The influence of pollen-parent and carbohydrate availability on macadamia yield and nut size

Abstract

Cross-pollen parents can affect fruit set and yield, and can influence fruit and seed characteristics of many tree crops. Available carbohydrates also limit fruit set and yield, and tree carbohydrates can be manipulated by girdling trees and by defoliation. We investigated how different macadamia cross pollen-parents and the availability of carbohydrates interact to modify macadamia fruit set, kernel yield and kernel size. We manipulated tree carbohydrates by selecting different branch sizes and girdling branches on macadamia cultivar ‘HAES 246’ (‘246’) maternal trees. We applied pollens from two different commercial cultivars, ‘HV A16’ (‘A16’) and ‘HAES 814’ (‘814’) in two experiments. In Experiment 1, two branch sizes, 150 leaves and 500 leaves were girdled. In Experiment 2, three branch sizes, 150 leaves, 300 leaves and 500 leaves were both girdled and ungirdled. Final fruit set and kernel yield per branch were significantly higher on the girdled 500 leaf branches compared with the girdled 150 leaf branches in both experiments (P < 0.05). There was no pollen-parent effect on final fruit set or kernel yield per branch on girdled branches. Kernel mass was increased by the ‘A16’ pollen-parent in 4 out of 4 cases in experiment 1 and in 4 out of 6 cases in Experiment 2. Available resources also impacted on nut and kernel size. The ‘A16’ pollen-parent also increased kernel recovery significantly (P < 0.05) on some girdled and ungirdled branches. Carbohydrate supply and pollen-parents interact to determine final nut and kernel size and nut characteristics. Selecting suitable pollen-parents could improve macadamia profitability.