Myrtle rust - an ecological and commercial threat

Puccinia psidii has long been considered a significant threat to Australian plant industries and ecosystems. In 2010, P. psidii was detected for the first time in Australia on the central coast of New South Wales. The fungus has since spread rapidly and is now widespread on the east coast of Australia. Our studies aimed to determine the host range and impact of P.psidii on species of environmental and commercial significance. The host range of P.psidii has increased rapidly exceeding 150 species from 37 different genera in Queensland. Puccinia psidii has now been identified from a range of native forest ecosystems including coastal heath, coastal and river wetlands, sand island ecosystems, and littoral, montane, subtropical and tropical rainforests. The impact of P. psidii on individual trees and shrubs has ranged from minor leaf spots to dieback and reduced fecundity. Tree death as a result of repeated infection has also been recorded for some species, with regenerating seedlings becoming infected and killed by P.psidii. Puccinia psidii infection has been recorded on flower buds, flowers and fruits of 27 host species. To date P.psidii has been identified from 11 species of eucalypts in Queensland, occurring mainly on seedlings, generally at low severity levels. However, on mature E.curtisii and E.carnea trees significant infection levels have been observed with shoot and stem dieback and death of coppice. To date there have been no detection of P.psidii in plantation eucalypts in Queensland but our screening studies suggest the potential for P.psidii to detrimentally impact upon eucalypts in the nursery and in young plantations. However, estimations of the heritability of resistance suggest that efforts to enhance resistance through breeding have reasonable prospects for success