In 1934 we produced a cross of Chinese and American chestnut which proved to be unusual in several respects. The leaves are enormous—9 inches to 1 foot in length, and 4 or 5 inches in width. The hybrid is not particularly blight resistant but more so than its American parent. It died back from the blight about 1940 and the present tree has developed as a shoot from the old roots. The growth is rapid and vigorous. The flowers appear normal, but we have never been able to make a cross with its pollen, nor to effect fertilization of its pistillate flowers. It may be triploid, that is, with 3 sets of chromosomes instead of the normal double set, and this would account for its barrenness.
In the spring of 1952 some of the vigorous shoots of this tree were successfully grafted on shoots from an old stump of Chinese chestnut, using the veneer crown graft method. The scions had not been taken when dormant, but were transferred directly from the tree to the stock in late April. This grafting was done in order to impart greater resistance, if possible, to the CA hybrid by means of the roots of the Chinese stock.
3. Systemic Defect
Since the early 1930's we have seen occasional individuals with abnormal foliage—somewhat mottled, usually curled and often misshapen. Thinking that a virus might be the cause of this trouble the senior author tried grafting some of the shoots on to healthy stocks. The grafts were in no case successful because the scions were too weak. Finally he succeeded in grafting a branch from an affected tree on to a branch of a normal individual. The only result was an increased vigor of the healthy branch. This year he rubbed juices from leaves of such an abnormal individual on to wounded healthy leaves, without result. Moreover, such sick individuals, although growing for years close to healthy trees, have never communicated the malady to their neighbors. Growth is comparatively slow, and there is much dying back or dying out of the slender branchlets.
The evidence indicates that this is not a virus trouble, but a systemic defect, probably caused by chromosome aberration or gene abnormality. It is significant that this trouble occurs only in hybrids. Such trees never flower. We have known four such cases, two of which are now dead. Similar types appear in other species as inherited deviations from normal.
Insect Injuries
A heavy attack from the spring canker worms developed in 1951, but spraying with DDT on May 24th prevented serious damage. No outbreak of canker worms appeared in the spring of 1952. The Japanese beetle has been very little in evidence. The principal bad actors are the mites, Paratetranychus bicolor. Although barely visible to the naked eye, the effect they produce of whitening the leaves is conspicuous, especially on the Chinese chestnut and its hybrids. These insects overwinter in egg form on the surface of the bark. Last winter they were so numerous on some of the trees that the bark had taken on a red color—especially on smooth-barked trunks just below a branch. An application of "Scalecide" on April 21, while the trees were still dormant, followed by two heavy applications of "Aramite" (6-7 lbs. per acre) on June 13th and 27th, gave good control for the rest of the summer. Spraying with DDT for weevils was done on August 18th and September 3rd in 1952 with good results.
Cooperative Hybrid Chestnut Plantations
In 1947 the first hybrid chestnut plantation under forest conditions was made in cooperation with the U.S.D.A. Bureau of Plant Industry, Division of Forest Pathology. The plantations are made in order to test the hybrids under normal forest conditions and different climatic conditions. In general, each plantation consists of about 100 trees, 50 U.S.D.A. hybrids and 50 Connecticut hybrids. The trees are planted at a 10' by 10' spacing, and the overstory is girdled at the time of planting in order to give the plants better light conditions without causing an abrupt change in the microclimate of the forest floor—a method developed by Dr. J. D. Diller of the Division of Forest Pathology (1). Ten plantations at 9 locations have been established since 1947. These are listed below:
No. of Plots Location Year Established —————————————————————————————————- 1 Edward Childs Estate, Norfolk, Conn. 1947 1 Tennessee Valley Authority, Norris, Tenn. 1947 1 Table Rock State Park, Pickens, S.C. 1948 1 Antioch College, Yellow Springs, Ohio 1948 1 Upper Perkiomen Valley Park, Green Lane, Pa. 1949 1 So. Ill. Univ. Fish & Wildlife Service, Cartersville, Ill. 1949 1 Russ State Forest, Decatur, Mich. 1951 2 Nathan Hale State Forest, Coventry, Conn. 1951 1 Ouichata Nat'l. Forest, Hot Springs, Ark. 1952 —————————————————————————————————-