HYBRIDS AND OTHER NEW CHESTNUTS FOR BLIGHT DISTRICTS.
DR. WALTER VAN FLEET, WASHINGTON, D. C.
The sinister spread of chestnut blight, as the bark disease caused by the fungus Endothia parasitica is popularly called, within little more than 10 years, from its place of apparent origin near New York City into 13 states, practically reaching the eastern and northern limits of our native chestnut stands, and sparing in its course no individual trees exposed to infection, has about convinced even the most optimistic observers that without the intervention of natural checks the American chestnut as a forest asset will soon pass away. There is no present indication of diminution in the virulence of the fungus parasite and little reason to hope its progress as a timber destroyer can be stayed by any agency in the control of man. Already the losses, direct and indirect, occasioned by chestnut blight are computed as high as $50,000,000, about half of the estimated value of the entire stand.
With the very reasonable assumption that our native chestnut is doomed to virtual extinction it is well to consider in time if it can be replaced as a timber and nut-producing tree by other chestnut species or combinations of species less subject to injury by this disease-producing organism. The Endothia fungus, as a destructive parasite, is apparently confined to the chestnut, rarely if ever harmfully affecting genera even as closely allied as the oak (Quercus) or Castanopsis. Of the various species of chestnut or Castanea those native to Japan and Central China appear most resistant, probably having been for ages accustomed to the presence of the fungus, while the European chestnut, Castanea sativa, our native C. Americana, and our chinquapin, fall easy victims when exposed to infection. Of the Asiatic forms Castanea crenata of Japan and Eastern China and C. molissima of the interior are most promising in this respect, though the latter is still an almost unknown quantity as regards cultivation in this country.
Castanea crenata, commonly known as Japan chestnut, in its more typical forms is highly resistant, so seldom showing material injury that, for practical purposes, it may be regarded as immune. Japan chestnut seedlings raised from nuts grown in proximity to our native chestnut and exposed to the influence of its pollen are at times more seriously affected, but are rarely destroyed by the bark disease. The Japan chestnut is of comparatively low growth, of small value for timber purposes, but as a nut-producer is very fruitful and precocious, bearing great crops at an early age. The nuts are often very large but usually of poor quality. The species, however, proves quite plastic in the hands of the plant breeder, being readily modified in the directions most desired by the ordinary methods of cross-pollination and selection. It freely hybridizes with all other chestnut species and varieties that have been tried, and forms the basis of the most hopeful work in breeding for disease-resistance that has yet been attempted.
Castanea molissima is of much taller growth and bears nuts of moderate size, but of really good quality in the types that have reached this country. It can be infected by Endothia parasitica but the disease progresses slowly and in some instances results in little harm. The species has been so recently established in America that practically nothing is known of its breeding capabilities, but if its disease-resistance under our climatic conditions is assured it would appear most hopeful material for replacing our vanishing native species. Explorers report there is a still more promising chestnut in China, reaching nearly 100 feet in height under forest conditions, but it has not yet been secured for trial in this country.
Castania sativa, the commercial chestnut of Europe, in many varieties has long been cultivated in America and for nut production is without doubt the best of the well-known exotic species. It has no great timber value, however, and its disease-resistance, though higher than C. Americana, is scarcely great enough to warrant extended use as breeding material.
The native chinquapin, Castanea pumila, in its bush and tree forms remains as the only promising chestnut not found in the Orient. While readily inoculated by artificial means, the chinquapins, especially varieties of the northern bush forms, quite often escape natural infection, doubtless because of their small size, smooth bark, and less liability to insect attacks.
Chestnut breeding for nut improvement, chiefly by selection of native European and Japanese species, has been carried on in several diverse localities in the United States, with distinctly promising results but inter-pollinations have also been effected between most species and varieties, the outcome indicating that rapid improvement along the desired lines may be expected from crossing the really desirable types.
