Stripe rust

Wheat stripe rust (Puccinia striiformis f. sp. tritici (Pst)) is listed as a bioterrorism threat to U.S. agriculture in the Bioterrorism Preparedness and Response Act of 2002 and was even developed, along with wheat leaf rust, by the USSR as a bio-warfare weapon (Bruce, Fink, & Lander, 2003). Wheat stripe rust is an important disease in all wheat growing regions of temperate-cold climates. It has been reported in over 60 countries (Chen, 2005) and is the second most important disease of wheat in Australia, causing an estimated $127 million in losses annually. Barley grass stripe rust (Psp-h), Cocksfoot stripe rust (Psd) and Kentucky Bluegrass Stripe Rust (Psp) are also present in Australia.

Variation in Pst in Australia has been largely observed in rust surveys based on host disease response with limited molecular studies. Simple Sequence Repeats (SSRs), also known as microsatellites, have shown some potential to reveal more information than other molecular markers in studies of Pst (Keiper et al., 2003, Spackman et al. 2010, Zhan et al. 2012). The range of SSR markers described to date ( Enjalbert et al., 2002, Bahri et al., 2009, Chen et al., 2009) have been of some value in illustrating contrasts between geographically separated Pst populations. However there is a need to develop a greater range of polymorphic SSRs that enable an expansion in studies between and within the variants of P. striiformis, including formae specilaes and pathotypes. The recent publication of the Pst genome (Cantu et al., 2011) provides an opportunity to develop an expanded range of SSR markers and to screen these on Australian isolates of P. striiformis. The development of a new suite of SSRs would have the potential to reveal insights into the evolutionary history of Pst within Australia as well as the mechanisms underlying pathogenic variability detected in the Pst population.

What is the biosecurity problem?

Rapid identification of unknown Puccinia striiformis. The known incursion events in Australia, and worldwide, demonstrate the ease with which pathogens, and new pathotypes, can be introduced into agroecosystems. Even with improved quarantine and biosecurity measures there is still the risk that further incursions may occur. With host boundaries between formae speciales of Puccinia striiformis being somewhat blurred and Barley Stripe Rust being considered a high risk pathogen to Australia (Spackman et al. 2010), a molecular based identification protocol would be very valuable.

The outputs of this project are to:

• Develop a diagnostic protocol for the rapid identification of potential foreign rust pathogens.
• Conduct a comprehensive analysis of molecular features of the Pst population in Australia.
• Assess the relationship between Pst and wild barley grass species. Wild barley grass identified as an ancillary host to Pst as well as the principal host of Psp-h .