3.2 . 1 Girdling of fruiting lateral shoots
The individual fruiting lateral shoots to be girdled were selected arising from a number of one year old canes on T-bar trained kiwifruit vines at the Massey University Fruit crops unit (MUFCU) . Kiwifruit fruiting characteristics are affected by the type of lateral shoot (Lai et aI., 1 990), and by how well the lateral shoot is exposed to incoming radiation (Grant and Ryugo, 1 984). Thus to eliminate these variables, the lateral shoots were always selected with uniformity in mind and strongly growing, indeterminate and well exposed lateral shoots were used. Thin lateral shoots were never used as these have low physical strength after girdling .
. •• f---- L eaf: fruit ratio=l
• f---- Leaf:fruit ratio=4
Figure 3. 1 Diagrammatic representation of a girdle applied to kiwifruit lateral shoots with a leaf:fruit ratio of either one or four.
Girdling was performed by making two parallel cuts around the entire circumference of the base of the shoot with a double bladed knife, ensuring that the cut was made to the depth of bark and not into the wood. The bark was then peeled away and the girdle was
3-4 3 : Lateral Shoot of Kiwifruit. Materials and Methods
checked to ensure the complete absence of vascular connection. Girdles were 1 0 mrn wide. Fruit numbers were reduced to two fruit per shoot and leaves were then thinned to give the required leaf:fruit ratio on the shoot, retaining only fully expanded, well exposed leaves. A leaf:fruit ratio of four consisted of eight leaves and two fruit, while a ratio of one consisted of two leaves and two fruit (Figure 3. 1 ). Shoots were checked monthly between January and April for re-growth from axillary buds which was subsequently removed so that the source-sink ratio was not altered.
3.2.2 The effect of leaf:fruit ratio and time of girdling on fruit weight and percentage dry matter
Season one
Experimental design was a randornised complete block design with a factorial treatment structure. Seven levels of girdling date: 0, 7, 1 4, 28, 42, 56 days after full bloom (DAFB) and control (not girdled) were applied in combination with two levels of leaf:fruit ratio on a lateral shoot (one and four). Each treatment combination was replicated on two lateral shoots on each of six vines. Shoots were allocated randomly to treatment combinations by tagging at full bloom, and at this time all shoots were pruned to the appropriate leaf:fruit ratio. At the time of girdle application, a 1 0 mrn girdle was applied
near the base of the shoot as described in section 3.2. 1 .
Fruit were harvested at 1 60 DAFB, at which point other fruit sampled randomly in the same block were at commercial maturity (soluble solids=6.2%). Measurements were taken of fruit fresh weight, soluble solids and surface seed numbers (chapter two). Fruit dry weight was established by drying the entire sliced fruit to a constant weight in a ventilated oven at 70°C.
Season two
In order to confirm a trend in the data, the high leaf:fruit ratio treatments were repeated in the following season with the additional girdling times of 2 1 and 70 DAFB.
3 : Lateral Shoot of Kiwifruit. Materials and Methods
3.2.3 The effect of leaf:fruit ratio on cell division and expansion in kiwifruit
3-5
At seven DAFB, well exposed indetenninate fruiting lateral shoots were selected on two adjacent vines. Coloured tags signifying treatments were randomly placed on these lateral shoots, and leaffruit ratio was adjusted to either one or four. An effort was made at this time to ensure that fruitlets were even in size, and not misshapen. Girdles were placed at the base of each lateral shoot at seven, 28 or 56 DAFB as described in section 3.2. 1 . One girdled shoot per vine was harvested from any one treatment at selected intervals throughout the season. Fruit fresh weight was measured, and a transverse slice was taken from the point of minimum equatorial diameter. Pennanent transverse sections were made, and cell counts were perfonned across the core in the direction of the minimum and maximum equatorial diameter (Dmin and Dmax respectively), and in inner pericarp and outer peri carp in the direction of Dmin as described in chapter two.
