Rootstock choices offer powerful productivity tool

Strategic rootstock selection has a key role to play in driving the productivity of the future orchard system, growers at the well-attended spring Future Orchards® walks late last year were told.

Rootstocks, once established, will underpin the orchard for decades.  While it is critical to continue selecting rootstocks based on productivity traits, there will be an increasing need for growers to adopt rootstocks that offer disease resistance.

While current rootstocks such as M9 can provide good productive performance, attitudes towards chemical use will dictate that growers in the future must be less reliant on chemicals for pest and disease management.  Rootstocks that offer disease resistance will have a vital role in helping growers adapt to a less chemical-reliant future.

Trial results comparing the performance of existing and new rootstock varieties, and the latest experiences from Europe and the United States, highlighted the range of valuable traits available.

Southern Loop guest researcher Dr Nicola Dallabetta from Fondazione Edmund Mach (FEM) in the Trentino production region of Italy outlined current rootstock research and the pros and cons of currently available rootstocks, including the new Geneva rootstocks.

On the Northern Loop Tom Auvil from North American Plants, who also farms in the Orondo region in Washington State, USA, outlined trends in production systems, rootstocks and the importance of focussing on revenue rather than cost.

AgFirst consultants Craig Hornblow on the Southern Loop and Ross Wilson on the Northern Loop presented the latest Orchard Business Analysis (OBA) results showing continued improvement in yield and packouts across the model orchard and the significant combined impact on profit that making a number of relatively small improvements to production, packout and price could deliver.

 

Rootstock selection was a focus of the Spring Future Orchards walks.

 

Disease resistance

The clear driver for adopting new rootstocks is for the disease resistance traits. Both international guests agreed that the M9 rootstock had set the global standard for productivity and was still the most widely used rootstock.  However, its susceptibility to woolly apple aphid (Eriosoma lanigerum) and consequent reliance on chemical intervention was identified as a significant issue in light of global trends towards less chemical use likely to result in fewer and less effective chemical control options.  It is therefore likely that a rootstock like M9, which relies on more chemical intervention than newer rootstocks, will ultimately be at risk in a future where a reduced dependence on chemicals is a priority.

“For my institute the main goals are disease resistance,” Nicola said. “Particularly for apple proliferation (Candidatus Phytoplasma mali), apple replant disease (ARD) and woolly apple aphids (Eriosoma lanigerum), all of which are major problems.

“Woolly apple aphid is worsening as a result of climate change, where our winters are much milder helping the woolly aphid overwinter more easily.

“Apple proliferation is worsening as more intensive plantings cause root systems to overlap (root anastomosis) more and leads to the removal of the tree, but later the next tree is then needed to be removed.”

Nicola said apple replant disease (ARD) was a major problem in Italy where the dwarfed M9  rootstocks, sensitive to ARD, was placed back into the exact same planting row over repeated generations.

“Due to the replant symptoms, tree growth is limited, unable to fill up the available space, thus growers are increasing planting density to 6,000 trees/hectare for several cultivars to obtain a sustainable yield,” explains Nicola.

Consistency crucial for uniform canopies

Tom Auvil said that as well as delivering disease resistance, US growers were looking for new rootstocks to also provide better consistency in the block to drive better revenue.

“One of the biggest challenges in making platforms efficient is having uniform canopies,” Tom said. “The cost of doing business in the US has increased dramatically so apple businesses are therefore transforming from being cost focused to revenue focused.

“In the past the big growers were not achieving consistency. Now there is so much money at stake they are seeking out every piece of information for planning and execution of new blocks.”

Geneva® apple rootstocks came out of a research program between Cornell University and the United States Department of Agriculture-Agriculture Research Service (USDA-ARS).  The emphasis of the program was productivity, yield efficiency, ease of nursery propagation, fire blight resistance, tolerance to extreme temperatures, resistance to soil pathogens and apple replant disorder.

While this varies by rootstock, the characteristics of the Geneva® rootstocks are that they are resistant to diseases such as fire blight, crown and root rots (Phytophthora) and apple replant disease.  They are also resistant to woolly apple aphid and have low suckering and burr knots.

The Australian apple industry is already experiencing significant production losses due to apple replant disease, phytophthora, woolly apple aphid and burr knotting.  In the future, as products are inevitably withdrawn, combined with other factors such as climate and increased netting, it is likely these problems will increase in severity highlighting the importance of using rootstocks as a strategic orchard management tool.

