Consideraciones Prácticas

3.2.1 Experimental design

In a commercial orchard located in Te Puna, Bay of Plenty, an experiment was established in the form of a 2 × 2 matrix of treatments, consisting of 56 ‘Hayward’ kiwifruit female vines with manipulated crop load (industrial average, 36 t/ha and ultrahigh, 43 t/ha) and the application (or not) of girdling. There were 16 vines each for low crop load treatment with and without girdling, and 12 vines each for high crop load treatment with and without girdling. The vines were about 35 years old and grown on a pergola using opposing females. Hydrogen cyanamide was used at commercial rates to treat the vines to improve budbreak and reduce the incidence of side flowers.

Crop thinning occurred on 4 – 5 January 2013 (42 – 43 day after full bloom; DAFB) and trunk girdling occurred on 10 December 2012 (17 DAFB) and 2 February 2013 (71 DAFB). The fruit thinning in this experiment was designed to simulate conventional fruit thinning practices, in which the smallest fruit and poorly shaped or

‘Hayward’ marked (a shallow sunken line running down the side of the fruit, sometimes

ending in a hook or protuberance caused by a stamen sticking to the fruit and the hook by an anther sticking) were removed first, and the remaining fruit removed to reach the final crop load by taking into consideration the local leaf to fruit loading relative to shoot length. Prior to pollination the vines were flower-thinned to remove any side flowers. Fruit were then thinned to the final crop load 6 weeks after the last pollination.

Selected vines for each treatment were arranged according to a four-by-four Latin square (Fig. 3.1) with each treatment represented on each row and column of the trial as plots, which accounted for in-orchard location effects but avoided unusual plants caused by e.g. regrafting. Commercial harvest occurred on 15 May 2013, with all treatments being harvested on the same day. At harvest, 24 trays of 30 mixed-sized fruit per tray were sampled from each of the four plots for each treatment representing replicates. The samples were collected by dividing each vine quarter into 9 quadrants and then randomly sampling a fruit from each quadrant. Fruit were delivered from the orchards in Te Puke and cured at ambient temperature for two days during transport. Fruit trays arrived at Massey University on 17 May 2013, and were wrapped in polyliner films and stored at 20 °C overnight before the commencement of measurements (day 0).

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HCG LC HC LCG

LCG HC LC HCG

LC LCG HCG HC

HC HCG LCG LC

3.2.2 Fruit quality attributes

The at-harvest (prior to transportation) fruit weight, DMC and TSS of kiwifruit were randomly collected from 90 fruit of each treatment at the packhouse. The TSS and FF were also monitored upon arrival at the laboratory (day 0) and during storage (14 – 175 days). Single trays (30 fruit) from each of the 16 plots were assessed destructively for FF and TSS at 0, 14, 28 and 50 days. Four trays (120 fruit) from each of the 16 plots were measured at 25-day intervals from 75 to 175 days. During storage, ethylene concentration in the cool room was monitored using ethylene analysing equipment (photoacoustic ETD-300, Sense B.V., Nijmegen) and maintained below 5 nL L-1_{. Fruit} were equilibrated to ambient temperature (20 ºC) over a period of 15 hours prior to fruit quality measurement.

Fruit weight (g) was measured by using a digital balance (Mettler PG-503S, Toledo, Switzerland) with 0.001 g accuracy. The DMC (%) was determined using an oven drying technique by dehydrating a known mass of 2-3 mm thick equatorial fruit slice at 60-65°C for 24 hours. Data were expressed as percentage of the wet mass. The FF (N) was measured using an electronic QALink Penetrometer (Willowbank Electronics Ltd., Napier, New Zealand) fitted with the standard 7.9 mm Magness-Taylor probe. Two measurements of peak penetrating force were made at two locations (90° apart) around the equator of the fruit after removal of a thin layer (1 mm) of the fruit skin. The penetration speed was 20 mm s-1 _{and the puncture depth was 8 mm. The TSS}

Figure 3.1 Design of orchard layout to minimise in-orchard location effects. HCG: High crop load with girdling. LCG: Low crop load with girdling. HC: High crop load. LC: Low crop load. Letters represent different rows whereas numbers represent different columns. Each square represents a single plot.

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(ºBrix) was measured using a digital pocket refractometer (PAL-1, Atago, Japan) using the juice taken from both end caps of the fruit. The proportion of soft fruit during

storage was calculated as the percentage of fruit with FF values below 9.8 N.

3.2.3 Data analysis

The effects of preharvest factors on fruit quality both at harvest (before transportation), at day 0 (after arrival at laboratory) and during storage were investigated. In addition to the measured quality attributes, fruit dry weight (DW), which is a combination of solid materials (excluding water) within the fruit, was calculated as fresh weight × DMC. The ratio of at-harvest TSS to DMC (TSS/DMC) indicates the proportion of solubilised sugar relative to total carbohydrate storage, and hence can be used as an alternative measure to represent maturity at harvest. This was also calculated for this study.

Data analysis for comparison of factors and calculation of least significant differences (LSD) was carried out at the plot level using the general linear model (GLM) in Minitab® _{(Version 16.1.0, Minitab Inc., Pennsylvania, USA). Factors considered} included crop load, trunk girdling and the interaction between the two. In addition, comparisons of incidence of soft fruit (FF < 9.8 N) amongst treatments were carried out using a Chi-square test in Minitab®_.