Reprint from CMS 1972

In 1970, James, Makaimoku and Price reported the results of a study on carbohydrate buildup in girdled wood of Macadamia trees. In their study, carbohydrate assays from girdled specimens of the two species. Macadamia tetraphylla L. Johnson and M. integrifolia Maiden and Betche were made at regular intervals from early November to late January. The purpose of the experiment was to determine the time after girdling of maximum carbohydrate buildup. This would provide the basis to check for a correlation of the amount of carbohydrate and the degree of success in grafting. The purpose of the present experiment was to measure the carbohydrate levels in girdled wood during February and March and also to include the hybrid known as Beaumont. At the onset of the study all the nuts of the M. tetraphylla had dropped, the flower racemes were in tight buds, and a light flush was in progress with only scattered new growth visible. The M. integrifolia was not flushing, approximately 3/4 of its nuts had fallen and no flower buds were present. The Beaumont was flushing lightly, still had many nuts and no flower buds.

Procedure _ Branches were girdled on the same two trees that were used in the 1970 experiment of James, Makaimoku, and Price. The Beaumont tree selected is adjacent to the M. tetraphylla and is approximately the same height. The size of the branch, which was girdled, and its location on the tree was similar in each of the three trees. The carbohydrate extraction procedure followed in this study closely parallels the method used by James, Makaimoku and Price (1970) and Makaimoku (1971).

Results _The carbohydrate buildup in both the girdled M. tetraphylla and M. integrifolia was found to differ from the buildup recorded in November 1970 by James, Makaimoku and Price. It can be conjectured that the change in temperature, day length, vegetative condition of the tree or some other environmental or physiological variable or combination of variables is responsible for affecting the buildup pattern from one time of the year to the next. In M. tetraphylla the maximum carbohydrate buildup was on the 21st day with 62.3 mg of glucose per gm of tissue. In M. integrifolia the maximum was on the 29th day with 52.3 mg of glucose per gm of tissue. In the Beaumont the maximum was on the 36th day with 58.6 mg of glucose per gm of tissue. See Figure 1 for an extrapolation from the data. In November 1970 the maximum carbohydrate buildup for both species was 30 days after girdling. The mg of glucose per gm of tissue was 140 for M. integrifolia and 35 for M. tetraphylla.

About the only conclusion possible at the present time is that if grafting success is correlated with carbohydrate buildup, it should be done about a month after girdling. In ungirdled wood, approximately the same amount of carbohydrate was found M. tetraphylla in March 1972 as in November 1970. In ungirdled M. integrifolia, the amount of carbohydrate was significantly higher in March than in November. This might possibly be due to the very small crop of nuts the M. integrifolia had produced compared to the crop on the M. tetraphylla. Also the trees flush at different times. A phenological study of these trees is being made at the present time and the results may help to understand periodical changes in carbohydrates. Noel (1965, 1970) has related flushing to carbohydrate accumulation in the trees he investigated.