Pollination services in a macadamia cultivar depend on across-orchard transport of cross pollen

Abstract

Pollination services are critical in entomophilous crops. Relationships between pollinator visits and fruit set and mass are complex and optimal strategies to improve pollination are poorly defined. We often do not understand what proportions of the crop result from self- or cross-pollination, how cross-pollination affects crop quality and how far cross-pollen is transported. We quantified proportions of self- and cross-paternity in nuts of the partially self-incompatible macadamia cultivar 816 at increasing distances from cross-pollen sources. We estimated the distance of effective pollen movement, evaluated how pollination by different parents affected nut size and nutritional quality, and assessed whether distance from a cross-pollen source determined proportions of cross-pollinated nuts, nut size and number of nuts harvested. Almost all nuts resulted from cross-pollination, even at 184 m (23 rows) from a cross-pollen source. The cross-pollen cultivars in closest proximity were usually the pollen parents. Cross-pollination increased nut size and altered kernel nutritional quality. The number of harvested nuts decreased with increasing distance from a cross-pollen source in one orchard. Nut size was generally not affected by distance from a cross-pollen source. Synthesis and applications. Macadamia nut production resulted almost entirely from cross-pollination. Crop production was dependent on across-orchard transport of cross pollen, sometimes over at least 184 m. This shows the importance of pollen genotype, not just pollen quantity, in ensuring an effective pollination service. The number of harvested nuts decreased at 24 m from a cross-pollen source, suggesting that different cultivars should be inter-planted more closely in macadamia orchards. We need to better understand pollinator behaviour, including what genotype of pollen the different flower visitors carry, and how far and in what direction they transport pollen across orchards, to optimise crop yield and quality.