Impact of Irrigation and Artificial Pollination on Macadamia: Fruit Set and Yield

Severe flower and fruit abscission leading to low yields makes improving fruit set and increasing production critical challenges in Macadamia cultivation. Irrigation and artificial pollination during the flowering period significantly influence the fruiting and yield of macadamia. However, the synergistic effect of these two factors on macadamia production and yield remains unclear. This study investigated the effects of irrigation and artificial pollination on fruit set and yield using 11-year-old ‘A16’ Macadamia trees. Four treatments were applied: drought (DC), drought with artificial pollination (DC + AP), irrigation (I), and irrigation with artificial pollination (I + AP). Each treatment included three biological replicates, with a total of 12 trees. We assessed fruit set and yield, analyzing underlying mechanisms by evaluating changes in pollen viability, leaf morphology, inflorescence characteristics, and leaf/inflorescence physiology. Results revealed that DC + AP, I, and I + AP treatments exhibited significantly higher pollen viability and raceme length compared to DC. The I + AP treatment also resulted in the longest summer shoot internode length. Racemes were more sensitive to drought stress than leaves. Soluble protein and soluble sugar content in racemes were significantly higher in I + AP than in I and DC + AP, and lowest in DC. The DC treatment showed significantly higher superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), and malondialdehyde (MDA) contents compared to I and I + AP. Leaf physiological traits exhibited inconsistent changes across treatments. Both artificial pollination and irrigation significantly increased fruit set. Treatment efficacy ranked as follows: I + AP (102.00% increase) > DC + AP (56.00% increase) > I (14.00% increase) > DC. Consequently, the I + AP treatment achieved significantly higher yield, fruit numbers, and fruit diameters than the other treatments. In terms of yield, treatment efficacy ranked as follows: I + AP (77.72% increase) > DC + AP (41.14 increase) > I (27.54% increase) > DC. These findings provide a scientific basis for enhancing yield in high-yield Macadamia cultivation systems.