NORTHEASTERN FOREST EXPERIMENT STATION 

Upper Darby , Pennsylvania 

No. 74 

Testing American Chestnuts 

For Blight Resistance 

It has now been over half a century since chestnut 

blight, caused by the fungus Endothia parasitica (~urr.) A. 

& A., was introduced into America fromthe Orient. In that 

time the blight has spread relentlessly and has destroyed 

all of our comrnercial~stands of this once most valuable 

hardwood species of the East, 

A great many people are interested in seeing the 

American chestnut (~astanea dentata L. ) appear again as a 

regular member of our forest communities. Over 600 people 

in-36 different states have written to us, in response to a 

brief magazine article,l to tell us of living American 

chestnut trees. The locations of these trees, large and . 

small, are shown in Figure 1. 

Before receiving these recent communications we knew 

of only 57 large surviving chestnut trees. Now we know of 

many more. It is our hope that a,mong them may be a tree that 

hasn't simply escaped the blight, but has a high degree of 

disease resistance. Such a tree, if its progeny are also resistant to the disease, could provide a means by which American chestnut could be helped to grow in our forests again. 

Those large trees that have remained free of the 

blight in areas in which the disease is well established 

have the strongest possibility of possessing disease resistance. They have been exposed to infection for years, so 

their escape from the disease must be due either to the 

failure of the fungus to reach them under conditions favorable to infection or to disease resistance. 'de hope to debrahame, Arthur. Know Any Old Chestnuts? Outdoor 

Life, March 1957, p. 21. 
termine which of these possibilities is responsible for 

their survival. 

One way to test blight resistance is to artificially 

inoculate existing chestnut trees with the blight fungus. 

Some trees have been tested in this manner by a trained 

technician. Such work is slow, and our limited staff has 

been able to test only a few trees each year. Another method 

is to obtain scionwood from trees suspected of being blight 

resistant and graft them on small seedlings in areas where 

we know the blight is present. Resistant trees will live, 

others will die after sufficient exposure to the disease. 

0 

TREES 

TREES 

8 

3 

INCHES D.B.H. 

TO 7 INCHES D.B.H. 

AND LARGER 77 

u i\ v 

Figure 1.--Location of large Anierican chestnut trees as reported in the spring of 1957. The dotted line indicates 

the botanical range of American chestnut. 

During the past 4 years we have obtained scionwood 

from large chestnut trees that have survived the blight so 

far. Someofthis scionwoodhasbeenusedlocally. The 

rest has been sent to cooperators in 28 states who have 

grafted the material on seedlings in their localities. In 

this way we can be relatively sure that the grafted trees 

that survive i n a l l these different places, ?ram scionwood 

from a single source, have an excellent chance of being 
blight resistant. When these trees are much older our technicians can then subject them to artificial inoculations as 

final proof. 

Ue hope that all who have reported the occurrence of 

American chestnuts will keep the trees under observation. 

Periodic reports on their condition would be welcome. We 

also wish to learn of the locations of still other large 

American chestnuts. 

Those who wish to propagate their chestnut trees and 

test them can take scionwood from the tree and graft it onto 

other chestnut root stock. Detailed instructions on methods 

of making grafts may be obtained by writing to the U. S. 

Department of Agriculture, Washington 25, D. C. 

We are now compiling information gleaned from the 

letters we have received. We plan to extend our testing of 

American chestnut and will contact those who have reported 

trees that have the strongest probability of possessing disease resistance. By obtaining scionwood from such trees for 

propagation and testing in various localities we hope to determine if America possesses a blight-resistant native 

chestnut. 

--JESSE D. DILLER 

Forest Pathologist 

Virginia Pine-Hardwood Research Center 

Northeastern Forest Ekperiment Station 

Agriculture-Forest Service-Upper Darby, Pa.