Benzyladenine delays immature fruit abscission but does not affect final fruit set or kernel size of Macadamia

Macadamia is a mass-flowering subtropical rainforest tree that is widely cultivated for its edible kernels. Macadamia flowers are borne on pendant racemes of 100 - 300 flowers but typically less than 2% of the flowers produce mature fruits and kernels. This study investigated the use of plant growth regulators to reduce abscission of flowers and immature fruit and to increase final fruit set of Macadamia. Preanthesis applications of the cytokinin, benzyladenine at 200 mg/L, increased initial fruit sets (2 weeks after anthesis) across four experiments from 8 - 17% (for control racemes) to 27 - 61% (for treated racemes). Post-anthesis applications of benzyladenine increased fruit retention up to 8 weeks after anthesis, but no treatment increased fruit retention beyond the final phase of immature fruit drop at 10 weeks post-anthesis. Benzyladenine delayed abscission of immature Macadamia fruit but it had no effect on final fruit set, nut-in-shell weight or kernel weight.