The cross-fertilization of ideas across the worldwide growing community has . . . led to
some interesting and successful hybrid systems.
for New Zealand?
HortResearch
Nelson Research Center, Motueka, New Zealand
ndAnnual IDFTA Conference, February 20-24, 1999, Hamilton, Ontario,
Canada.
INTRODUCTION
For many years the New Zealand apple industry has relied upon production from the
intermediate vigor rootstocks MM.106 and M.793 with trees planted at 5 x 3 m, 666 trees/ha
(16.4 x 9.8 ft, 270 trees/acre).These orchards have produced some of the highest recorded yields
in the world, e.g., Warrington (1994) quoted a yield of 163 t/ha (71 ton/acre) from a mature
orchard of Granny Smith.Although the planting density has not changed greatly in New Zealand
over the last 30 years, there has been considerable improvement in yield and fruit quality with
the change from multi-leader trees to center leader trees and thence to slender pyramid training
(Tustin et al., 1990).At the same time the New Zealand industry has been one of the world
leaders in the rapid introduction of new cultivars, e.g., New Zealand production of Granny Smith
and Red Delicious has fallen dramatically since 1988 and been replaced by Royal Gala and
Braeburn.These changes to cultivar mix and production methods have undoubtedly improved
the economic well-being of the fruit industry.New Zealand’s production, however, is dominated
by the export market and therefore is very sensitive to the increase in the world apple supply
generally and specifically to alternative suppliers of cultivars such as Royal Gala, Braeburn and
Fuji.In light of the long distance to the consumer markets for New Zealand’s products,
economic viability can be maintained only by continuing to hold a position in the market for
premium rather than commodity produce.This will be achieved by 1) the rapid introduction of
new cultivars, 2) further improvements to fruit quality and 3) reductions in the costs of
production.This paper examines the possible role of more intensive planting systems on
dwarfing stocks assisting the New Zealand fruit industry toward these ends.
DRIVERS FOR HDP
Elsewhere in the world, there has been widespread uptake of intensive plantings on dwarfing
rootstocks, particularly in NW Europe and more recently in North America.The adoption of
these systems has been in response to economic pressures for improvements to fruit quality, the
rapid introduction of new cultivars, reduced production costs and reduced spray drift.Before
any widespread adoption of intensive planting systems occurs within an area, however, a number
of key drivers need to be in place.
A Demonstrated Advantage over Existing Methods
Growers in general tend to be somewhat skeptical of results from elsewhere in the world or from
research plots in their own country being directly applicable to their own situation.It is,
therefore, the innovators within each industry who lead the way, aided and abetted, by the
scientists and extension services.
Availabilityof Dwarfing Rootstocks
The availability of newer rootstocks can be delayed by quarantine regulations or a nursery
industry that lacks a vision of what rootstocks will be required in the future.
Economic Pressures
There is undoubtedly a reluctance on the part of growers to make wholesale changes to their
existing systems of production if there is little perceived economic incentive to do so.
Unfortunately, like the story of the frog in the pot of water, the heat can gradually increase until it
is too late.Pipfruit growing is both a long-term and risky business so the grower must be
studying current changes both in his/her own backyard and elsewhere if the business is to remain
viable.
New Cultivars
Part of that study involves the selection of new cultivars that will give improved returns over his
existing mix.Growers must consider not just the profitability of their existing orchards but
whether that profitability could be enhanced by replanting with new cultivars.The high price per
kilo for new cultivars has acted as a strong catalyst for intensive systems on dwarfing rootstocks
in many parts of the world.
SkillBase
Finally there must be a sufficient understanding of a new system before it can be taken up
successfully.The ready availability of cheap air travel undoubtedly has helped the movement of
growers and advisors and in turn hastened the uptake of new systems.It is much easier to
understand a system by standing next to a good example of it with a disciple of the system
explaining the details rather than reading a third party’s interpretation.The cross-fertilization of
ideas across the worldwide growing community has also undoubtedly led to some interesting and
successful hybrid systems.
