Pollen-parent affects fruit, nut and kernel development of Macadamia

The genotype of the pollen that fertilizes the ovule is known to affect the characteristics of fruits and nuts for many species, a phenomenom known as the xenia effect. Cross-pollination increases fruit set, nut mass, kernel mass and kernel recovery of macadamia nuts at maturity when compared with self-pollination. However there is limited information on the xenic effects of different macadamia cultivars used as cross pollen-parents on the fruit components and fruit development. The aim of this study was to clarify in what nut components and at what developmental stages xenic effects occurred. Two large-seeded macadamia cultivars, 'HAES 246' and 'HV A16', were used as maternal trees and pollen-parents were 'HAES 246', 'HV A16' and 'HAES 814', a small-seeded cultivar. Pollen-parents affected the mass of both the syngamous tissue of the kernel (embryo) and the tissues of maternal origin; i.e. the husk (pericarp) and shell (testa). Xenic effects were detected in the endosperm 6 weeks after pollination and in fruit, nut and kernel size and mass from 10 weeks after pollination until maturity. Nut mass, kernel mass and kernel recovery of macadamia were increased significantly by a different pollen-parent. The HV A16 pollen on HAES 246 flowers produced an increase of 11% nut mass compared with HV 814 pollen on HAES 246 flowers. This would increase the gross margin of a farm producing 4.5 t/ha of nuts by $2574/ha at typical 2018 prices. Macadamia growers and the macadamia industry would benefit from identification and use of the most beneficial cross-pollen sources available.