June Dreer Fellowship Report

Melts in Your Mouth: A Fruit that Will Not Disappoint

A consumer gazes across the rows of colorful produce on the supermarket shelves. The rainbow display is appealing to the eye and can make the taste buds water. The consumer selects a piece of fruit and scrutinizes its appearance. It seems flawless, and it is just beginning to soften. It must be perfect eating quality! Yet, upon bringing home that fruit and biting into its flesh, the consumer finds its taste only lack-luster. What a disappointment! If only there was a way of guaranteeing that the rainbow of color would translate into a pleasant eating experience. Well, now it seems that there is a way. Flavor need not be an evasive quality anymore.

Dry matter is the proportion of fruit dry weight – carbohydrates, fiber, organic acids, proteins, lipids, and minerals, to fresh weight – dry weight plus water – in produce. A fruit with high dry matter at harvest will have high soluble solids when ripe. All of this translates into taste. The kiwifruit industry in New Zealand has, in the last few years, put an emphasis on dry matter production – adding price premiums when dry matter is high and rejecting fruit which does not meet a minimum standard. The result is a high-quality product and a successful industry.

The Impetus
The kiwifruit industry in New Zealand is an export industry. In the year 2005, kiwifruit valued at $720 million (USD) was exported from New Zealand to more than 60 countries. Despite this incredible sum, New Zealand still competes with others – namely Italy, Chile, and China – for export markets, particularly those in Japan and Eastern Asia. It is estimated that 80% of New Zealand’s kiwifruit profit comes from 20% of the fruit exported to Japan. The Japanese have proven themselves avid kiwifruit consumers and perhaps even connoisseurs. They are willing to pay upwards of $10 (NZD) per tray of fruit; whereas, markets in the European Union generally pay $3 per tray – just above the break-even mark – and North American, Australian, Eastern European, and New Zealand markets generally pay below the break-even price per tray. Thus, with a Japanese market willing to pay above and beyond, it is important to keep those consumers satisfied. Their satisfaction depends on sweet, delicious fruit.

The Standard
Because the kiwifruit industry is controlled by one supplier in New Zealand - the ZESPRI company – criteria for dry matter and taste were relatively simple to implement. As harvest nears, fruit samples are collected from each block of an orchard and tested for dry matter accumulation. If this fruit meets the Minimum Taste Standard (MTS) for dry matter – a 14.5% average for green kiwifruit and a 15% average for gold kiwifruit – then the fruit can be harvested. Meeting the MTS is not the goal, however. The goal for growers is to achieve the highest dry matter possible with the lowest variability. Using the average dry matter and variability collected from each orchard, and the minimum standards, ZESPRI calculates a Taste ZESPRI Indicator (TZI), a value which is used to distribute price premiums and establish which fruit will be exported to the prized Japanese market. Thus, the strategy is to only send high-tasting fruit to Japan and to pay growers accordingly for their management toward top-quality fruit.

The Management
Because taste has been established as the key parameter for kiwifruit payment, it is important that research on vine management which improves fruit quality take a high priority. As mentioned, however, taste parameters have only been implemented in the last few years; thus, research toward this end is only in its infancy. It is understood that in order to achieve high dry matter, growers must strive to optimize carbohydrate production in the vine, as carbohydrates account for approximately 55% of dry matter. Carbohydrate production depends on such factors as light intensity, moisture availability, nutrition, and genetics. Nevertheless, carbohydrate production within a vine does not necessarily mean that those carbohydrates will be concentrated in the fruit. Therefore, research into the cultural practices which result in carbohydrates concentrating in the fruit are of particular importance.

The cultural practices that appear to influence kiwifruit dry matter are manifold. Choosing the proper rootstock may have an effect, as well as ample pollination. Irrigation must also be well-managed to prevent water-stress while not “watering down” the fruit. Excessive nitrogen fertilizer is a hindrance because it results in disproportionate vegetative growth, which draws dry matter to the leaves instead of the fruit. It also causes excessive crop loading. Environmental modifications, such as ground covers and overhead shelters, are under investigation, but a practice which appears to be particularly successful, at least in the short-term, is vine girdling.

Girdling involves removing the bark down to the cambium layer of either the trunk or individual canes. In the process, the phloem, or sugar-conducting tissue, is removed in a concentric strip preventing downward movement to the roots. When done properly, photosynthates produced in the canopy remain concentrated in the canopy and more are supplied to the fruit. By the time the fruit is harvested, the girdle has usually healed, allowing time before leaf-drop for more photosynthate production to be supplied to the roots for winter storage. Girdling trials, however, are only in their first couple of years, so there is little understanding whether vine roots will be damaged over the long-term by this practice. Some growers remain hesitant to employ the practice until more information is gleaned. Others are experimenting with the practice in small blocks.

Kiwifruit growers in New Zealand are an innovative breed of individuals, willing to experiment. Not only have they tested the cultural practices already mentioned, they are also experimenting with systems of canopy management, in hopes that it, too, will improve fruit quality. Canopy management involves those practices which influence the growth of the vines carrying fruit. It involves pruning and training the vines in such a manner that improves cane quality, determines growth habit, increases light penetration to the fruit, and reduces vegetative vigor. Various canopy management strategies are employed. Many growers are creative modifiers of traditional systems, while others are progressive inventors of entirely new systems. My work here at HortResearch has involved meeting these growers.


