IN REVIEW: cereal rusts in 2001 season
GroundCover™ Issue: 40
with Dr Robert F. Park, University of Sydney Plant Breeding Institute Cobbitty, and Dr Colin Wellings, NSW Agriculture (seconded to the Plant Breeding Institute Cobbitty)
IMPORTANT EVENTS during the 2001 season included: the detection of a new stem rust pathotype*, which can overcome resistance gene Sr38, in wheat from samples collected in the Esperance region of WA in early November see Ground Cover 39 for more detail); the recurrence of previously observed stripe and leaf rust pathotypes that can grow on wheat containing respectively Yr17 and Lr24 resistance genes; and the isolation of a new oat leaf rust from Queensland that causcd discase on the cultivars Bettong and Barcoom
* new pathotypc is a new type of rust distingui shed by which resistance genes it can overcome.
Leaf rust on wheat - how do current cultivars stack up?
The wheat rust pathotype that grows on wheat containing the Lr24 resistance gene was commonly isolated from samples sent in from SA, northern NSW and Queensland, and was also detected in samples forwarded from Victoria and southern NSW. This pathotype was detected for the first time in October 2000 and is of importance because 13 currently recommended cultivars carry the Lr24 resistance gene.
Field tests with the Lr24 pathotype have shown that the cultivars Dennis , Giles, Petrie and Sunsoft 98 are resistant, that Anlace , Babbler , Cunningham, Datatine, Janz, Lang , Mira , Mitre , Mulgara , Perouse, Tasman and Sunpict are moderately susceptible, and that Krichauff and Worrakatta are susceptible.
Stem rust on wheat - Western Australian varieties of concern
Stem rust was rare in eastern Australia during 2001 , and this has been the pallern for many years. Samples were forwarded from WA, including those collected in the Esperance region in early November, from cullivar Camm , which carries the VPM resistance - a triple rust resistance source that includes not only stem rust (gene Sr38) but also leaf rust (Lr37) and stripe rust (Yr17).
These samples were later shown to be a rust pathotype that can grow on wheat with Sr38, which was the first reported occurrence in Australia. Camm should now be regarded as susceptible to stem rust in WA, but it may be less susceptible than Westonia or Yitpi . In addition to Camm , other Australian cultivars with the VPM resistance include Trident, Bowie, Sunbri, Sunlin, Sunstate , Stylet and the winter wheat Rudd . Initial tests have indicated that at least some of these cultivars have additional stem rust resistance to the new pathotypc, although further testing is needed to gain beller knowledge of what genes are present.
It is important to note that Lr37 remains effective in protecting against leaf rust in all regions of Australia.
Strip rust on wheat - Camm high levels
Wheat stripe rust was common in southern regions of eastern Australia, with first reports from northern NSW in late August. A pathotype that overcame the stripe rust component of the VPM resistance, Yr17, first detected in eastern Australia in 1999, was again detected in 200 I in northern and southern NSW, Victoria and SA. Field collections in 2001 from Camm indicate that this cultivar supports unacceptably high levels of stripe rust. It is expected that other cultivars with Yr17 (see above) carry additional resistance of both seedling and adult plant types which will provide effective protection against this pathotype.
Rusts of barley - leaf rust concern
Leaf rust of barley was present in all states, and pathotypes that infected barley with the gene Rph12 (present in Franklin , Fitzgerald , Gairdner , Tallon, Lindwall ) dominated in all. Samples from WA yielded mainly a new pathotype, present in samples from Moora, Badgingarra, Esperance, Yandanooka and Well stead. The origin of this pathotype is not known as it possesses several features that make it distinct from other contemporary Australian pathotypes of barley leaf rust.
No reports were made of stem rust in commercial barley crops during 2001. Barley grass stripe rust, while common, was less severe than in the 2000 season and no crop damage was reported.
Rust of oats - no cultivars with resistance to leaf or stem rust
Of importance was the detection of a new leaf rust pathotype that can infect Bettong and Barcoo , in a sample collected from Gallon, Qucensland. The pathotype responsible appears to be a single-step mutant from an existing one, and it now seems that, in the north at least, there are no oat cultivars with resistance to leaf rust.
Similarly, although the stem rust resistance gene Pga was affected by a pathotype in 2001, its detection in earlier years means that no current oat cultivars possess effective resistance to stem rust.
Likewise for stem rust, even though pathotypes infecting oats carrying the Pga resistance gene were not recovered during the 2001 survey period, their detection in previous years means that there are no current oat cultivars with effective stem rust resistance.