Results of a Chinese Chestnut Rootstock Experiment
Reading edition
J. W. McKAY[4]
Introduction
The propagation of chestnut species by budding or grafting has been performed by different workers with varying degrees of success. Many have found that grafted trees could be produced and grown successfully but that graft union troubles developed in a certain percentage of the trees either soon after grafting or a few years later. The variety "Carr" is known to graft with difficulty in certain localities and to give a high percentage of poor unions both at the time of grafting and after a few years of growth. The question of relationship of scion and stock has been considered by many workers to have an important bearing on the success of grafting operations but no critical work has been done to determine this point. Some investigators hold that scions of one species may be grafted upon stock of another species without harmful effects. The results of the budding experiment with Chinese chestnut reported in this paper are the first of a series of tests designed to contribute needed information about stock-scion relationship in chestnuts.
Description and Results
The five seedling Chinese chestnut trees used in the experiment were selected because of their heavy-bearing tendency and because of the excellent keeping quality of the nuts. Two of the trees bear nuts of large size while the other three bear nuts of medium to small size. Seeds from the five trees were planted before the use of the seedlings as stocks in the budding experiment was planned, and since the seedlings from each tree were planted together replication of the experiment was not possible. However, the stock was grown in thoroughly mixed soil in a coldframe and differences in performance of seedlings could hardly be attributed to soil heterogeneity.
Buds from the five parent trees were placed on the five lots of their own seedlings in all combinations of budwood and stock. The work was done during the first week of September when the bark of both budwood and stock was slipping yet growth had slowed down to some extent. Buds were placed about two inches below soil level on the one-year-old seedlings and the soil pulled back to cover the buds. Budding was done by means of the familiar shield or T-bud method and rubber budding strips were used as a wrap. Budwood was shipped from Albany, Ga., to Beltsville, Md., and was damaged somewhat by high temperature in transit, a factor which may be partially responsible for the overall low percentage of buds that grew.
In referring to the results presented in table I, it will be noted that considerable variation occurred in the performance of the five lots of seedlings as stock, as well as in the take of buds from the five parent trees. The totals in the last column on the right are all equivalent to percentage since 100 buds were placed on each lot of seedlings. In like manner, the totals in the bottom line are all equivalent to percentages since 100 buds of each parent tree were used.
Seedlings of stock D were decidedly inferior to seedlings of stock C in take of buds, and both of these lots of seedlings originated from large nuts. Also, scion e gave a significantly lower take of buds on all lots of seedlings than scions c or d. The scion e tree produces small nuts whereas the scion c and d trees produce large nuts. Scions a and b are intermediate in take of buds, and the source trees both produce small nuts.
Discussion
At least one significant interpretation may be made from the results of this experiment, that may partially explain the difficulties encountered heretofore in propagating chestnuts. Using the take of buds as a criterion it can be stated that in this experiment the five lots of seedlings from known parents differed in their performance as stocks. Moreover, the five parent trees used as a source of budwood differed among themselves in the capacity of their buds to grow when placed on comparable lots of stocks. If these results are correctly interpreted it is clear that both the stock and the scion may influence the success or failure of propagation technique. Doubtless both of these variables have operated together in the propagation of existing varieties and, as would be expected, the results have been unpredictable. It seems likely that the grafting and budding of chestnut varieties should be worked out in the future on the basis of using understocks derived from the seed of special trees or clones found to be suitable sources by tests for grafting performance.
It should be pointed out that the five trees used in this work originated from two lots of seed imported from neighboring localities in China and probably are closely related. The fact that significant differences were obtained in this material furnishes basis for the belief that great variability in the budding performance of the Chinese chestnut is to be encountered in the many introductions that have been made into this country.
Table I. Results of budding each of five Chinese chestnut clones on its own seedlings and on the seedlings of four other clones. The figure for each combination represents the number of buds that grew out of 20 buds placed.
SCION
abcdeTotals
SA4645019
TB3284017
OC0389525
CD123118
KE2279222
TOTALS10153028891
Discussion After Dr. McKay's Paper
Dr. MacDaniels: "A good scion on chestnut is one problem which we have not solved."
Dr. Smith: "I find both Carr and Hobson difficult to graft and have discontinued them."
Dr. Crane: "In California and Oregon they are having quite a lot of difficulty with graft union failure with Persian walnuts. They have used the Northern California black or Hinds walnut as root stocks. Now they find that in some cases the union fails and results in what is known as the black line disease. At the present time this trouble is the most important cause of the loss of their trees."
Dr. Smith: "Zimmerman is a good bearing variety with a good nut. I find that soil makes some difference with this variety."