Abstract Detail

Recent Topics Posters

Sandhu , Karanjeet Singh [1], Robert, Park F. [1].

Genetic diversity in Puccinia psidii and its pathogenicity to native Myrtaceae in Australia.

In Australia, myrtle rust was first detected in April 2010 from infected leaves of Agonis flexuosa, Callistemon viminalis and Syncarpia glomulifera. While originally described as Uredo rangelii, subsequent studies indicated that it was a member of the Puccinia psidii sensu lato complex. To differentiate it from eucalyptus/guava rust caused by P. psidii sensu lato, the disease was named myrtle rust based on the name Myrtus communis the original host of U. rangelii.  
The presence of vast numbers of potentially vulnerable native species of Myrtaceae and a lack of understanding of genetic variability in P. psidii in Australia led to this study, which included the collection and preservation of single pustule increased isolates of P. psidii, the establishment of protocols for germplasm screening, development of a scale to characterise host response, large scale phenotyping of Eucalyptus and non-Eucalyptus species, identification of potential differentials for surveying pathogenicity of P. psidii, and the development of microsatellite markers to assess genetic variability among Australian isolates of P. psidii. 
More than 20 rust isolates collected from diverse locations within Australia were increased from single pustules and preserved in liquid nitrogen at the Plant Breeding Institute. An isolate with accession number 115012, collected originally from A. flexuosa, was used as a standard culture for DNA extraction and for all germplasm testing. P. psidii was found to infect only young foliage, and Syzygium jambos was used as the susceptible control and for increasing rust inoculum. Successful infections were achieved with urediniospores inoculations followed by incubation at 20°C plus >95% RH for 24 hrs and at a post incubation temperature of 22 ± 2^oC. Thousands of myrtaceous plants raised from the seed lots of 69 Eucalyptus species, 10 hybrids of Eucalyptus and 110 non-Eucalyptus species were screened for resistance. Out of 69 Eucalyptus species tested, 52 showed a varied response against P. psidii whereas Eucalyptus cladocalyx was highly resistant. Age specific and all stage resistance was observed in E. globulus and E. grandis plants when tested at different growth stages. A majority of the non-Eucalyptus species was susceptible. Whereas some Callistemons, Leptospermums and Melaleucas showed a level of resistance against P. psidii, all guava cultivars tested were highly resistant. Individual genotypes of E. globulus and E. grandis showing resistant to susceptible infection types were identified as potential differentials for myrtle rust pathogenicity survey. Further work is required to establish a full set of differentials.  
Seventeen isolates of P. psidii from Australia, Brazil and Hawaii were selected to study the genetic diversity. Genotyping revealed three alleles among the isolates: one for Australian isolates and an isolate from Hawaii, second and third for two Brazilian isolates respectively. Markers revealed that all Australian isolates were genetically similar to the one from Hawaii. No genetic diversity was observed among the Australian isolates, supporting the hypothesis that only one genotype of P. psidii was introduced into Australia, potentially from Hawaii. Further SSRs were highly specific to P. psidii and can be confidently used as new tools to monitor the evolution of P. psidii in Australia and elsewhere.  

1 - The University of Sydney, Faculty of Agriculture and Environment, Plant Breeding Institute, 107 Cobbitty Rd. Cobbitty, Sydney, NSW, 2570, Australia

Keywords:
Myrtle rust
Disease Resistance
Puccinia psidii
SSRs
genetic diversity.

Presentation Type: Recent Topics Poster
Session: P
Location: Hall D/The Shaw Conference Centre
Date: Monday, July 27th, 2015
Time: 5:30 PM
Number: PRT021
Abstract ID:1805
Candidate for Awards:None