April 1999

In the past six months, since I distributed the last update on the program, we have made dramatic progress in a number of areas. Please take a little time to review the contents below, and I would appreciate any comments or suggestions you might have. If you have inquiries on specific topics please let me know. In particular, there are opportunities for growers who might be interested in planting cooperative trials of CG series rootstocks over the next two years that you might want to consider (section III, below).

I. Program overview

It is now just over a year since I joined the project, and I now have enough perspective on the operations to make breeding decisions based on trial data and observations. To streamline the project we have prioritized all of our orchard, stoolbed, and nursery fields, and have eliminated those that no longer serve our objectives. With the size of the operation significantly reduced (6 fewer orchards, 6 fewer stoolbed fields) we can focus more effort on performing high quality experiments and growing the best possible plant material. We are continuing our efforts to convert the data into a searchable database format, and this will assist us in tracking materials over time and space. We will also be working to develop a USDA-ARS hosted website that will be a source of information on all the publicly available rootstock genotypes in the US. Over the past winter we have analyzed several years= trial data, and have eliminated a large number of genotypes from further consideration (>500). This will allow us to make room for evaluations of more promising genotypes in earlier stages of evaluation.

In the last update I included an outline of the breeding evaluation program (the 10 stage, approximately 30 year process) that explains how the program functions and provides a perspective on the time and the plant numbers that are required to operate a world-class rootstock breeding operation. If you did not receive this you can view it on the www at http://www.nysaes.cornell.edu/hort/faculty/johnson/stages.html, or I can send it to you personally at your request. Since then I have consolidated data on all the elite genotypes in the program and have assigned them to the appropriate stage in the breeding program. Here is a snapshot of the types of materials in the breeding program. We have a total of 90 genotypes in the intermediate and advanced stages (stages 4-10) of the program, ranging from M.27 (size class 1) to somewhat larger than MM.111 (size class 8) in size. Of these 90 genotypes.

All of the genotypes released from the program provide improved tolerance of fire blight compared to other rootstocks. Below (section II) you will read about our efforts to verify the hardiness level and the Phytophthora sensitivity of all commercially available apple rootstock genotypes. The results from these screens will be made available publicly through the Internet, publications, and presentations. Last summer we reported on our molecular marker analysis of a series of rootstock genotypes that were suspected of being misidentified, and we now have much greater confidence in the correct identity of many of the genotypes distributed from the program. However, because of experimental limitations with the molecular markers, we will need to carefully observe several remaining elite genotypes to ensure that they are true to type.

As I have mentioned before in previous program updates, the new cooperative agreement that re-established the Cornell-Geneva apple rootstock program also changed the focus of the program. In addition to breeding new rootstock varieties, we have the responsibility to perform unbiased evaluations of genotypes from other breeding programs and to make this information publicly available, as a service to the domestic apple industry. In order to perform these evaluations we must have the plant material of these new varieties established (with appropriate non-distribution agreements) in Geneva, and this requires agreements with the nurseries and agents that wish to promote their varieties. We have had excellent cooperation with the nursery industry, and we would like to be available as a source of unbiased evaluation data on new rootstocks. Therefore I encourage anybody seeking to introduce new apple rootstock varieties to the US market to make cooperation with the Geneva program a high priority from the earliest stages.

II. Specific projects

A. Commercial stoolbed trials
We began the commercial stoolbed trials in 1999 with two goals: to provide nursery operators with an opportunity to evaluate the most elite rootstock genotypes from the CG series for their propagability. In addition, the cooperating nurseries will generate sufficient plant material under ideal conditions to allow semi-commercial scale testing of elite rootstocks prior to full commercial release. We plan to distribute the 5 most promising genotypes each year to rootstock nurseries, which will then supply our other cooperating rootstock nurseries with plant material to establish stoolbeds 5 to 10 years prior to commercial release. TRECO and Willow Drive nurseries in Oregon and Washington, respectively, perform this work as a courtesy. In 1999 the 5 genotypes were:

• CG.041 B M.9 B M.26 sized, productive, precocious, and fire blight resistant
• CG.210 B M.7 sized, productive, easier to stool thanG.30, fire blight resistant
• CG.707 B MM.106 sized, extremely productive, precocious, fire blight resistant, thick, vigorous liners, heavily branched
• CG.179 B M.26-M.7 sized, productive, precocious, fire blight resistant, thick liners, heavily branched
• CG.935 B M.26-M.7 sized, productive, precocious, fire blight resistant

B. Phytophthora tolerance screening
The International Dwarf Fruit Tree Association (IDFTA) has funded our proposal to evaluate apple rootstock genotypes for their relative resistance to Phytophthora root rots. We began protocol that includes inoculations with 4 different strain mixtures of Phytophthora in the Geneva greenhouses and subsequent measurements of relative growth rates between inoculated treatments and uninoculated controls. In addition, we are simultaneously evaluating a group of new rootstock genotypes from East Malling, Poland, the Czech Republic, Russia, and France in a European Phytophthora field trial. The results from these tests will be available on the internet, and/or in a later edition of this program update. This work is performed in cooperation with Wayne Wilcox and Herb Aldwinckle from the Plant Pathology department in Geneva, and Marie-Helene Simard of INRA, Angers, France. It is also supported through in-kind donations of land and labor, and plant material from Janssens Nursery, Nederweert, the Netherlands, and through donations of plant material from Davodeau Ligonniere and Pepinieres du Valois in France.

