CHARACTERISING MACADAMIA GERMPLASM WITH CODOMINANT RADIOLABELLED DNA AMPLIFICATION FINGERPRINTING (RAF) MARKERS

The cultivated subtropical nut crop macadamia is based on two Australian native species, Macadamia integrifolia and M. tetraphylla. The macadamia industry prefers M. integrifolia, although hybrid cultivars do occur. There are preliminary results to indicate that breeders may be able to exploit hybrid vigour, but to advance these studies, hybrid status must first be resolved. At present, species allocation is diagnosed on the basis of a few morphological traits, but this is inadequate to resolve proportional contributions of each species to each hybrid genotype. Neither can morphology be used to distinguish each cultivar or satisfactorily organise the complicated array of available cultivars. Such gaps in our knowledge may be filled by application of new DNA marker technologies. Radiolabelled DNA amplification fingerprinting (RAF) is a DNA marker technique recently applied to macadamia chromosome mapping. Here we demonstrate RAF to be a simple technique for identifying highly informative codominant markers in macadamia. We have discovered 19 new RAF codominant markers, which were used together with dominant markers to characterise 30 cultivars representative of the macadamia industry. Individual identity was assigned to each cultivar, and species proportions were calculated. Many cultivars contained a higher degree of M. tetraphylla than was previously thought. The markers were also used to assign cultivars to germplasm groups that reflected species status and breeding origins. Species composition was found to be a major determinant of group distinction. We now have a simple screening procedure for characterising macadamia germplasm.