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Nurse Nut Grafting Project

In January, 2000, the group performed over 100 Nurse-Nut Grafts using a variety of nut sources, scion scources and grafting techniques. Our success rate on this first "pilot production" was only about 20%, which is still far short of our 2001 yield target of 75%. We plan to expand our production to 250 nut grafts per year beginning in January 2001, using a new greenhouse being built in Pleasanton, CA. Our gating factor in 2001 will be our limited supply of scions from attractive and blight-free trees, and our limited supply of American Chestnut seeds. As our successful clones from this year grow, our supply of scions will increase geometrically and we will be eventually be limited only by the supply of willing hands. If you would like to participate, don't be bashful.
For more details, contact us via email.

Controlled Crosses

Every summer, we selectively crossbreed several dozen Chestnut trees. Some crosses are accomplished the old-fashoned way; by placing corn pollen bags over the developing female burrs to exclude all but the desired pollen, then, at the optimum time, introducing the desired male pollen inside the bag and resealing. This approach usually yields one nut per bag, or one nut per hour of work.
The second technique is to plant desirable hybrids in a sea of American chestnut trees. When the male catkins appear on the hybrid trees, they are all stripped away, leaving American pollen as the only source for fertilization. As a result, all nuts are known to be fertilized with American pollen. This approach yield about 10 nuts per hour of labor.

Micro Seed Orchards

Scions from several different high-resistant F3 trees, ( one-half American hybrids ) B2F2 trees ( seven-eighths American hybrids ) or B3F2 trees ( fifteen-sixteenths American hybrids ) are planted in a close cluster isolated from other contaminating sources of chestnut pollen. As the trees mature, they produce seeds for highly blight-resistant rootstock. Most micro seed orchards are two to five trees and contain scions from two or three mother trees. If you have suitable land for such a micro-orchard, and would like to participate, contact Charlie A Allen.

Title: What I Did With My Children's Inheritance

Authors: Charlie A Allen & Bernie Monahan; October 2001

Preliminary results of grafting experiments using American-Oriental hybrids on American chestnut rootstock indicate that there may be a tight linkage between graft compatibility and blight resistance.

Hypothesis: The chromosomes involved in the observed graft incompatibility of Oriental chestnut trees are independent of the two pairs of chromosomes involved in blight resistance.

The Oriental chestnut is well known to exhibit graft incompatibility, to the great detriment of commercial growers. Studies of this effect have generally led to a simplified model for the growth enzymes in the bark of a growing chestnut tree that segregate the growth enzymes into six distinct groups. All American chestnuts have a single enzyme type, called Type a. All European chestnuts have a different common enzyme, called Type b. Oriental chestnuts have one or more of four remaining enzyme types, called Types c, d, e and f. Grafts among pure American trees are generally successful, since they share a common enzyme. Similarly, grafts among European chestnuts are generally successful, for the same reason. Grafts among Oriental chestnuts are generally unsuccessful, unless special care is taken to match the parentages of the rootstock and the scion. However, if the parentages match, a vigorous, long-lasting graft between Oriental chestnut trees results. For hybrids between American, European and Oriental chestnut, the results are more unpredictable, but are consistent with one or two pairs of chromosomes controlling the growth enzyme.
Blight resistance in Oriental, European and American chestnuts and their hybrids has been studied more rigorously. The prevailing theory is that two pairs of partially-dominant chromosomes control the degree of blight resistance. American and European chestnuts have virtually no resistance, while Oriental trees with a full compliment of genes for resistance are generally highly blight resistant, regardless of the source of the remaining chromosomes. Thus, a tree that is nominally seven-eighths American and one-eighth Oriental may have blight resistant anywhere from negligible to highly resistant, depending only on those four critical chromosomes. There has been no suggestion in the literature that these two genetic traits; graft compatibility and blight resistance, are linked.

If we are to select scions from highly blight resistant B2F2 trees, we would expect that all such scions have four chromosomes in common; the two pairs that convey blight resistance. The remaining forty ( more or less ) chromosomes would be expected to be made up of 5 chromosomes ( on average ) from the Oriental ancestor and thirty six ( on average ) from the various American ancestors.

If the two traits discussed above are truly independent, then we would expect one-fourth of our scion sources to have a single gene for one of the four Oriental growth enzymes, one-sixty-fourth to have both genes for Oriental growth enzyme and the balance to have both genes for the American enzyme. From a population of five B2F2 trees, we would expect four of five to produce vigorous grafts on American rootstock, one to produce weak grafts, and only if we were very unlucky would we have one source that was profoundly graft incompatible.

