Using early‐season measurements to estimate fruit volume at harvest in kiwifruit

Abstract

The results of controlled environment experiments and a field survey covering six major New Zealand kiwifruit (Actinidia deliciosa) growing regions over 3 years showed, surprisingly, that the effect of temperature on the rate of fruit growth is small, at least during the second half of the fruit growth period. The considerable variation in the mean and standard deviation of fruit volume at harvest observed in the field among seasons and sites is therefore not attributable to temperature differences during the fruit-growing season. This raises the possibility that most of the factors affecting fruit growth rates may be established early in the season, so harvest fruit volumes can be predicted from early-season measurements. Mean fruit volumes observed in the field survey ranged from <85 ml (Kerikeri 1987 and Te Puke 1989) to > 130 ml (Kerikeri 1988 proportion of this should be attributed to management practices such as fruit thinning. The fruit growth curves could be described by a two-phase curve, with a reduction in slope 50-60 days after flowering. The initial phase, up to 50 days from flowering, produced growth rates of 1.55 ml/day. The second, slower phase of growth, averaged 0.42 ml/day over the period to harvest. A simple linear regression model was used to predict the mean fruit volume at harvest from measurements of fruit volume made at a given time during the period from 50 to 110 days from flowering (typically mid January and mid March, respectively). The percentage of the variation in mean fruit volume at harvest accounted for by the regression was 75% when based on measurements made 50 days from flowering and rose to nearly 98%, 110 days from flowering. A similar approach was used to predict the standard deviation of fruit volume at harvest. The observed standard deviation at harvest varied from 10 ml to just over 20 ml, which is within the range published by others. The regression of the standard deviation of the fruit volume at harvest on the standard deviation of fruit volume earlier in the season accounted for more than 80% of the observed variation from 50 days after flowering onwards.

Sink priority on ‘Hayward’ kiwifruit vines

“…We have yet to identify the factors that determine this variation in fruit size potential; however, it is likely that this potential is established during the early part of the season. Hall et al (1996) have shown that 75% of the variation in fruit volume at harvest is determined by 50 days after flowering. The first 58 days is also the period when most cell division occurs in kiwifruit (Hopping 1976), and thus the amount of cell division during this period may be directly linked to fruit size at harvest.…”

“…Hall et al (1996) reported that c. 75% of the variation in mean fruit volume at harvest was already determined by 50 days after flowering. By this time the majority of cell division has been completed (Hopping 1976) and the second, slower phase of fruit growth is starting although this is only about a third of the way through the fruit growth period.…”

Flower quality and fruit size in kiwifruit (Actinidia deliciosa)

“…The low importance of ovary weight (i.e., "starting capital" for fruit growth) across seasons and regions, implies that the differences in fruit size at Day 50 that are found to be highly correlated with fruit size at harvest (Hall et al 1996) are the result of something that happens either: (1) after flowering and during the first 50 days of fruit growth; or (2) before flowering but is not expressed during the first 50 days of fruit growth; or (3) before flowering and is expressed before flowering but was not detected by our measurements.…”

“…Hall et al (1996) found that c. 75% of the variation in mean fruit volume and 80% of the standard deviation at harvest were already determined by 50 days after flowering. This is about the time that the second, slower phase of fruit growth starts and is only one third of the way through the fruit growth period.…”

“…As the fruit size at harvest has been largely determined by 50 days from flowering (Hall et al 1996), it must be an expression of differences that exist earlier than that, possibly by the time of fruit set. The objective of this study is to explore variability in flower quality between seasons and regions, and seek relationships with fruit size at harvest.…”