa only after scion shoot expansion. When several seasons were compared, the date of onset of root pressure and the magnitude of pressure achieved were consistent for each rootstock. Root pressure was first recorded between late July and early September in vigour-promoting rootstocks, while scion budburst and initial shoot growth were in late August and early September. Vigour-reducing rootstocks did not develop significant root pressure until October. The date of onset was similar for the grafted rootstock and ungrafted plant of the same clone, but was not clearly related to the timing of shoot growth by the ungrafted plant. In the grafted plants the leaf and xylem water potentials of the scion were more negative, midday turgor was 0.3-0.5 MPa lower, and wilting was sometimes observed in developing shoots growing on low-vigour rootstocks, indicating that water stress was contributing to reductions in growth. Leaf turgor was correlated with average root pressure but not pressure measured during the day, suggesting that root pressure was not supporting transpiration during peak flows and was, instead, indicative of higher root hydraulic conductance. The rapid temporal rise in root pressure observed each spring in the various rootstocks was not accompanied by changes in xylem sap solute potential, but when rootstock clones were compared those that developed higher root pressures had higher sap solute potentials. Xylem sap solute potential varied between rootstocks from -0.07 MPa to -0.15 MPa, while root pressures measured at the same time varied between 0.0 MPa and 0.09 MPa, suggesting that an osmotic mechanism could account for the observed root pressure. Differences in phenology between the rootstocks and scion appeared to account for the rootstock effects on shoot growth, and changes in root pressure provided a useful indication of seasonal changes in root hydraulic properties and solute transport behaviour.

Patterns of shoot development and the production of different types of shoots were compared with scion leaf area index (LAI) to identify how eight clonal Actinidia rootstocks influence scion development. Rootstocks selected from seven Actinidia species (A. chrysantha Merri., A. deliciosa (A. Chev.) C. F. Liang et A.R. Ferguson, A. eriantha Benth., A. hemsleyana Dunn, A. kolomikta (Maxim. et Rupr.) Maxim., A. kolomikta C.F. Liang and A. polygama (Sieb. et Zucc.) Maxim.) were grafted with the scion Actinidia chinensis Planch. var. chinensis 'Hort16A' (yellow kiwifruit). Based on an earlier architectural analysis of A. chinensis, axillary shoot types produced by the scion were classified as short, medium or long. Short and medium shoots produced a restricted number of preformed leaves before the shoot apex ceased growth and aborted, resulting in a 'terminated' shoot. The apex of long shoots continued growth and produced more nodes throughout the growing seasons. Mid-season LAI of the scion was related to the proportion of shoots that ceased growth early in the season. Scions on low-vigor rootstocks had 50% or less leaf area than scions on the most vigorous rootstocks and had a higher proportion of short and medium shoots. On low-vigor rootstocks, a higher proportion of short shoots was retained during pruning to form the parent structure of the following year. Short parent shoots produced a higher proportion of short daughter shoots than long parent shoots, thus reinforcing the effect of the low-vigor rootstocks. However, overall effects of rootstock on shoot development were consistent regardless of parent shoot type and nodal position within the parent shoot. Slower-growing shoots were more likely to terminate and scions on low-vigor rootstocks produced a higher proportion of slow-growing shoots. Shoot termination also occurred earlier on low-vigor rootstocks. The slower growth of terminating shoots was detectable from about 20 days after bud burst. Removal of a proportion of shoots at the end of bud burst increased the growth rate and decreased the frequency of termination of the remaining shoots on all rootstocks, indicating that the fate of a shoot was linked to competitive interactions among shoots during initial growth immediately after bud burst. Rootstock influenced the process of shoot termination independently of its effect on final leaf size. Scions on low-vigor rootstocks had a higher proportion of short shoots and short shoots on all rootstocks had smaller final leaf sizes at equivalent nodes than medium or long shoots. Only later in the development of long shoots was final leaf size directly related to rootstock, with smaller leaves on low-vigor rootstocks. Thus, the most important effect of these Actinidia rootstocks on scion development occurred during the initial period of shoot growth immediately after bud burst.