Healthy dormant scions were obtained from five B2F2 trees which have proven high levels of blight resistance, derived from the Clapper Tree. Thus, all scions were believed to contain the same two pairs of chromosomes for blight resistance. We had no expectation that any of the other chromosomes were distributed other than randomly from the Oriental and American ancestors; three to seven chromosomes from the Oriental ancestor and the balance from the various American ancestors.
Twenty scions from each source tree were whip grafted onto healthy dormant pure American rootstock, fifteen onto two-year seedlings growing in pots and five onto branch tips of eight-year old trees growing in a grove. In addition, twenty control grafts of pure American scions were made to similar rootstock.

One hundred percent of the B2F2 grafts failed totally, in that not a single bud broke, not a single leaf grew. Twelve of the twenty controls developed vigorous grafts, three produced weak grafts that failed to exhibit vigorous growth and the remaining five failed totally.

The simplest explanation for the above result is that growth enzyme and blight resistance are not independent as we had assumed, but in fact are tightly linked. From an evolutionary standpoint, it is reasonable to postulate that the various Oriental growth enzymes evolved specifically to thwart the chestnut blight, which was endemic in the environment of the Oriental chestnut, while the American and European chestnuts had no such pressure to evolve.

Planned Work For 2002
The first step is to confirm the results described above, using the same five scion sources and more controls.

May 2003 Update

We whip-grafted 100 combinations of scions and rootstock. All rootstock had grown at least one year in 4X4X24 inch pots. The first 21 grafts of hi-resistant hybrid scions on American rootstock were done in November 2002, following the suggested method of Dr. John Shafer, grafting in the fall as soon as both the scion and the rootstock have gone dormant. The grafted material is moved to a warm damp dark environment to allow the graft to knit before bud break in the spring. All grafts failed!
In January, 44 more grafts were made using thoroughly dormant scions and rootstock, and moving the grafts into a warm, damp dark environment for five weeks before moving them outdoors.
In February, 33 more grafts were made. These grafts were kept outdoors.
Results: Hi-resistant hybrids on American rootstock - No success in 16 grafts
Moderate resistance hybrids on American rootstock - 3 of 21 success
Hi-resistance hybrids on Fort Ross hybrid seedlings - 10 of 13 success
Fort Ross pure American scions on pure American rootstock - 15 of 20 success
Hi-resistance scions on (BC3-F1) hybrid rootstock - 3 of 4 success
Conclusion: Grafting success depends critically on matching the rootstock enzymes to the scion enzymes. Even though the hi-resistance scions were, in theory, seven-eighths American, they have the Chinese growth enzymes in their bark. This is what gives them resistance to the blight and also makes them incompatible with pure American rootstock.
Plan for 2004: We plan to collect many, many more hybrid nuts this fall to grow as rootstock for our 2005 grafting experiments.
Thought for the day: That is really a light at the end of the tunnel, and not a bear with a flashlight as some had feared!
UPDATE 15 November 2003

We plan to resume our experiments with nut grafting, applying what we think we learned about the link between graft compatibility and blight resistance. Stay tuned !

Last updated: 15 November 2003 by Charlie A Allen


Fort Ross, CA Plantings

Two groves of American and American-Oriental Hybrids have been planted midway between Jenner and Fort Ross, on the Northern California coast. The first grove was planted in 1994, and contains about 50 trees in a grid; Americans in six rows of six, interleaved with various hybrids in five rows of five. Land is steeply sloped, facing west, and is about three miles inland from the ocean. Trees receive occasional drip irrigation in the summer months. Typical American trees are twenty five feet tall and six inches in diameter at breast height. Hybrids are shorter and stockier. Several dozen of the hybrid trees produced nuts in 2002. Several of the American trees produced nuts in 2002. The plan is to use many of the nuts from this grove for hybrid rootstock in November 2003.
The second grove has been planted with about one hundred trees over an eight-year time span; 1998 - 2005. Typical trees are five feet tall at this time.

February 2005 Update: A third grove of an acre has been fenced and planted with year-old hybrid seedlings in February 2005. No data to date.

Chico, CA Plantings

These plantings are being conducted by the USDA at the Tree Improvement Center at Chico, CA. Several dozen Oriental and Hybrid trees are in this plot. Soil is heavy clay; drainage is poor. Summer temperatures are extreme, dry winds are frequent in the summer. Several trees should begin to produce nuts in 2001.