“The Geneva rootstock G.41 was judged the top pick of the new rootstocks”

Based on overseas results the Geneva® Rootstocks currently offer Australia the best options for new rootstocks to trial in our conditions.  The Geneva® program has already years ago licensed two Australian nurseries, Graham’s Factree and ANFIC (Australian Nurseryman’s Fruit Improvement Company) for this material to be delivered to growers but so far there has been little demand and due to the lack of critical mass the ability of nurseries to provide this material is low.

Shortage of planting material is not unique to Australia. Tom Auvil said the trend to higher planting densities in the USA was a major factor causing extreme shortages in their plant material.  As a result, growers were looking to new technologies such as tissue culture where under laboratory, then greenhouse conditions, mass production of plants from plant cells could be achieved relatively quickly.

“A grower could get a finished tree with their desired scion and rootstock from the tissue culture company in approximately eight months,” Tom said.  While the trees are a different smaller potted product, it is the lack of availability that is driving this technology in the apple sector as well as in other industries such as stonefruit, citrus, grapes, olives and berry industries.

The Geneva rootstock G.41 was judged the top pick of the new rootstocks due to its superior disease resistance and closest similarity to the growing characteristics of the popular M9.  However, as Tom Auvil explains, while G.41 might be great in the orchard it is a “nightmare in the nursery”.

“It is hard to get a rootstock that is good for both the nursery and the orchard,” he said.  “G.41 is extremely brittle and a large G.41 is a problem – anything above 12mm at the union will be prone to breaking and below 12 mm is ok.”  He said G.41 has been performing consistently across soil types and water quality.

In trials G.11 was far superior to M9 for production producing a higher number of larger fruit however G.11 is not woolly aphid resistant and underperforms on light soils.  G.935, G.969 and AR295.6 were recommended for their precocity and productivity in situations of poor or weak soils or where the scion is weak growing.  Unfortunately the AR295.6 which is a newer Malling rootstock is not available in Australia and G.969 is also not available.  G.11 and G.210 produce larger fruit sizes which is likely due to their capacity for higher water and nutrient uptake.

“All of the Geneva replant tolerant rootstocks will out grow and out yield any of the Malling rootstocks,” said Tom. Horticultural practices make more difference than the rootstock genetics among G.41, G.214, G.969 and G.210.  G.890 is great for replacement trees or with slow to grow scions.  G.202 while it does have woolly aphid resistance will perform poorly producing a tree which is too big with fewer apples with a smaller fruit size.

During the field visits we found ourselves looking at younger apple tree plantings with the same problems.  From the discussions this was represented best by Craig Hornblow “Water, water, water, weeds then nutrition!”  Powdery mildew was also rife across most regions where cupping of leaves is the first early indicator of powdery mildew.  Leaves should be large and flat which was often not the case suggesting much more emphasis must be placed on powdery mildew management.  According to Tom Auvil, young trees should be growing at a rate of 10 to 15 centimetres per week, with 10 cm being a threshold for management correction to increase growth.

Strong participation by growers and the wider industry in the latest walks show that APAL’s Future Orchards® project is continuing a strong momentum, delivering more information to more people towards building a more productive and profitable apple and pear industry into the future.  The latest results from the project’s Orchard Business Analysis bear out productivity gains, showing the average production for apples and pears under the ‘model’ orchard has now reached 49 tonnes per hectare.

When this latest iteration of Future Orchards® was proposed, it was forecast that the OBA model orchard would have an average yield (including young trees) of 45 tonnes per hectare by 2021.  It seems after two years we are already there.  The other major outcome of this project was to increase Class 1 packout to 75pc. Class 1 packouts are already sitting at 70-71pc.

As planned, the focus of the Future Orchards® program in 2018 will now be Future Production (Quality) where we will look at ways to lift Class 1 packout.

Thank you to our guests, FLA’s and AgFirst for delivering yet another quality orchard walk event.

Presentations are available on the Future Orchards Library

The Orchard Business Analysis 2016-2017 report is available to growers by emailing Angus Crawford.


Acknowledgement

Future Orchards is a strategic levy investment under the Hort Innovation Apple and Pear Fund. It is funded by Hort Innovation using the apple and pear levy and funds from the Australian Government, and is delivered by APAL and AgFirst.

By |January 10th, 2018|Future Orchards, News, Varieties and rootstock|

About the Author:

Technical Manager, Apple and Pear Australia Ltd
acrawford@apal.org.au
03 9329 3511