Reduction in AFL data collection

In the first season, during AFL monitoring fruit losses assessments were made on 9 measurement occasions (at 3 d intervals over 27 d). A substantial number of rotten fruit were recorded after 21 d and firmness loss was difficult to assess. Therefore, in later seasons the number of measurement occasions were reduced to 7 (at 3 d intervals over 21 d) to minimise the fruit waste at later stages of AFL monitoring. A usual kiwifruit softening pattern expresses three phases, an initial slow phase, a secondary rapid phase and final slow phase (Benge et al., 2000). Enough data points are required to be collected to exhibit all phases of softening to enable later CG model fitting. Firmness data in later seasons showed that 8 data points (from 0 - 21 d at 3 d intervals) were enough to express the three softening phases with the exception of 6 GLs (in both seasons) which had an extended initial lag phase (18 - 21 d, Figure 5.4 and Figure 6.3). A reduction in the number of data points required to describe that complete softening curve can be advantageous to minimise the effort and cost required for AFL application. The initial slow and secondary rapid phases differentiate GL softening patterns.

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However, differences between GLs decrease, as fruit become very soft (below 1 kgf, Figure 5.4 and Figure 6.3). Hence, to characterise the softening change at 20 °C, storage duration could perhaps be reduced to 18 or 15 d instead of 21 d. Alternatively, the time interval between measurement occasions could be extended (e.g. to 6 d instead of 3 d) to reduce the number of data points describing the GL softening patterns. Fortunately, we are able to process existing data sets to determine the impact of these potential modifications.

AFL softening data of 57 GLs collected in 2011 (Section 4.2) was used to compare different data collection patterns post-hoc (after the fact). From the data set collected over 21 d at 3 d intervals, data points at 21 and 18 d were obscured to follow the influence of using AFL storage durations of 18 and 15 d respectively. Alternatively, to analyse the effect of collecting data at extended intervals, data points collected at 6 d intervals were used (i.e. 0, 6, 12 and 18 d). The CG equation was again fitted with non- linear mixed effects to the modified AFL softening data (Section 5.2.1.2 and Section 5.2.1.3). Global ($R and E) and GL dependent (% and N) parameters were extracted for

each modified data collection pattern and compared. Rate of firmness change (N) of curves for different data collection patterns were also assessed for correlation with SF at 100 and 126 d of optimal storage.

Fitted values of %for softening curves in all four data collection patterns (21, 18, 15 d with 3 d interval and 18 d with 6 d interval) did not substantially vary (P > 0.05, Table 7.1 Appendix 5). Rate of firmness change (N) of curves representing data for 18 and 15 d were statistically different from 21 d (P < 0.05, Table 7.1). Both average and range of N decreased as the storage duration was reduced. The highest N value decreased more than the lowest value with the reduction in storage duration, meaning that for most rapidly softening GLs, the fitted N was most influenced. Overall, GL dependent parameters (% and N) for curves representing duration of 18 and 15 d were highly correlated (r = 0.99) with the fitted values for softening data collected in 21 d with 3 d interval (Appendix 5).

121 Table 7.1: Comparison of GL dependent parameters of CG fitted to softening data

representing different data collection patterns.

Data collection pattern (day)

GL dependent

% N

Means Range Means Range 21 5.03A 2.65 to 6.93 0.67A 0.23 to 0.94 18 5.23A 2.93 to 6.94 0.49C 0.12 to 0.74 15 5.40A 3.20 to 7.16 0.43D 0.12 to 0.61 18 (with 6 day intervals) 5.32A 2.90 to 6.92 0.62B 0.15 to 0.90 LSD0.05 0.38 0.056

Different letters in columns represents significant differences between population of parameters.

Average N for softening curves representing data for 18 d collected at 6 d intervals were slightly different (P < 0.05) from N values representing duration of 21 d at 3 d intervals (Table 7.1). GL dependent parameters (% and N) for data collected over 18 d (at 6 d intervals) remained strongly correlated (for %r = 0.94; for Nr = 0.93) with the fitted values for 21 d data collected at 3 d intervals (Appendix 5). Overall, comparison of the mean curves show a similar shape for 21 and 18 d collected at 3 d intervals and 18 d with 6 d intervals (Figure 7.3A, B and D). Reduction in storage duration to 15 d with 3 d intervals slightly reduced the expression of lag phase of softening curve (Figure 7.3C).

18 day - 6 day intervals

0 5 10 15 20

15 day - 3 day intervals

Time (days)

0 5 10 15 20

18 day - 3 day intervals

0 5 10 15 20

21 day - 3 day intervals

0 5 10 15 20 Fi rm ne ss (kg f ) 0 2 4 6 = 0.31 = 5.03 = 73.41 = 0.67 = 0.24 = 5.23 = 19.36 = 0.49 = 0.14 = 5.4 = 12.55 = 0.43 = 0.35 = 5.32 = 35.88 = 0.62 A B C D

Figure 7.3: CG fitted mean curves of AFL softening data collected in 21 (A), 18 (B), 15 (C) day with 3 day intervals and 18 day with 6 day intervals (D).

Different data collection patterns did not substantially change the correlation of firmness change parameter (N) in AFL with firmness (SF value) after 100 and 126 d of optimal storage (Table 7.2). These results suggested that AFL monitoring duration

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could be reduced without affecting the relationship of firmness change parameter with firmness loss in optimal storage. Reducing storage duration can affect the GL dependent parameter values and their ranges for fitted softening curves. The different ranges of N for data collected in reduced AFL monitoring durations indicated that new thresholds (Nαand NE) to categorise GLs for 1 of 3 storage potential categories will be required.

Table 7.2: Correlation coefficients (r) of firmness change parameter (NN) of curves

representing different data collection patterns in AFL monitoring with firmness in optimal storage.

Nof curves representing different data collection patterns (day)

Correlation coefficient (r) with SF values in optimal storage

100 day 126 day

21 -0.53 -0.45

18 -0.54 -0.46

15 -0.51 -0.45

18 (with 6 d intervals) -0.51 -0.47