Genetic diversity of the myrtle rust pathogen (Austropuccinia psidii) in the Americas and Hawaii: Global implications for invasive threat assessments

Abstract

Summary Since the myrtle rust pathogen (Austropuccinia psidii) was first reported (as Puccinia psidii) in Brazil on guava (Psidium guajava) in 1884, it has been found infecting diverse myrtaceous species. Because A. psidii has recently spread rapidly worldwide with an extensive host range, genetic and genotypic diversities were evaluated within and among A. psidii populations in its putative native range and other areas of myrtle rust emergence in the Americas and Hawaii. Microsatellite markers revealed several unique multilocus genotypes (MLGs), which grouped isolates into nine distinct genetic clusters [C1–C9 comprising C1: from diverse hosts from Costa Rica, Jamaica, Mexico, Puerto Rico, and USA‐Hawaii, and USA‐California; C2: from eucalypts (Eucalyptus spp.) in Brazil/Uruguay and rose apple (Syzygium jambos) in Brazil; C3: from eucalypts in Brazil; C4: from diverse hosts in USA‐Florida; C5: from Java plum (Syzygium cumini) in Brazil; C6: from guava and Brazilian guava (Psidium guineense) in Brazil; C7: from pitanga (Eugenia uniflora) in Brazil; C8: from allspice (Pimenta dioica) in Jamaica and sweet flower (Myrrhinium atropurpureum) in Uruguay; C9: from jabuticaba (Myrciaria cauliflora) in Brazil]. The C1 cluster, which included a single MLG infecting diverse host in many geographic regions, and the closely related C4 cluster are considered as a “Pandemic biotype,” associated with myrtle rust emergence in Central America, the Caribbean, USA‐Florida, USA‐Hawaii, Australia, China‐Hainan, New Caledonia, Indonesia and Colombia. Based on 19 bioclimatic variables and documented occurrences of A. psidii contrasted with reduced sets of specific genetic clusters (subnetworks, considered as biotypes), maximum entropy bioclimatic modelling was used to predict geographic locations with suitable climate for A. psidii which are at risk from invasion. The genetic diversity of A. psidii throughout the Americas and Hawaii demonstrates the importance of recognizing biotypes when assessing the invasive threats posed by A. psidii around the globe.

The risk to Myrtaceae of Austropuccinia psidii, myrtle rust, in Mexico

“…Our findings of suitable habitat for myrtle rust are consistent with previous work (Booth et al., ; Ross‐Davis et al., ; Stewart et al., ). Our model fits closely to the distribution of the pandemic biotype of myrtle rust in Hawaii (Anderson, ) and New Caledonia (Soewarto et al., ), both of which have extensive occurrence records.…”

“…This is particularly relevant if a new biotype is found, considering that different biotypes have different climatic preferences (Elith, Simpson, Hirsch, & Burgman, ). Nonetheless, we reiterate that our model projection is mostly consistent with previous work modelling the rusts’ global distribution (Booth et al., ; Stewart et al., ). The key departure from previous work is that our model projects greater suitable habitat in Chiapas, Tabasco and some regions in central Mexico (figure from Stewart et al., ) and lower suitability in the Yucatan Peninsula (Figure from Booth et al., ).…”

“…We undertook an exhaustive search to compile global occurrence data for A. psidii from a variety of sources. Specifically, we sought records from countries that have the same biotype of myrtle rust as Mexico, the pandemic biotype (Machado et al., ; Stewart et al., ), which include Australia, Costa Rica, Indonesia, Jamaica, Puerto Rico and Hawaii (USA). For records in Mexico, we searched data from GBIF, the Biological Collections of the National Autonomous University of Mexico (UNIBIO), the National Commission for the Knowledge and Use of Biodiversity (CONABIO), the Global Biodiversity Information (REMIB), literature and via personal communications (see acknowledgments).…”

“…The population structure and host specificity of the rust vary according to its distribution. While multiple biotypes have been identified via molecular analysis (Graça et al., ), the pandemic biotype occurs in Australia, Costa Rica, Indonesia, Jamaica, Mexico, New Caledonia, Puerto Rico, Hawaii and has recently been found in Colombia (Granados et al., ; Machado, Alfenas, Alfenas, Mohammed, & Glen, ; Stewart et al., ).…”

Symptom development and latent period of Austropuccinia psidii (myrtle rust) in relation to host species, temperature, and ontogenic resistance

“…Nine biotypes of A. psidii have been identified through molecular analysis, two of which occur outside the area of origin in Central and South America. These are the South African biotype, found only in South Africa, and the widespread pandemic biotype, which has been identified in Hawaii, Australia, New Zealand, Colombia, Southeast Asia, China, and Japan (Granados et al , ; Stewart et al , ; du Plessis et al , ). Information on the host range of each of the biotypes and the degree of host susceptibility is currently incomplete.…”