Isozymic discrimination of tropical Australian populations of mesquite (Prosopis spp.): implications for biological control

Isozymic variation was investigated in five Australian populations and six reference collections of mesquite (Prosopis section Algarobia). Within nine enzyme systems, a total of 18 loci were examined in detail. 17 of which were polymorphic. Classification and ordination techniques revealed that two of the Australian populations were referable to P. pallida (syn. P. limensis) and another to a polyploid form of P. juliflora. Although the remaining two Australian populations were closely related, only one showed direct evidence of introgression of genes from P. pallida, and the existence of an additional, undetermined parent species was suggested. Owing to the apparent widespread distribution of P. pallida in northern Australia, it may be expedient to seek potential biological control agents from extra-Australian populations of either this or other species within series Pallidae. However, little is known regarding the general level of host specificity exhibited by the fauna which attacks species in section Algarobia. The overall degree of similarity of the taxa examined in this survey suggests that useful agents for Australian Prosopis might be obtained from the fauna associated with species from both series Pallidae and series Chilenses of section Algarobia.