DNA paternity testing indicates unexpectedly high levels of self-fertilisation in macadamia

Abstract

The recently domesticated nut crop macadamia is partially self-incompatible. Variation in the capacity for self-fertilisation is likely to have significant consequences, both for commercial nut production and the conservation of native populations. Molecular paternity testing using 11 microsatellite markers was conducted on open-pollinated seedling progeny of cultivar ‘741’, and mature kernel from eight different cultivars, seven of which have been used in previous self- and cross-pollination studies. The study was based in a varietal trial plot containing 40 different cultivars. Paternity was assigned to 92% of seedlings and 87% of kernel assessed. For four cultivars, selfing rates of 20–40% were detected. Estimates of relatedness between cultivars indicate a first-degree relationship between the two most widely grown cultivars in Australia, ‘741’ and ‘344’, at the level of full-sib or parent-offspring. Insight into the breeding system of macadamia is likely to have major implications for landscape and orchard-scale management. Our results point to significant differences in the capacity for self-fertilisation between cultivars and provide new molecular evidence of pollen flow under orchard conditions.