In 1903 and succeeding years the writer made many careful pollinations of the native chestnut and the bush chinquapin with European and Japanese chestnuts in many varieties. Some hundreds of seedlings resulted, mostly showing a high level of promise as judged by their initial thrift and vigor of growth, but the appearance in 1907 of the Endothia disease among the plantings soon put an end to the work with the native and European chestnuts, as, with scarcely an exception, they quickly became infected. The crosses of chinquapin and Japan chestnut, however, showed considerable resistance as a whole, and a number of individuals have resisted infection until the present time, though constantly exposed to the disease, both at their locality of origin in New Jersey and since at Arlington farm, to which they were transferred in the second and third years of growth. Others have been attacked in greater or less degree, but show great powers of recuperation, sending up suckers that often fruit well by the third year. The resistant varieties show great promise as nut producers, coming into bearing when three or four years old from seed and producing abundant crops of handsome nuts, of excellent quality, four to six times as large and heavy as those borne by the chinquapin parent, ripening in early September before chestnuts of any kind have appeared in the market. These nuts have thicker shells than other chestnuts, are much less subject to attacks of the chestnut weevil and preserve their fresh and inviting appearance longer when gathered. The flavor varies somewhat according to the particular pollen parent of the different varieties, but is always agreeable in the fresh state when the nuts are properly cured. When boiled or roasted they are particularly sweet and pleasant to the taste.
The trees are quite vigorous in growth, considering their rather dwarf type, reaching 10 or more feet in height at 6 to 8 years from the germination of the seeds and with scarcely an exception bear regular and increasing crops after the third year. Propagation of the most promising varieties has been effected by grafting and budding on Castanea molissima seedlings as resistant stocks, but it cannot be said that these processes, when performed under greenhouse conditions, give ideal unions. It is hoped to make fairly extensive trials of C. molissima and C. crenata as stocks for field grafting the coming season.
But the most encouraging feature of these chinquapin-crenata crosses is the excellence of their seedlings as grown from chance or self-pollinated nuts. Fifteen direct or second generation seedlings and one of the third generation have fruited to date. All have retained in growth and fruitage the characters of their immediate parent and it almost appears as if the good qualities of these hybrids may be perpetuated from seeds, thus dispensing in a great measure with vegetative propagation—always costly and uncertain with nut trees.
Several hundred of these seedlings are under observation and it scarcely appears too much to hope that they may inherit the disease-resisting character of their parents as well as other desirable qualities.
Selection work with a precocious strain of Japan chestnuts of apparently pure type has been continued through 4 generations of seedlings after an initial cross-pollination of two particularly desirable varieties had been made in 1903. These seedlings show greater range of variation than the hybrids with chinquapin, but all bear nuts of marketable value in 2 to 4 years from germination. None have been attacked by the Endothia fungus, though many have constantly been exposed to infection. Notwithstanding their extreme precocity trees of this Asiatic strain grow steadily and if thickly planted in favorable localities may in time produce timber of local value, but it is to the taller growing species of middle China that we must look for material to replace our vanishing native forest stands. The preservation in this country of the chestnut as a nut-bearing tree appears assured in view of the progress already made and it should not be too much to hope that resistant strains of the timber type may yet be developed by systematic breeding experiments.
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THE PRESIDENT: Inasmuch as the author of the paper is not present to answer questions, the only thing that may be done is to ask further contributions of knowledge in the same field. Has anyone any contribution to make?
MISS LOUISE LITTLEPAGE: I would like to ask how long the chestnut tree has been able to live with the blight?
DR. METCALF: Do you refer to the Asiatic ones or to the ones that grow here in America?
MISS LITTLEPAGE: The American.
DR. METCALF: It is almost impossible to answer that question because you have to define just what you mean by "living." If the chestnut tree is attacked first or early on the trunk, it is girdled and dies shortly, but if it is attacked first on the top there develop conditions like what is shown in this picture (showing photograph). I am not certain that you can see these bunches of suckers a little way up the tree. Now those trees will sometimes exist four or five years. I can say safely that I have seen trees last five years.
DR. MORRIS: I can add three years to that.
THE PRESIDENT: If there is no further discussion, we may adjourn.
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FRIDAY, SEPTEMBER 8TH, AT 8.15 P. M.
Meeting called to order by the President.
THE PRESIDENT: To my mind nut growing is part of a larger field, a field of conservation, one which is going to develop a whole new series of tree crops, of which the nuts are but a part.