MOLECULAR DIFFERENTIATION WITHIN AND BETWEEN EUCALYPTUS-RISDONII, EUCALYPTUS-AMYGDALINA AND THEIR HYBRIDS USING RAPD MARKERS

Random amplified polymorphic DNA (RAPD) studies of a natural hybrid sw arm between Eucalyptus amygdalina Labill. and E. risdonii Hook.f. and nearby allopatric stands revealed that, despite clear morphological di fferences, all bands were shared between species. However, frequency d ifferences revealed genetic divergence between species, populations wi thin species, and individuals within populations. Variation was greate st between individuals within populations and lowest between species. For both species, the direction of variation which distinguished the t wo populations was in a different direction to that which separated th e two species, suggesting population differences were not due to intro gression but were the result of genetic isolation and/or strong locali sed selection. Several morphologically typical individuals with interm ediate RAPD profiles were detected in the hybrid swarm and nearby allo patric samples of both species, suggesting that some cryptic introgres sion may be occurring. Controlled F-1 crosses generally had closer gen etic affinity to E. risdonii, raising the possibility that some parent s used may have been advanced generation hybrids. While natural hybrid s selected for their intermediate leaf phenotype were usually also int ermediate between the two species using RAPD markers, some deviated ma rkedly toward E. risdonii. The study suggests that morphological appea rance does not necessarily reflect genetic (RAPD) status and in some c ases detectable RAPD differences between spatially close populations o f the same species may be as great or greater than the differences bet ween species.