Cuvettes that heat individual fruits on a kiwifruit vine were used to determine how the characteristics of Actinidia chinensis 'Hort16A` fruit are affected by temperature at various stages of fruit development. Each cuvette fitted around a single kiwifruit and a radiant heating element heated the enclosed fruit. Cuvette temperatures were controlled so that each fruit was kept about 4 degrees C warmer than ambient fruit. Heating individual fruit during the early, mid and late periods of the growing season was found to have some immediate effects, and also effects that persisted until harvest. There was an immediate effect on fruit growth, which was most marked early in the season, and which resulted in larger fruit at harvest. Also, heating fruit early in the season increased the soluble solids content at harvest, as well as inducing more yellow (lower hue angle) and softer fruit at harvest. Heating fruit just prior to harvest increased their final dry matter concentration.

The responses of fruit and shoot growth of 'Hayward' kiwifruit vines to changes of temperature were determined during spring, summer or autumn. Mature vines were warmed 2-5°C above ambient temperatures by enclosing them in temperature-controlled tunnel houses for 34-89 d. Increasing temperature during spring advanced the date of flowering by 17 d and increased the rate of shoot elongation by 6 mm d-1 °C-1. The fruit on these early-flowering vines were larger and had a higher dry matter concentration than control fruit during the first part of the season. Increasing temperature during summer increased the rate of shoot elongation but reduced fruit growth, accumulation of dry matter in fruit and fruit firmness. In contrast, increasing temperature during late autumn increased fruit growth but reduced the soluble solids concentration (SSC) of fruit and thus, delayed commercial maturity. When fruit growth data for summer and autumn were combined the variation in fruit growth with temperature could be described by a single quadratic curve. Maximum fruit growth occurred at 17°C and temperatures above or below this optimum reduced fruit growth. Consequently, during summer when ambient temperatures averaged 17°C, warming vines decreased fruit growth, while during late autumn, when ambient temperatures had fallen to 13°C, warming vines increased fruit growth. Warming vines during summer reduced both the SSC of ripe fruit and the vitamin C concentration. Warming vines during autumn increased SSC but reduced the vitamin C concentration.

Whole-plant hydraulic conductance, shoot growth, and leaf photosynthetic properties were measured on kiwifruit vines with four clonal rootstocks to examine the relationship between plant hydraulic conductance and leaf stomatal conductance (gs) and to test the hypothesis that reduced hydraulic conductance can provide an explanation for reductions in plant vigour caused by rootstocks. The rootstocks were selected from four species of Actinidia and grafted with Actinidia chinensis var. chinensis 'Hort16A' (yellow kiwifruit) as the scion. Total leaf area of the scion on the least vigorous Actinidia rootstock, A. kolomikta, was 25% of the most vigorous, A. hemsleyana. Based on shoot growth and leaf area, the selections of A. kolomikta and A. polygama are low-vigour rootstocks, and A. macrosperma and A. hemsleyana are high-vigour rootstocks for A. chinensis. Whole-plant hydraulic conductance, the ratio of xylem sap flux to xylem water potential, was lower in the low-vigour rootstocks, reflecting their smaller size. However, leaf-area-specific conductance (Kl) and gs were both higher in the low-vigour rootstocks, the opposite of the expected pattern. Differences in Kl were found in the compartment from the roots to the scion stem, with no difference between rootstocks in the conductance of stems or leaves of the scion. There was no evidence that the graft union caused a significant reduction in hydraulic conductance of vines with low-vigour rootstocks. Leaf photosynthetic capacity did not vary between rootstocks, but photosynthesis and carbon isotope discrimination (Delta13C) under ambient conditions were higher in the low-vigour rootstocks because gs was higher. gs and Delta13C were positively correlated with Kl, although the mechanism for this relationship was not based on stomatal regulation of a similar xylem water potential because water potential varied between rootstocks. For Actinidia rootstocks, changes in Kl do not provide a direct explanation for changes in vigour of the scion. However, depending on the rootstock in question, changes in hydraulic conductance, biomass partitioning, and crown structure are involved in the response.