WWETAC Projects

Project Title: Genetic characterization of guava rust (Puccinia psidii): Evaluating pathways of spread and assessing future threats

Principal Investigator: Ned Klopfenstein, USDA Forest Service, Rocky Mountain Research Station (RMRS)


Collaborators: Acelino C. Alfenas, Rodrigo N. Graca, and Cristina P. Aun, Universidade Federal de Viçosa, Viçosa, MG, Brazil; Tobin L. Peever, Washington State University, Pullman, WA; Amy L. Ross-Davis, Western Forestry & Conservation Association and USDA FS, RMRS; Mee-Sook Kim, Kookmin University, Seoul, Korea; Phil G. Cannon, USDA Forest Service, Forest Health Protection, Vallejo, CA; Janice Uchida and Chris Y. Kadooka, University of Hawai‘i at Mänoa, Honolulu, HI; Robert D. Hauff, Hawai‘i Department of Land and Natural Resources, Honolulu, HI

Key Issues/Problems Addressed:
Puccinia psidii, the cause of a rust disease of multiple host species in the Myrtaceae family including guava, eucalyptus, rose apple, and ohia, was recently introduced to Hawaii where it infects an endemic tree species known as ohia (Metrosideros polymorpha), the dominant tree species in Hawaii’s remnant native forests. Despite potential threats to world-wide forest ecosystems and an expanding geographic range of P. psidii, little is known about the genetic structure of pathogen populations, migratory routes, and sources of introductions.

Setting and Approach:
Approximately 150 single-spore isolates of P. psidii, which were collected from diverse host species/locations in Brazil, were assessed at 10 microsatellite loci to determine the genetic diversity of pathogen populations. Additionally, 49 P. psidii isolates were collected from five host species across multiple Hawaiian Islands and assessed for genetic diversity.

Key Findings:

  • P. psidii studies in Brazil indicate that:  1) considerable genetic diversity is present, 2) species of hosts strongly influence population structure, and 3) distinct multi-locus genotypes are uniquely associated with specific hosts across diverse geographic locations.
  • All 49 rust isolates collected from five different hosts in Hawaii share a unique, multi-locus genotype indicating a recent introduction of a single rust genotype.
  • None of the rust genotypes in Brazil are known to occur in Hawaii suggesting that South America may not represent the immediate source of P. psidii that was introduced to Hawaii.


The wide host range of the P. psidii genotype found in Hawaii likely indicates a serious invasive pathogen risk for other global locations. Introduction of novel P. psidii genotypes to Hawaii represents an additional threat to native and exotic myrtaceous species because currently only a single P. psidii genotype has been found there.


Graça, R.N.; Alfenas, A.C.; Ross-Davis, A.L.; Klopfenstein, N.B.; Kim, M.-S.; Peever, T.L.; Cannon, P.G.;  Uchida, J.Y.; Kadooka, C.Y.; Hauff, R. D. 2011. Multilocus genotypes indicates differentiation between Puccinia psidii populations from South America and Hawaii. pp. 131-134 in: Fairweather, M.L.; Palacios, P., compilers, Proc. 58th Western International Forest Disease Work Conf. 4-8 Oct. 2010, Valemount, BC, Canada. US Forest Service, AZ Zone Forest Health, Flagstaff, AZ. (pdf, 1.5MB)

Hanna, J.W.; Graça, R.N.; Kim, M.-S.; Ross-Davis, A.L; Hauff, R.D.; Uchida, J.Y.; Kadooka, C.Y.; Rayamajhi, M.B.; Arguedas Gamboa, M.; Lodge, D.J.; Medel Ortiz, R.; Lopez Ramírez, A.; Cannon, P.G.; Alfenas, A.C.; Klopfenstein. N.B. 2012. A bioclimatic approach to predict global regions with suitable climate space for Puccina psidii. In: Proceedings of the 59th Western International Forest Disease Work Conference. 11-14 October 2011, Leavenworth, WA, USA. USDA Forest Service, Forest Health Protection, Region 5, Portland, OR. in press.

Klopfenstein, N.B. et al. 2011. Approaches to predicting current and future distributions of Puccinia psidii in South America under climate-change scenarios. pp. 450-454 in: Proceedings of the IUFRO working group 2.08.03 Improvement and Culture of Eucalypts. 14-18 November, Porto Seguro, Bahia, Brazil. Escola Superior de Agricultura “Luis de Queiroz” (invited).

WWETAC Project ID:  FY10TS82

guava rust

Figure 1. Hosts of guava rust caused by Puccinia psidii. (A. Eugenia uniflora; B. Psidium guajava; C. Myrciaria cauliflora; D. Metrosideros polymorpha) (from Alfenas et al. 2009).