When we started growing and breeding chestnuts here in SE Minnesota, there was no chestnut blight (
Endothia parasitica at first, then
Cryphonectria parasitica; though my own preferred name is
Cryphodothia pseudoparasitica*... long conversation...) known, for at least 50 miles, perhaps 100. It had been identified in Ames, Iowa, and seen once briefly around Zumbrota, Minnesota; but it certainly was not here.
For the first 20 years, as our chestnut plantings expanded, we never saw it. When we were ready to test our chestnut genetics against the blight, we sent seed both to Auburn University in Alabama, and to the Hubei Academy of Agricultural Science in China. Tests in both places were overseen by Dr. Hongwen Huang; I will put his reports here, originally published in our Root & Branch #4:
Date: Fri, 05 Apr 96 11:18:53 EST
From: hongwen huang
Subject: RE: report of blight resistance of your breeding lines in Alabama
Dear Phil:
In response to your request for the results of my
performance tests of chestnut blight (Cryphonectria parasitica) resistance of your advanced breeding lines grown in Auburn, Alabama, the following statement is based on my observations and best knowledge.
As you know, I collected seeds of some 25 trees, representative of your breeding lines in your breeding orchard, and 4 random selections of pure American chestnut at West Salem, Wis. in Fall 1991. Twenty to 50 seeds from each line and selection were germinated in the greenhouse and transplanted in 18.93-liter polyethylene containers in Spring 1992. All seedlings remained in the containers in an outside growing area under daily sprinkler irrigation. This area was a designated plot for my research on evaluation of blight resistance among Chinese chestnut cultivars
using artificial inoculation of virulent C. parasitica strains. Three strains were used: SLA-155 and SLA-389 (provided by Dr. Sandra Anagnostakis, Connecticut Agricultural Experiment Station) and AL-W ( a wild strain obtained in Alabama).
An evaluation for blight resistance was initially started in Summer 1992 and repeated in 1993. Resistance was rated in 4 scales: very resistant, resistant, susceptible-resistant and susceptible. All pure American seedlings were completely susceptible to C. parasitica and were girdled by blight within 3 weeks and died. Variation of blight resistance was found within and between each seedling progeny
of your lines. Most seedlings showed resistance to C. parasitica, ranging from susceptible-resistant to resistant. There were 2-8% seedlings that were completely susceptible and died like pure American chestnuts. To my knowledge, all 25 lines you developed are resistant to C. parasitica, but heterozygotic for at least one gene of blight resistance (2-3 genes involved). Seedlings from each resistant parent line should be expected to segregate for blight resistance genes and the 2-8% susceptible seedlings found in this study should be those homozygotic for all alleles of the related 2-3 genes. This roughly fits the model of 2-3 genes regulating blight resistance. Since this experiment is not formally carried out in an official project, no records are filed and reported. I am personally responsible for the results stated above.
Sincerely
Hongwen Huang
Associate Prof.
Wuhan Institute of Botany
The Chinese Academy of Sciences
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RE: report of blight resistance of your breeding lines in China
Dear Phil:
I would like to give you a report on an evaluation of your advanced breeding lines for resistance to chestnut blight.
Seedlings of the thirty-six hybrid breeding lines you sent to the Hubei Academy of Agricultural Science were planted at 2 x 4 m spacing in an experimental plot of the Fruit and Tea Institute of the Academy in Spring 1992. When I went back to China in June 1994, I evaluated all lines for resistance to chestnut blight in August. All lines looked healthy and have grown very well in Hubei. Most lines were rated as very resistant (defined as canker width = 1.0 to 3.0 mm on the trees when they were infested by the blight) to resistant (canker width = 3.1 to 5.0 mm). The resistance observed on these lines is comparable to what is usually found in resistant pure Chinese chestnut.
The cankers on these lines were gradually walled off after the initial infection. If you have further inquiries regarding the performance of your breeding lines in Hubei, P.R. China, please don't hesitate to contact me or Professor Zhang at the Fruit and Tea Institute, Hubei Academy of Agricultural Science.
Best regards
Hongwen Huang Ph.D
Associate Professor
Wuhan Institute of Botany
The Chinese Academy of Sciences
The test orchard in China is still growing there, and was also inspected by Brandon Rutter during his work in China some years back. Most of the trees are thriving, the primary complaint of the managers there being that some of the local folks insist on climbing over their razor wire fences to steal chestnuts from our trees. Hubei is a major chestnut producing province, so that's really quite a compliment.
Being quite familiar with the blight, and knowing it was only 50-100 miles away, I always expected it to get here in my lifetime. And now, it has.
Although I certainly know chestnut blight when I see it, I nonetheless asked MN State Forest Pathologist Ed Hayes to come and do the positive identification. This is his photo, in fact. It's the blight.
It showed up first on one of my "canaries in the coal mine". At the outset, expecting blight to arrive, I planted pure American chestnuts in two locations on the farm, expecting them to show any blight presence sooner than the resistant and semi-resistant hybrids. One on the north fence, where they are reproductively isolated from the hybrid breeding work; and a small population of male-sterile pure Americans among the hybrids. It was one of those male-steriles that showed it first.
This tree took 3 years to kill to the ground, and is now re-sprouting vigorously, as American chestnuts do. In those years, we've started to see blight elsewhere among the hybrids, a few trees succumbing slowly; a few with an affected branch. Most show no signs, but in the nature of epidemics, the true testing is yet to come. The blight is now here, permanently; as expected. More trees will die in the coming years.
Most folks respond "oh, that's terrible!" when we tell them; but we don't feel that way at all. It was expected; we prepared for it; and in fact we can now directly test our newest hybrid chestnuts against the blight right here, and all their lives long (the only kind of testing that counts in the real world). In many ways it's a relief.
But - it does mean that our chestnut tubelings can no longer be expected to be blight free (although they probably are); and should not be shipped to or planted in areas still free of the blight, to protect any susceptible trees still living in such places.
And it means visitors should be careful about carrying blight from here back to uninfected areas. It doesn't mean you shouldn't visit; just that you should be careful about what you touch, be sure to disinfect shoes (chlorine bleach is the standard), and generally think about what you do when.
*The blight fungus in this case is not actually a "pathogen" or parasite, an organism that causes disease for a living. In China it mostly lives as a free-living "saprophyte", an organism that lives by breaking down dead matter. It lives that way in North America, too; extremely well. Judging from the infection patterns we see in our plantings, that's most likely how it got here. Not from some visitor bringing a disease; but just as the natural spread of an invading fungus, slowly taking over more territory. It grows quite well on oak bark, and in forest litter; it's here to stay.
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