Characteristics of flowering stems and raceme position in macadamia

Macadamia (Macadamia integrifolia Maiden and Betche, M. integrifolia × tetraphylla Johnson) flowers are borne on racemes that usually originate from axillary buds in response to cool conditions. In this report, we examine the relationship between stem characteristics and the number of racemes produced, to improve our understanding of the control of floral initiation and axillary bud release. Two macadamia trees of each of the cultivars ‘A4’, ‘660’, ‘695’, and ‘A38’ were pruned annually for 3 years and the relationships between stem length, stem age, the number of vegetative flushes, stem orientation, and the number of racemes produced were quantified in year 4 (2006). In addition, trees of cultivar ‘849’ were pruned in Autumn and early Summer, and the flowering characteristics of the post-pruning vegetative flushes were monitored the following Spring (2006). There were significant differences in the extent and location of racemes between cultivars. Racemes were produced preferentially on short stems that consisted of few vegetative flushes. In cultivar ‘A4’, 1-year-old stems were more likely to flower than 2-year-old stems; whereas, in cultivar ‘A38’, 2-year-old stems were more likely to produce racemes than 1-year-old stems. As stem orientation changed from horizontal to vertical, the likelihood of raceme production increased in cultivar ‘660’ stems consisting of one flush and in ‘695’ stems consisting of two flushes. Stem characteristics, particularly stem age and vigour, indicate the likelihood of flowering, but position within the canopy may be another important consideration. Canopy management practices that promote the production of short stems may increase whole-tree raceme production and, given the variation in the location of raceme production with cultivar, canopy management practices specific to cultivar should be considered.