Relationships between kernel oil content, fruit removal force and abscission in macadamia

Delayed or extended fruit abscission in many cultivars of macadamia, Macada mia integrifolia (Proteaceae), necessitates multiple harvests from the orch ard floor. However, it is not known whether there is a link between fruit m aturation and timing of abscission. In this study, relationships between ke rnel oil content, nut size, removal force and abscission were investigated in 2 commercial orchards, one in Queensland (24 degrees S) and one in New S outh Wales (29 degrees S). Abscission lasted 6 months (March-September) at both sites due to differences in timing of abscission between cultivars and extended abscission within cultivars. Abscission was consistently associat ed with declines in fruit removal force, from more than 2 kgf in early Marc h towards 1 kgf at the peak of abscission. Later abscission in cvv. A16 and 246, compared with cvv. 344 and 741, was correlated with more gradual decl ines in removal force. Fruits containing small nuts and kernels tended to p ossess lower removal forces and these fruits were often heavily represented in the population of fruits that abscised earliest. There was little or no difference in kernel oil content between fruits of different removal force or between sample dates for any cultivar, either for samples taken from th e tree or from the orchard floor. Attainment of maximal oil content and ons et of fruit abscission are therefore independent processes in macadamia. If abscission can be accelerated, it may be possible to advance the harvest o f late-abscising cultivars such as A16 and 246 which retain mature nuts on the tree up to several months after maximal oil accumulation.