Tracking down worldwide Puccinia psidii dispersal

Puccinia psidii causes rust disease on many host species in the Myrtaceae [1]. First reported in 1884 on guava in Southern Brazil [2], the rust has since been detected on several myrtaceous in South America, Central America, Caribbean, Mexico, USA: in Florida, California, and Hawaii. More recently, P. psidii was reported in Japan infecting M. polymorpha[3]. Of special note is that a rust was found infecting Myrtaceae species in Australia, where the fungus was reported as Uredo rangelii, based on the tonsure found on the urediniospores surface. However, DNA sequence data did not differentiate that rust from P. psidii[4], and the same tonsure patch, was also observed on rust urediniospores collected from several host species in Brazil [unpublished data].We have hypothesed that P. psidii was introduced into Hawaii through California by trade of rust infected myrtaceous plants, and that P. psidii populations from South America are distinct from the rust populations that became estabilished in California and Hawaii.