Petaluma, CA Project

Four two-year old seedlings of American chestnut whip-grafted with highly resistant B2F2 scions were planted in April 2001 in a "front yard" environment, protected with individual gopher cages and rabbit cages. Unfortunately, these grafts, together with 96 others, failed due to enzyme incompatibility between the rootstock and the scion. ( see 'What I Did With My Children's Inheritance' on this page for details.) Three of the trees were replaced with ungrafted American one-year seedlings in September 2001. The remaining tree, although grossly disfigured by the failed graft, exhibited vigorous growth of two crown shoots, and was left in place.

May 2003 Update - All four trees doing well

Novato, CA Project

Six American chestnut seedlings were planted on a steep suburban hillside. Soil is rich and deep. The tiny trees were protected from gophers, rabbits and wandering deer and livestock, and will receive regular summer water for the first three summers. Seedlings were about one foot tall when transplanted from 4X4 inch by 24 inch deep pots.

Isleton, CA Project.

On Hold

Davis, CA Project.

Ten American seedlings have been planted in various Central Valley locations. Stay tuned for results as they wither and die in the hot summer sun, or maybe not.

February 2005 update: The UC-Davis botany professor who obtained these trees and promised faithfully to report his results has failed utterly to honor his pledge. He has never returned a single fact about his project. For shame !

Fairfield, CA Project

Two pure American seedlings were planted in February 2005 in a semi-suburban setting. No results to date.

Berkeley, CA Project

Two pure American seedlings were planted in a suburban setting in February 2005. No results to date.

Pleasanton Project:

A dozen highly-blight-resistant B2F3s are being grown in 15-gallon plastic nursery pots to see if these will become root-bound and thus enter into early reproduction. The plan is to cross them among themselves and produce highly resistant offspring which can be selected for American timber form to become the basis for a seed orchard outside the blight area. Trees are now 4 feet tall and are expected to produce viable male catkins in 2005.

Last Updated 
5 February 2005
by Charlie A Allen


American & American Hybrid Groves

Corralitos, CA Grove

Our Corralitos American Grove contains about 110 trees, mostly pure American from various locations plus some American-Oriental hybrids. This grove was established in November 1993 using seedlings from Bear Creek Nursery in Northport, WA. After the first summer, the California Pocket Gopher Society discovered that American Chestnut roots are mighty tasty, and half the trees disappeared within a few weeks. We now plant all trees there in chicken-wire baskets two feet deep and one foot in diameter.
American stock includes nut sources from Minnesota, Wisconsin, Allegheny County, PA, and Virginia. Hybrids include F2 Douglas Hybrid seedlings used as rootstock, plus high-resistant B1F2 and B2F2 "trees"; actually they remain small bushes because we harvest all possible scions for our various cloning experiments. Last spring we began planting American nuts directly into Gopher Cages, and hoped to get more vigorous growth without the transplant shock. Results were negative. Seedling did much better if grown in pots for the first year and then transplanted.

February 2005 Update: Trees continue to put on height, some reaching 20 feet, but remain only about 1 1/2 inches diameter at breast height No signs of catkins on any trees in this grove. 

European & European Hybrid Groves

Corralitos, CA Grove

Our Corralitos Grove of European Chestnut trees was established in December 1993, using seedlings grown from various nut sources and consists of about 70 trees. This grove has a western and southern exposure, and gets very hot on summer afternoons. Several dozen seedlings have been top-grafted with scions from pure European trees at Stevens Creek County Park in San Jose, CA and Bidwell Mansion State Historic Site in Chico, CA. Last year we added several American and American-Oriental hybrids to the mix, to see how they survive in the harsh sun and wind. Less than half survived their first summer in the hot sun. None of the remaining Americans survived the second summer on this west-facing slope, although the grove 100 yards away on an east-facing slope is doing well. Blame it on the hot afternoon sun which bakes the soil and scalds the bark on the new growth. 

February 2005 Update: This grove of about 60 small trees continues to thrive and produce nuts with no summer water. 

Shingle Springs, CA Grove

This grove was planted in 1994, and originally held 100 European-Oriental hybrids. Rabbits, deer, gophers, root rot and drought have since reduce the number of survivors to about 25. Our plan is to select a dozen or so to develop into full-sized trees to study their growth in the very hot California sun. Typical daytime temperatures range from 100 to 115 degrees F. in July, August and September, with zero rain and plenty of hot, dry winds. A dozen trees produced European-Oriental hybrid nuts this year.

Other Projects
See the section on Micro Seed Orchards above.

Last updated: 
5 February 2005 by Charlie A Allen