Evidence that Austropuccinia psidii may complete its sexual life cycle on Myrtaceae

The rust fungus Austropuccinia psidii has spread globally and naturalized in areas with naïve species of Myrtaceae. Previous studies have revealed multiple strains of A. psidii within South America and two strains outside of its native range. The rust spreads by windborne mitotic urediniospores, which are the dominant spore stage. Teliospores and basidiospores of A. psidii are also formed; however, the biological role of these stages in the life cycle is unknown. Experiments presented here tested whether basidiospores of A. psidii could infect Syzygium jambos. The sori produced by infection with basidiospores were screened with five microsatellite markers to confirm whether they were a product of recombination. The findings showed that basidiospores of A. psidii could cause infection on species of Myrtaceae and the resulting sori were a product of recombination. This has important implications for programmes that breed for resistance to this aggressive pathogen in commercial eucalypt forestry.