C. Replant tolerance screening
International Dwarf Fruit Tree Association (IDFTA) has funded our proposal to evaluate apple rootstock genotypes for their relative resistance to replant diseases. In the first year of the project we will be measuring the relative growth rates of rootstock liners planted in pasteurized versus unpasteurized preparations of field soils with documented replant problems in New York. In the second year we will evaluate the same group of genotypes using field soils from Washington State. The results from these tests will be available on the internet, and/or in a later edition of this program update. Genotypes that demonstrate the best performance in the pot-soil test will be used for orchard trials beginning in 2001.

D. Cold Hardiness screening
The IDFTA also funded our proposal to evaluate rootstock genotypes for their cold hardiness. The incidence of low temperature injury to rootstocks is very time-specific. In mid-winter, when trees are fully dormant, they are capable of surviving extreme cold. However, the same temperatures in the early or late winter, when trees are more physiologically active, would be much more likely to cause injury or tree death. Therefore the hardiness of these genotypes is a multi-part question. How much cold can the roots endure while fully dormant? How much cold can the roots endure while breaking dormancy (late-winter freezes)? How well is the timing of bud break correlated with the late-winter hardiness? Does freezing injury result in significant long-term harm to the plant? We will be researching these questions as part of this project. The mid-winter hardiness ratings are being performed in cooperation with JP Prive, Charlie Embree, and Dale Hebb at AgCanada. We are screening rootstocks for timing of bud break and response to late season freezing in Geneva. Following 2 years of these trials, we will be selecting the best and the worst genotypes for field-level trials with finished trees in cooperation with Martin Kaps from Southwest Missouri State University, a region that regularly experiences wide temperature fluctuations during dormancy. We will be evaluating about 20 genotypes each year.

E. Fire blight screening

1. Pennsylvania
We have initiated a project with Jo Ritter, Jim Travis, George Greene, and Robert Crassweller at Pennsylvania State University, and Jay Norelli at Cornell (Geneva). We provided these researchers with liners of 13 elite genotypes to evaluate their response to fire blight infection through direct inoculation of growing own-rooted rootstocks as well as inoculation of scions on orchard trees. This work was funded as part of a USDA special grant.

2. Geneva
Herb Aldwinckle and Jay Norelli, plant pathologists/biotechnologists and fire blight specialists from Geneva, have a group of experiments evaluating the rootstock phase of fire blight infections. In the past resistance to fire blight was evaluated through direct inoculation of the vegetative tissue of rootstock genotypes. However, it is the reaction to the bacteria when infected through the scion that is the most critical to the growers. Jay=s research will help us to determine how well our traditional evaluation methods in the breeding program correlate with disease development in orchards.

3. Geneva
During this growing season we will resume fire blight screening of rootstock genotypes in the stoolbeds. All our elite genotypes (those in stages 5-10, both CG series and genotypes from other programs) will be inoculated with 2 or more strains of fire blight bacteria, and then evaluated for their tolerance based on the vegetative symptoms. The ratings for these tests will be made publicly available.

F. Virus tolerance screening
As you read about in my previous update, one of our commercially available rootstock cultivars exhibits a hypersensitive response to infection by at least one latent virus (G.16, a fire blight resistant M.9 competitor). Because these viruses are transmissible only by grafting, they are not a threat to growers (unless they are topworking trees in their established orchards). Infected trees slow growth dramatically, become chlorotic, and form a necrotic tissue layer at the graft union that causes the scion to break off easily. Usually these trees will not be harvested from the nursery. Using only virus-free budwood can prevent the problem entirely. In 1998 we began budding trees for all elite rootstocks with scions known to be virus infested. In the future we should know which rootstock genotypes are hypersensitive to latent viruses before they are commercialized, so that nurseries have an opportunity to avoid latent virus problems.

III. New Intermediate and Advanced stage rootstock trials.

1. Washington State:

We have begun an ongoing program in cooperation with Bruce Barritt at WSU and Jim McFerson at WSTFRC to perform simultaneous intermediate stage orchard trials in New York and Washington state. This work is funded by the Washington State Tree Fruit Research Commission and the International Dwarf Fruit Tree Association. The Washington trial will be a requirement for any new CG series rootstocks prior to commercialization, and will allow growers in this region to have a preview of some of the promising rootstocks that may be available in the future. The trials will have 10 trees each for approximately 10 genotypes per year. In 1999 we are planting (in approximate order from smallest to largest) CG.041, M.9, CG.214, M.26, CG.202, CG.206, CG.879, M.7 EMLA, CG.210, and CG.046.

