FRUIT-SET, ABSCISSION AND DRY-MATTER ACCUMULATION ON GIRDLED BRANCHESOF MACADAMIA

The patterns of fruit growth, abscission and dry matter accumulation w ere determined for ungirdled macadamia branches and compared with the patterns on girdled branches. The relationships between fruit set, fru it drop, and the number of available leaves were also assessed. Approx imately 50 leaves were required to support development of each fruit o n girdled branches, so that final fruit numbers on girdled branches we re higher or lower than on ungirdled controls, depending on leaf numbe r. High leaf numbers did not cause any increase in fruit size on girdl ed branches, but low leaf numbers resulted in fruit volumes up to 23% lower than the controls. The number of fruits set on ungirdled branche s was independent of the number of leaves on the branch. Defoliation o f ungirdled branches had no effect on the number of fruits set, with f ruit set on these branches apparently being supported almost entirely from carbohydrates obtained elsewhere in the tree. Three phases of fru it drop were observed, with maxima at 2, 6-7, and 10 weeks post-anthes is, separated by phases of relatively low fruit drop at 4 and 8 weeks post-anthesis. The maximum dry weight increase of the crop occurred be tween 10 and 20 weeks post-anthesis, when there was very little fruit drop. Therefore, although limited availability of assimilates may infl uence fruit retention in macadamia, there is no simple relationship be tween structural carbon demand and fruit drop.