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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