INDUCED IMMUNITY TO CHESTNUT BLIGHT

Dr. G. A. Zimmerman, Piketown, Pa.

Several years ago I started out to get rid of the chestnut blight. On several occasions before this notable body I told of the successes and failures I had encountered, still believing that I was on the right road and insisting that an antigen would be absorbed in sufficient amount to stimulate immunity. Science has since vindicated that assertion and men are now injecting all sorts of chemicals, and even dyes to stain the grain of the wood.

I have been very cautious in the past and perhaps should be more so now, in view of the fact that only a comparatively few years have elapsed since I began my work on plants. Still, after having used vaccines on human beings and animals for twenty-one years, and observing that plant life reacts to an antigen in a similar manner, I am at least entitled to the same conclusions. This gives me an opportunity of knowing years in advance just what to expect.

While my work is still going on as an experiment I have no hesitancy in saying that I can and have put as much active immunity to the blight into the chestnut in five years as nature has been able to place in perhaps four or five thousand years by her usual method. However it is only fair to state that such results cannot be accomplished by mere oratory. Injections must be made and the antigen must go into the plants, not in single doses, if you please, but by the thousands.

In recent years there has been considerable discussion relative to the chestnut coming back. This simply means further delay. The chestnut will come back but not before from 25 to 150 years yet. There are few roots that will stand mutilation for that period, and the few plants that do survive will have taken the shrub form like the chinquapin, and the nuts will likely be as insignificant. I have plants from a tree that holds as much immunity in the natural way as any I know, being rated at 2X, and these plants have inherited an immunity equal to the parent, no more and no less. I have, however, a lot of seedlings from Paragon and Champion trees rated at from 6X to 7X. These seedlings may confidently be expected to perform as their parents and produce many plants of equal resistance.

I shall not discuss the antigen or its method of administration. That has been covered rather carefully in former papers. I do want to say a word, however, about root stock. In a blight region it is preferable to have chestnuts on their own roots. The nearest to own-rooted plants is a graft on their own seedlings. The Chinese and Japanese chestnut in my hands has made a very poor root stock for the American chestnut or its hybrids. The European chestnut is only fair, with the chinquapin somewhat better, but having the disadvantage of being troublesome to get from the seed. The American chestnut, or its American hybrids, is by far the best, providing we can get one with immunity. I think the Rochester will shortly fill this need.

The chestnut oak has made a rather interesting stock for a few varieties, notably a Chinese and 20 No. 3, a native American chestnut sent to me from Bloomsburg, Pa. I now have a few of these double grafted with other varieties.

I might say that I am no longer interested in any chestnut, no matter how resistant it may be, unless the nut is of large size and fine quality, because I can immunize a plant bearing a good size, fine quality chestnut much easier and in a shorter time than one can be developed through hybridization from an inferior nut. I am usually, like most folks, looking for the path of least resistance.

My work has been a good deal divided during the past few years because, while I started out with the chestnut alone, now I am carrying a dozen other fruits, nuts and berries.

In closing let me state that my principle of induced immunity is sound and the procedure feasible and practical.

The President: About the result of grafting the chestnut on a species of oak. How long have these scions been growing?

Dr. Zimmerman: About three years.

Mr. Hershey: How long?

Dr. Zimmerman: This is not the oak that I had reference to when you were up there. These are about three years old. I think they grow a little better than on the chestnut. Many of them died. I have another scheme now; that is grafting the scions as high as I can. Get them united and then bend them over and get them to root. Some are doing nicely, others have died.

Dr. Smith. I think you complimented us by thinking we could follow you. Do you intend to vaccinate the chestnut and make it immune and then expect it to transmit that immunity in its seed? Have you checked up in the second generation?

Dr. Zimmerman: I haven't had time yet.

Dr. Smith: Thus far you have established immunity in the living tree?

Dr. Zimmerman: Yes, and I have a bunch of seedlings now from nuts from immunized trees that I planted last spring. I have 200 of those. I expect them to inherit immunization from their parents.

Dr. Smith: We vaccinate each generation of youngsters.

Dr. Zimmerman: I was speaking of the experiments with guinea pigs.

Dr. Smith: Isn't smallpox vaccination against your theory?

Dr. Zimmerman: I don't think so. They are doing it with other things. I found a human being giving the reaction for typhoid for seventeen years after he had been immunized.

Dr. Smith: Have you any evidence for or against the decline of immunity in the tree?

Dr. Zimmerman: I think it will decline.

Dr. Smith: Then we have got to keep on immunizing like spraying. I didn't mean necessarily annually. I mean perhaps it is not a permanent achievement.

Dr. Zimmerman: I imagine that the tree will be sufficiently attacked by blight to keep the immunity up. It is wise to have it attacked once in a while.

Mr. Hershey: Isn't this only carried on until you get natural resistance?

Dr. Zimmerman: I know that it will be a long time before I can have chestnut trees to produce like Mr. Harrington's. But I am going ahead. I can't wait 17 years. All I need is some time and I will produce chestnuts of the finest varieties, as Mr. Harrington has.

Dr. Smith: How long will it take?

Dr. Zimmerman: They will hold their immunity as well as the Chinese. The ones I have are worth planting right now. I have trees that are standing up better than any Chinese chestnuts are. It takes a long time before the immunizing principle is so disseminated that every part of the tree will have an equal resistance. I can easily see that by cutting off a scion and grafting it I may get hold of one that has not had its immunization distributed as it should be.

Dr. Smith: A fairly ignorant man can take machinery and spray an orchard. Can he do the same with immunizing?

Dr. Zimmerman: No sir, he can not.

Dr. Smith: Perhaps I should not have used the word ignorant. A farm hand can spray and make a pretty good crop of apples.

Dr. Zimmerman: No, he can't do it. It hasn't been easy. I have run into all kinds of obstacles. As soon as I injure the stock a little bit the blight takes it. As soon as I can raise them on their own roots it will be all right. That will come.

Dr. Smith: Have you seen chestnut grafts root as the apple does?

Dr. Zimmerman: Yes, right below the surface. A couple of them were that long. They will send out roots. Then I have noticed on some, that at the place where I grafted the callus got quite large. It got too dry and died off. I have never rooted American chestnut cuttings. I have rooted some Chinese chestnuts.

The President: Some of the Chinese chestnuts root quite readily from those small shoots that come up from the ground. I conducted a little experiment in trying to propagate the Chinese chestnuts by cuttings. I made 144 cuttings. They all dutifully and beautifully died. I don't mean to say that the Chinese chestnut cannot be rooted by cuttings.

Dr. Zimmerman: I noticed one chestnut that was toppling over and the leaves were withering. The rats had taken it off just below the ground. I couldn't find a root anywhere, but it was callused. I cut it back and planted it again. It must have roots now for it is still green. Otherwise it wouldn't live this long.

The President: Your experiments are of very great interest. If you are successful you will deserve the gratitude of this and future generations.

Mr. Harrington: Do you remember when we were down at the Riehl nursery that we ran into a chestnut that produces 7 to 9 in a burr?

The President: I remember one tree that had a great many nuts.

Mr. Harrington: I had one with 7 nuts and they said there were some with 9. Was that the one named Gibbons?

Dr. Colby: That has three nuts to the burr.

Dr. Deming: Dr. Colby, there have been two instances of blight infection in Illinois. Could you tell us how the eradication was done?

Dr. Colby: In each case the tree was burned and the disease entirely eradicated by fire on the spot.

The President: Dr. Colby has a paper from Mr. Littlepage on the plant patent law.