High outcrossing levels among global macadamia cultivars: implications for nut quality, orchard designs and pollinator management

Stephen Trueman, Mark G. Penter, Kátia Sampaio Malagodi-Braga, Joel Nichols, Anushika De Silva, Adalgisa Thayne Munhoz Ramos, Leonardo Massaharu Moriya, Steven Ogbourne, David Hawkes, Trent Peters, Naga Kasinadhuni, Shahla Hosseini Bai, Helen Wallace, Wiebke Kämper

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Abstract

Global fruit and nut yields are affected by shortfalls in pollinator populations, and pollen limitation is most prevalent among tropical, bee-pollinated and self-incompatible plants. Macadamia is a subtropical, bee-pollinated crop in which some cultivars have been found to be highly outcrossing. We aimed to determine the extent of outcrossing and its effects on nut quality across a wide range of international macadamia cultivars in three countries. We sampled fruit from 19 macadamia cultivars across 23 sites in Australia, Brazil and South Africa. We used genotype-by-sequencing and MassARRAY methods to assign paternity to individual fruit and we assessed pollen-parent effects on nut quality. Macadamia was highly outcrossing, producing 80–100% of fruit by cross-pollination, at 17 of the 23 sites. Mixed mating (41–72% outcrossing) was identified at five sites, and low outcrossing (10%) was identified in one cultivar at one site where it was isolated from other flowering macadamia trees. Outcrossed fruit often had significantly better quality than selfed fruit, with 1.61–3.39 g higher nut-in-shell mass, 0.53–1.55 g higher kernel mass, 3.3–6.4% higher kernel recovery, and 3.0–3.5% higher oil concentration. The differences in kernel recovery equated to differences in value of USD 433–841 per ton of nut-in-shell at prices of USD 3000 per ton. In summary, macadamia cultivars were mostly highly outcrossing, and outcrossed nuts often had higher quality than selfed nuts. Growers should consider interplanting different cultivars more closely and distributing bee hives more widely to maximise cross-pollination, produce high yields, and optimise nut quality.
Original languageEnglish
Article number203
Number of pages14
JournalHorticulturae
Volume10
Issue number3
DOIs
Publication statusPublished - Mar 2024
Externally publishedYes

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