THE NEW ZEALAND SITUATION
In contrast to Europe and North America, the New Zealand industry has been slow to adopt
intensive plantings on dwarfing rootstocks despite the current economic pressures of the need for
a rapid introduction of new cultivars, an improvement in fruit quality and a reduction in
production costs, pressures which seem to be common to growers throughout the world.There
are a number of reasons for this reluctance—in some cases the key drivers are missing or poorly
developed—but there are some reasons specific to the southern hemisphere environment.
High Current Yields by Semi-intensive Systems
Reference already has been made to the very high yields obtainable in New Zealand by systems
based on intermediate vigor rootstocks.It is unlikely that single row intensive systems on M.9
could match these high total yields; their advantage will undoubtedly be in the improved fruit
quality and reduced production costs.It is important to note, however, that the 163 t/ha recorded
for Granny Smith was with a cultivar that had no color requirement.Secondly, although multiple
picks do increase the yield of fruit with acceptable color, the internal quality of later picks from
large trees may not be adequate for market requirements in the future.
Lack of Dwarfing Rootstocks in Quantity
Although dwarfing rootstocks such as M.9 were imported into New Zealand many years ago,
these were the virus-infected material.It is only within the last 10 years that virus-free material
Mark was the first virus-free dwarfing stock available in
New Zealand and, although some growers have had excellent results from intensive systems on
Mark, others have found its habits of overcropping, lack of growth and variability disappointing.
More recent dwarfing rootstock introductions have included CG.202, 210 and 179.At present,
nurserymen in New Zealand are not able to supply the requirement for trees on dwarfing stocks.
General Poor Qualityof Nursery Tree
Precocity of intensive systems is not only one of the design criteria, it is also essential to offset
the establishment costs.Precocity undoubtedly can be improved by planting well-feathered
trees.Unfortunately nurserymen in New Zealand have yet to consistently produce large, well-
feathered trees on dwarfing stocks.
Concerns over WoollyAppleAphid
It is easy to forget that one of the main reasons for the breeding of the Merton and Malling-
Merton series of rootstocks was to produce woolly apple aphid resistant rootstocks for the
southern hemisphere producers in the British Empire.Woolly apple aphid infestation of the root
systems of apples caused serious damage in the early part of the century.This was eliminated by
the arrival of the resistant rootstocks.Unfortunately none of the widely available dwarfing apple
rootstocks are resistant to woolly apple aphid so there always has been a concern that susceptible
rootstocks will suffer badly from this pest.Although the parasiteAphelinus maliwas introduced
in the 1930s and is now widely distributed, it parasitizes aphids only on the aerial part of the tree.
Concerns over Sunburn
Undoubtedly one of the advantages of intensive systems is that the fruit is better exposed to the
light with the attendant improvements to fruit quality.In a high solar radiation environment this
may increase sunburn and so the system may fail to produce the desired fruit quality
improvement.
Lack of Experience
There remains in New Zealand a lack of widespread experience and management skills with
intensive systems.
intensive systems would not succeed in New Zealand as they have elsewhere.Dr. Stuart Tustin
at Havelock North had already established a number of systems comparisons of Fuji on MM.106,
M.26 and Mark in a number of sites.Consequently I concentrated on a system I knew well from
Europe, the slender spindle on virus-free M.9.However, with the move toward less chemical
inputs in orchards, I felt that multi-row systems would not be a long-term option, as such systems
depended upon chemical weed control.I was fortunate to arrive just at the time when virus-free
M.9 was becoming available.The clone of M.9 we use most widely in New Zealand at present
was originally introduced from East Malling in the 1930s and heat treated in the mid ’80s. It is
sometimes designated NZ9 to distinguish it from some of the other European clones that have
been more recently introduced, e.g., T337, EMLA9, Pajam 1 and 2.Back in 1991, there was
very limited interest in trees on dwarfing rootstocks.Over the last 8 years, however, there has
been a gradual change and there is now a strong move toward smaller trees by 1) reducing the
height of trees on MM.106 and M.793, 2) the use of M.9 interstem trees on MM.106 and M.793
and 3) the use of dwarfing rootstocks such as M.26, Mark and M.9.In 1991 only 5% of trees
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