Effects of Cross-pollination and Flower Removal on Fruit Set in Macadamia

Abstract

Macadamia racemes were cross-pollinated and had flowers removed to determine whether manipulation of initial fruit set would affect final fruit set or yield. Examination of flowers collected 7 d after pollination indicated that the cross-pollination treatment generally induced a small (13-19%) but significant increase in the number of pollen grains per stigma. All flowers possessed some pollen grains, but in all cases cross-pollination approximately doubled the percentage of flowers with a pollen tube at the base of the style (42-68% of flowers on cross-pollinated racemes compared with 21-35% of flowers on control racemes). Fruit set after 14 d was always improved by cross-pollination, and this translated into increased final fruit numbers on two out of four occasions. In these two cases, kernel weights were increased by 24 and 31% in the cross-pollinated treatments. This indicates a possible xenic (paternal parent) effect in macadamia. Flower removal resulted in retention of a greater percentage of flowers as fruits, so that only severe reductions in flower number decreased final fruit numbers. Improved efficiency of cross-pollination in macadamia may increase both nut numbers and nut size.