3-6 3 : Lateral Shoot of Kiwifruit. Results
3.3 Results
3.3.1
Fruit weight and dry matter accumulationIn season one, the leaf:fruit ratio within the shoot had no effect on any parameter unless a girdle was applied (Table 3. 1 ). There were significant interactions between the time at which girdles were applied and the leaf:fruit ratio for all the fruit parameters measured except seed numbers (soluble solids P=0.026, percentage dry matter P=0.0025, fresh and dry weight p<0.0001 ). There were no significant main effects of treatment or date on fruit seed number. Soluble solids was strongly correlated to the percentage dry matter (Figure 3.3), and for this reason further discussion is confined to the percentage dry matter.
Table 3. 1 The seed number, soluble solids, fresh weight, dry weight and percentage dry matter of fruit on shoots which were not girdled (control) at two leaf:fruit ratios in season one. Due to the presence of missing values, means shown are population marginal means I of up to 1 2 shoots per treatment.
Leaf:fruit ratio
one four
Fresh weight (g) 96 (34) 97 (34)
Dry weight (g) 1 2.9 (0.6) 1 2.9 (0.6)
% dry matter 1 3 .4 (0.2) 1 3 . 1 (0.2) Soluble solids (OBrix) 7.6 (0.4) 6.4 (0.4)
Seed number per fruit 945 (78) 9 1 7 (78)
1 For description of population marginal means, see chapter two, section 2.8.3. Standard error of mean in parentheses.
Low leaf:fruit ratio one season one
Contrast (P>F) (one vs. four) 0.8 1 03 0.9857 0.2694 0.0794 0.8337
At a low leaf:fruit ratio, fresh weight, dry weight, and the percentage dry matter of fruit from girdled shoots was significantly lower (contrast, P<0.05) than controls at all
3 : Lateral Shoot Girdling of Kiwifruit. Results 3-7 girdling dates (Figure 3 .2). However, between the different dates when shoots were girdled, there was no evidence of any significant differences for any parameter, even between shoots which had been girdled as far apart as 56 days. Fresh weight averaged 6 1.9g across all girdling dates, while dry weight averaged 6.5g. Across all of the girdling dates, the percentage dry matter was reduced from 1 3 .4% in control fruit, to 1 0.8% in fruit from girdled shoots (Table 3.2).
The mean fresh weight of fruit from all girdled shoots at the high leaf:fruit ratio was higher than from control shoots. However only fruit from shoots girdled at full bloom (FB) or 28 DAFB were significantly heavier than control fruit (contrast, P=O.O 1 57 , 0.0460 respectively). Fruit from shoots girdled at 1 4 DAFB had a significantly lower dry weight (contrast, P=0.0083 , 0.0255 respectively) than fruit from shoots which were girdled at FB or 28 DAFB (Figure 3 .2), and were in fact not significantly different to fruit from non-girdled control shoots (contrast, P=0.2776). Furthermore, these fruit had a significantly lower percentage dry matter, than fruit from control shoots (contrast, P=0.003). In contrast, when fruit from 1 4 DAFB were excluded from the analysis, there was no evidence that the percentage dry matter of fruit from girdled shoots with a high leaf:fruit ratio were significantly different from control fruit (Table 3 .2). Percentage soluble solids CBrix) followed a very similar pattern to the percentage dry matter (Figure 3 .2), and there was a strong l inear relationship between these two variables (Figure 3.3).
HighJyjltfmit
In order to check the comparatively low fruit weight and dry matter content of fruit from shoots with a high leaf:fruit ratio girdled at 1 4 DAFB was real, this part of the experiment was repeated.
A similar trend to that found in the previous year was detected, although it was not as marked (Figure 3 .4). The fresh and dry weight, and percentage dry matter of fruit on shoots girdled at 14 DAFB were lower than from shoots girdled at 7 or 2 1 DAFB, although differences were not statistically significant.
3-8 Chapter 3: Lateral Shoot of Kiwifruit. Results