A fascinating feature of most cereal rust parasites is their ability to infect an alternate host plant, often totally unrelated to the one on which they are normally found. The rusts undergo sexual recombination on these hosts, resulting in new races. Fortunately these alternate hosts are rare or not present in Australia. The last Cereal Rust Corner described the role of a plant known as the Star of Bethlehem in the disease cycle of leaf rust of barley in South Australia.
Leaf rust is found in virtually all barley-growing regions of Australia. Although epidemics do occur, the occurrence of leaf rust and crop losses due to the disease have been sporadic.
Regular monitoring of the parasite over the past eight years has suggested a greater diversity of races in South Australia, possibly due to the occurrence of the Star of Bethlehem on the Yorke Peninsula in that State.
Of particular interest over this period of time was the detection and spread of the Franklin race, capable of attacking not only Franklin but also Tallon (both with gene Rphl2), as well as Grimmett and Shannon (both with gene Rph4). This race was first isolated from a barley crop in Tasmania in 1991, and since then has been isolated from that State in most years.
The same race was detected in South Australia, Victoria and southern NSW in 1993. A similar Franklin race was isolated from two samples collected in the Ravensthorpe region in Western Australia during 1997. It is difficult to make firm conclusions about the origin of this race in Western Australia, but detailed comparisons in the greenhouse have shown one difference between the WA isolates and those from eastern Australia.
We expect the Franklin race to spread to Queensland, where Tallon and Grimmett are widely grown. Queensland breeders and pathologists are aware of this, and are introducing several new sources of resistance into cultivars currently under development.