Cross – Pollination Benefits in Macadamias | Philip Lee, CompleteLee Nuts Consulting
In collaboration with RedSun Hortitech
It has been known for some time that cross-pollination in macadamias improves nut set and nut size, thereby improving both yield and quality compared with nut production arising from self-pollination. Only recently, however, have research results started to quantify the magnitude of these improvements.
According to Howlett et al (2019) the 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.
Using caged and bagged racemes on three cultivars, Howlett et al (2019) 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). Their 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.
The amount by which yield can be increased by cross-pollination is illustrated by the unique and ground breaking research reported on by Professor Wallace of Griffith University, Australia. This work was carried out in two blocks of 48 rows each of cultivar 816 next to cultivar Daddow. The research team of ten people hand cross-pollinated some 40 000 racemes on ten trees in the middle of each block and ten trees at the edges of the blocks where a row of 816 was next to a row of Daddow.
By ensuring an abundance of cross-pollen in this way, yield of 816 trees hand pollinated with Daddow pollen increased from 1,3 tons NIS per hectare in the control trees (ten trees not hand pollinated) in the centre of the block to 2,5 tons NIS/ha. At the edge of the block yield of 816 increased from 2,1 tons NIS/ha to 2,7 tons NIS/ha. For Daddow the yield increase was from 2,8 tons NIS/ha to 3,9 tons NIS/ha in the centre row when hand pollinated with 816 pollen and from 3,1 tons NIS/ha to 4 tons NIS/ha in the edge row.
These results show that there were higher yields at block edges than in the centre of the blocks when trees are open pollinated, 0,8 tons DIS/ha in the case of 816 and 0,3 tons NIS/ha in the case of Daddow. On average the yield benefit from hand cross pollination in this research project was about one ton of NIS per hectare. It is particularly good to know that this is the potential yield improvement when flowers of one cultivar are saturated with pollen from another cultivar.
While nobody is suggesting that we should all go out and hand pollinate our trees to improve yield, this research has shown that we get at least 0,5 tons NIS in open pollinated trees when we have one row of one cultivar right next to a row of another cultivar. It is indeed worthwhile, and certainly practical, to plant two cultivars together in every block of macadamias, either one row of cultivar “A” alternating with one row of cultivar “B,” or two rows alternating to ensure that there is always a different cultivar in the next row.
More research on this subject is necessary to provide details about which cultivars work best together. But until this knowledge is available, all of the cross-pollination research done to date seems to indicate that there is always better nut set, nut size and therefore better yield and quality (bigger nuts have higher kernel recoveries) when two cultivars are planted together in a block to optimise cross-pollination.
Of course, it is essential to remember that cross-pollination will not happen unless we have bees and other vectors in orchards at flowering time, their work illustrated in Figure 1.
Figure 1. Nectar foraging honey bee having collected fluorescent powder across various parts of its body. Note the wing contacting the stigmatic region of a flower (photograph by Brian Cutting, Plant & Food Research). From Howlett et al (2017).
Pollination in macadamias – the latest research (2022). Australian Macadamia Society Podcast with Helen Wallace, Professor of Agricultural Ecology, Griffith University, Queensland, Australia.
Howlett et al, 2019. Cross-pollination enhances macadamia yields, even with branch level resource limitation. HortScience 54(4): 609-615.
Howlett B, Goodwin M, Read S, Evans L, Cutting B, Cross S, Pattemore D. January 2017. Optimising pollination of macadamia and avocado in Australia. A Plant & Food Research report prepared for: HIA Limited. Client project no. MT13060. PFR Milestone No. 58647 -M190. Contract No. 31007. Job code: P/414048/01. PFR SPTS No. 14126.