Cross-pollination Enhances Macadamia Yields, Even With Branch-level Resource Limitation

in HortScience

Macadamia is partially self-incompatible and cross-pollination is considered important to improve yields. However, questions remain regarding the importance of self- vs. cross-pollination, and subsequently whether managed pollinators are useful in commercial orchards. Pollinators play a key role in cross-pollination, but for self-pollination, the protandrous florets might also benefit from the movement of potentially more viable self-pollen among florets, racemes, and trees through pollinator movement. There is also a lack of information on pollination deficits throughout orchards and whether by increasing the intensity of cross-pollination, final nut yield is limited by within-tree resource allocation. Using caged and bagged racemes on three cultivars, we found strong evidence for self-pollination, but no evidence that hand moving self-pollen within racemes, between racemes, or between trees improved final nut set. In all cases, hand cross-pollinated racemes yielded significantly more nuts. Hand cross-pollinated racemes also produced significantly more developed nuts than open-pollinated racemes (all racemes were exposed to pollinators). However, by increasing the intensity of hand cross-pollination per tree, we showed that resource allocation probably overinflates these measures of pollination deficit in macadamia. Despite this, our findings point to an opportunity to increase yields through additional cross-pollination, as high-intensity hand cross-pollination of flowering racemes within trees still resulted in increased nut set. Although self-pollination can occur in macadamia, to optimize yield potential, strategies to maximize cross-pollination should be adopted.

Contributor Notes

This paper was presented as a part of the 2017 International Macadamia Research Symposium, 13–14 Sept. 2017, held at Big Island, HI.

We thank the Australian macadamia industry and the many macadamia growers for supporting this project. A special thanks to Clayton Mattiazi (Hinkler Park Plantation) for much assistance in trial work. Bryony Wilcox (University of New England) contributed significantly to key aspects of the research. Jenny Margetts, Robbie Commens, Jolyon Burnett, Chris Fuller, Chris Searle, and Claire Hall provided very useful feedback and recommendations. The students from Agrocampus OUEST, Rennes, France—Simon Cornut, Murielle Cuenin, Thomas Besnier, Philomene Brunelliere, and Victoria Potdevin—provided assistance with field work. Kelly Vorst-Parkes (Hort Innovation Australia), Robbie Commens, and Silvia Estrada-Flores provided invaluable support in promoting the research to growers. Anne Gunson and Jill Stanley provided editorial assistance. This research was conducted within the project MT13060 Optimizing pollination of macadamia & avocado in Australia (funded by Hort Innovation, the Australian Macadamia Society, and The New Zealand Institute for Plant & Food Research Limited). We also thank the anonymous reviewers of this manuscript and their useful comments.

Corresponding author. E-mail: brad.howlett@plantandfood.co.nz.

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    Mean final nut set per raceme (circle) and 95% confidence limits (error bars) of three macadamia cultivars a) 741, b) A268, and c) 816 following different pollination treatments: no hand-pollination open to pollinators (open), no hand-pollination caged and bagged (caged none), no pollination bagged (bagged none), within-raceme hand self-pollinated bagged (within raceme), between racemes within-tree hand self-pollinated bagged (between racemes), between-tree within-cultivar hand self-pollination bagged (within cultivar), between racemes of different cultivars hand cross-pollinated bagged (cross), and between racemes of different cultivars hand cross-pollinated caged and bagged (cross caged).

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    Mean final nut set per raceme for macadamia cultivars comparing hand cross-pollination (circles) and open pollination (squares) across five cultivar trials a) 741, b) Daddow, c) A268, d) A203, and e) 842, each using a different pollen donor cultivar. Error bars are 95% confidence intervals of the means.

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    Mean final nut set per raceme for two macadamia cultivars a) 842 and b) 741, each with varying hand cross-pollination intensity treatments (number of racemes crossed). Circles represent mean counts in hand-crossed racemes, squares are mean counts in untreated racemes on the same trees (‘741’ only). Error bars are 95% confidence intervals of the means.

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    Mean final nut set within the total area of cubic quadrats (0.75 m3) of macadamia cultivar 741, comparing control trees (no hand-pollination) (squares) with trees with 100 hand cross-pollinated racemes (circles), and showing the effect of the side of the tree. Error bars are 95% confidence intervals of the means.

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