A total of 2400 hybrid nuts was harvested in the 1951 season and 1690 in 1952. This compares with the 1259 nuts reported for 1950. The increased production over past years can in part be ascribed to a concentration of the efforts on a fewer number of different crosses; while 103 were made in 1950, the total was 77 in 1951 and 80 in 1952. The pollinations followed the same general program in the two seasons, the emphasis being on the Chinese × (Japanese × American) hybrids. This is our most promising timber tree hybrid, and it seems worthwhile to test it on a somewhat larger scale under forest conditions. Therefore, some of the best early crosses have been repeated, new parent trees are being tried and selected hybrids intercrossed. Back-crosses to the native chestnut with the C×JA hybrids were made in an attempt to improve the form of the hybrid.
Another cross which has attained some importance in the last years is the hybrid between Japanese chestnut (forest type, from U.S.D.A.) and S-8, the latter being a hybrid between Japanese chestnut and C. pumila, the common chinquapin. This cross has a high degree of resistance and a sufficiently good form to make it a possible timber tree (Fig. 1). It is also a fairly good nut bearer with nuts which ripen early, perhaps due to the influence of the chinquapin parent (Fig. 2). Selected individuals of this hybrid were intercrossed, and some crossing with the native chestnut was done.
In the last two seasons the total harvest from some older Chinese trees (26 yrs.) was recorded. The best tree yielded 25.0 lbs. in 1951 and 28.2 lbs. in 1952; on other trees the yield varied between 15 to 22 lbs. The average size of the nuts varies considerably from year to year on the same tree. On one Japanese tree the average weight per nut was 5.6 g. in 1951 and 14.5 g. in 1952; on a Chinese tree the same values were 7.7 g. and 15.1 g. Other trees showed a 20-40 per cent increase in the average weight per nut in 1952 over 1951. This seems to indicate a marked influence of the climatic conditions during the latter part of the growing season on the weight of the nuts. A long-term study of this relationship might yield some interesting results.
[Illustration: Fig. 1. Hybrid of S-8 and Castanea crenata, U.S.D.A, forest type, 18 years old. About 35 ft. high. Good forest type and also good nut bearer. Blight resistant. Sleeping Giant Chestnut Plantation, Hamden, Conn. Photo by Louis Buhle, Brooklyn Botanic Garden. Sept. 26, 1952.]
[Illustration: Fig. 2. Fruiting branches and nuts of S-8 × crenata,
Sleeping Giant Chestnut Plantation. About 1/2 natural size. Photo by B.
W. McFarland, Conn. Agric. Expt. Sta. Sept. 8, 1952.]
Grafting
A considerable amount of grafting has been done since 1949 and the results have been good. Two year old Chinese transplants are usually used as rootstocks and all grafting is done in the field. The best results have been obtained where the rootstock plant was transplanted one year prior to the grafting. The simple splicegraft, or the bark or rind graft are used, depending on the size of the scion compared to that of the rootstock, the latter technique being used when the stock is considerably larger than the scion. There is some evidence of incompatibility; thus, scions from Chinese trees, or hybrids that show a dominance of Chinese characters, give a higher percentage of takes when grafted on Chinese rootstocks than scions from the native chestnut, or from hybrids between Japanese and native chestnut. Some indications of incompatibility between European and Chinese chestnut in grafts have also been encountered where scions received through the cooperation of Dr. C. Schad, Centre de Recherches agronomiques du Massif Central, France, and Count F. M. Knuth, Knuthenborg, Denmark, were used, but in some cases these grafts were successful. Topworking, using the veneer crown graft, has been quite successful as long as sufficient sap drawers are left on the stock (Fig. 3).
Inarching
The senior writer has already explained in detail (2) the simple method by which blighted chestnut trees can be restored to health and vigor by cutting out blighted areas in the bark, painting them over, and inarching or ingrafting one or more basal shoots into the healthy bark above the lesion. We do this work from mid-April to mid-May, and make a systematic canvas of all the trees in all our plantations, inarching all those where if is necessary or might be advantageous. Each operation requires only a few minutes. Last year we put in many hundreds of inarches, altogether, which later showed nearly 100% "take".
Owners of chestnut orchards should take advantage of this method of keeping valuable nut-bearing trees, although with cankered areas, in healthy, vigorous condition.