2. Michigan State:

We are planting another intermediate stage trial in cooperation with Ron Perry at MSU. In the future we would like to obtain funding for this so that Midwestern growers have an opportunity to preview up-and-coming varieties as early as possible, closely following the Washington State trials. We will plant 5-15 trees as available. In 1999 we are planting (again, in approximate order from smallest to largest) Bud.9, P.14, CG.247, CG.757, CG.701, CG.206, CG.202, CG.087, M.7, G.30, and CG.760.

3. Europe:

As a result of a meeting this past August with the European Cornell-Geneva nursery cooperators, we have planned a rootstock trial that will be planted in multiple sites across Europe in 2001. This work is being supported by the nursery cooperators, and is being hosted by a European Community concerted action group. The trial will be similar to NC-140 with up to 8 participating countries, and will include G.11, G.16, CG.007, CG.013, CG.041, and CG.202, all genotypes with a range of approximately 30-55% the size of standard seedling rootstocks.

4. Looking for a good home in spring 2000

We expect to have three grower-cooperator trials available. These CG. series rootstock genotypes are all being considered for commercialization in approximately 5-10 years. Criteria for choosing the locations of these trials will include the site (preferably in a region where these genotypes are not currently under trial), and the quality of the data that can be provided by our grower-cooperators. Trees will be furnished free of charge in exchange for the yearly reports of tree production, size, and any anomalies.

1. The first is a semi-dwarf (M.7 competitors) trial with CG.179, CG.202, and M.7, 30 trees each with Ginger Gold.
2. The second semi-dwarf trial has CG.179, M.7, G.30, and CG.707, 20 trees each with Schlect Spur Red Delicious.
3. The third is a broader trial with Improved Golden Delicious as the scion, and ten rootstocks ranging from M.27 to MM.106 size: G.65, CG.041, M.9 EMLA, CG.013, M.26 EMLA, CG.179, CG.210, MM.106, and CG.707, 10 trees each.

5. Looking for a home in spring 2001,

1. 8 rootstock genotypes in M.27-M.9 size class with Cripps Pink (Pink Lady), 30-50 trees each on M.27, P.22, G.65, P.16, B.9, M.9 EMLA, CG.041, G.16. I would prefer that this trial be at a hot site such as central California:
2. Also looking for a home in spring 2001 are 9 rootstock genotypes in M.26-M.7 size class with Ginger Gold, 30-50 trees each, on M.26 EMLA, CG.202, CG.179, CG.156, Pi-80 Select (Sup.4), M.7 EMLA, G.30, CG.814, and CG.210, preferably for a warm humid climate such as the Mid-South, Virginia, or the Carolinas:

IV. Presentations & meetings

A. NC-140
In November I attended the annual meeting of the NC-140 rootstock research group. This organization performs standardized orchard trials of rootstocks for fruit crops across the United States. In 1999 NC-140 will be planting a new trial in 18 states with the Supporter series rootstocks (1-4), Malling series checks, and ten Geneva series rootstock cultivars (the released rootstocks G.16 and G.30, the five stage seven rootstocks from section II.A., and CG.013, CG.202, and CG.814).

B. WSHS
In December I attended the 1998 meeting of the Washington State Horticultural Society in Yakima, Washington. This was an opportunity for me to interact with the regional apple industry and to discuss many of the collaborative projects I have described above.

C. Kearneysville
In February Todd Holleran and I visited the Applalachican Fruit Research Station in Kearneysville, West Virginia. This allowed us to deliver the remaining plant material from Jim Cummins' pear rootstock program to Richard Bell, the USDA-ARS pear breeder, as well as to meet with a group of scientists to discuss potential basic research projects. While visiting I presented a seminar on our activities in the breeding and evaluation program.

D. IDFTA
The IDFTA held its annual meeting in February in Hamilton, Ontario. This meeting was an opportunity to meet industry representatives and researchers from around the country and the world. I made a presentation to the general meeting of the organization that outlined the breeding and evaluation program and our current and future activities.

E. Michurinsk
Mhurinsk is the home of the MGSXA, a national agricultural research center in Russia. MGSXA was the home of the well known Russian apple rootstock breeder, Budagovsky, and continues to operate a large apple rootstock breeding program. The rootstock genotypes from the Michurinsk Academy continue to generate interest in the US because of their winter hardiness and high productivity. The MGSXA will be hosting an international conference on rootstock breeding in late June, 1999. Because of severe economic problems at the academy, they were unable to publicize this event well in advance. If I am able to find some support for the trip (which we learned of in the US only after finalizing annual travel plans), I will attempt to participate in this meeting. The proceedings will be in Russian, but I happen to have studied Russian some years back, and hope to be able to communicate.

F. ASHS
In July 1999 I will be attending the annual conference of the American Society for Horticultural Science. This is a meeting primarily for researchers and will be an opportunity to discuss basic scientific research projects on rootstock related topics. I will be presenting a poster that describes our work evaluating the graft union strength of apple rootstock/scion combinations.

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