The Systems
These last two months, I have been speaking with growers and visiting their orchards to gain an understanding of the various methods of canopy management in Hort 16A – the gold kiwifruit. Because managing vines to promote high dry matter accumulation is a new area of research, and because Hort 16A is a relatively new crop, my project has been challenging but exciting. With the assistance of HortResearch Technology Transfer Manager, Shane Max, I developed a survey to ask growers how they would describe their canopy management schemes, their reasons for using them, the time required to manage their orchards under each system, and how their systems may or may not have influenced dry matter results this year. These are the systems that I have investigated:

Traditional cane replacement. This type of system, as its name implies, has been employed for some time, even before ZESPRI established taste standards. It may fall under two categories based on the type of cane used: primary or stubbed. Primary canes are those that initiated in the previous year and fruited lightly. Stubbed canes are those that fired as a result of a hard cut. Traditional cane replacement is still used by growers, but many are moving away from it in hopes of finding a system that increases fruit dry matter and reduces pruning costs.

Spur-fruiting. Spur-fruiting utilizes a permanent lattice of canes from year to year and crops on small spurs coming off of those canes. This style of canopy management has been adopted for various reasons. Some growers believe that it requires fewer hours to prune. Others believe its strongest asset is reducing vegetative vigor. In cases where vine spacing is large, a permanent structure means that canes will fill their allotted space every year, resulting in higher yields. Growers have also touted that with a permanent framework, stored carbohydrates permit rapid leaf development and canopy fill in the spring.

Low vigor. Utilizing spring initiated, non-vegetative canes is the intent of a low vigor system. Because Hort 16A is typically a vigorous vine, low vigor pruning involves a hard cut-back in the winter months to reduce vegetative vigor. The intensive winter pruning also means that summer pruning is reduced, and thus, pruning costs overall are moderated from traditional systems. Light penetration through the vines to the fruit is also good. Converted growers claim that the low vigor vines result in more carbohydrate storage in the fruit, generating high yields, good size, better than average dry matter, and earlier harvest.

Stringed cane replacement. The stringed cane replacement scheme requires the greatest capital investment, but growers assert that this system improves fruit quality and simplifies pruning so that even unskilled laborers may be employed. A stringed system most visibly differs from the other systems because, while fruiting canes are grown as usual on a wire trellis, replacement canes for the following year are grown up at an angle, trained along strings affixed to a central post or wire above the canopy. Pruning is simplified because in the winter, a pruner can essentially walk parallel to the vine leader and cut off every fruited cane. With this vegetation removed, the strings are cut, and the replacement vines for the following year are already selected and trained. They are laid and tied in the place of the previous vines. The following year, as these vines are cropping, replacement canes are selected from shots that come off at the leader, and these are trained up strings to be the following year’s cropping vines.

Alternate bearing. This system works in conjunction with the stringed replacement system. In this case, vines only crop or produce the following season’s replacement canes, not both. Thus, rows are cropped every other year, giving them a “break” in alternate years to store carbohydrates. This system maintains the same benefits as a stringed replacement system, but growers believe that the stored carbohydrates from the resting year revitalizes the vines and shortens the fruit maturity period the following year, resulting in an earlier harvest.

The Prospects
Having spoken with several growers employing each of these training systems, much information has been gleaned. Our hope is that this survey will prompt further, controlled research where these systems can be compared. The work that growers are doing to develop these systems is invaluable; nevertheless, what is needed is an experiment that can compare these systems, where all other cultural practices are constant. We hope that my work will show that there is a need for such research.

This project has also served to edify my own horticultural knowledge in a crop that was once unfamiliar to me. Speaking with growers required that I establish a foundation of knowledge for the crop and the industry before making my visits. Speaking with the growers gave me practical, first-hand insight.

I have also gained experience in the methods of Technology Transfer which occur here in New Zealand. This experience has been invaluable, given my career interests in Cooperative Extension. Exposure to the means by which knowledge is transferred in New Zealand will provide me with a broader base to draw upon when I enter my own career.

And perhaps the greatest prospect of this work are the implications it has toward producing high-quality, pleasant-tasting fruit. Someday, we will come to expect a vibrant taste from the vibrant rainbow we see on the supermarket shelves. Disappointment will melt away like a perfectly-flavored fruit melting in our mouth.

References

Baker, R. 2006. “Spring Trunk Girdling and Alternate Row Cropping – Testing the Boundaries.” Kiwifruit – New Zealand Kiwifruit Journal. July/August 2006. pp. 27-30.

Dyck, B. 2005. “Understanding Dry Matter.” Kiwifruit – New Zealand Kiwifruit Journal. September/October 2005. pp. 9-11.

Gardiner, C. 2005. “Low Vigour Pruning Hort 16A.” Kiwifruit – New Zealand Kiwifruit Journal. July/August 2005. pp. 22-24.

Gardiner, C. and S. Max. 2006. “Cropping Hort 16A on Spurs – A Success Story from Whangarei.” Kiwifruit – New Zealand Kiwifruit Journal. January/February 2006. pp. 13-15.

Kerr, J., E. Hewett, and A. Aitken. 2005. “HortResearch Fresh Facts – New Zealand Horticulture” (brochure). ISSN 1177-2190. ISBN 0-477-10014-7. pp 1-33.

Mowat, A. 2004. “Principles of Growing Fruit with Superior Dry Matter.” KiwiTech Bulletin #32. Sept. 2004.

“Taste ZESPRI Update.” 2006. Grower bulletin produced by the ZESPRI company. February 2006.

Wright, P. 2005. “The Challenges of Achieving Higher Dry Matter – A Grower’s Perspective.” Kiwifruit – New Zealand Kiwifruit Journal. November/December 2005. pp. 31-34.