A NEW stem rust pathotype with the ability to overcome resistance present in several wheat cultivars including Camm was detecte':fin samples of stem rusted wheat collected in the Esperance region of WA late last year. Tests of stem rusted wheat collected from other parts of Australia in 2001 indicate that, at this stage, the new pathotype appears to be restricted to the Esperance region.
The new pathotype closely resembles one that has been common in WA in recent years, but has added virulence for the resistance gene Sr38, present in Camm and several other Australian wheat cultivars. This is the first time virulence has been reported for Sr38 in Australia. This gene forms part of what is known as the VPM resistance, originally transferred to common wheat from the wild relative Triticum ventricosum.
The VPM resistance is a triple rust resistance that includes not only stem rust but also leaf rust (gene Lr37) and stripe rust (Yrl7). It is important to note that Lr37 remains effective in protecting against leaf rust in all regions of Australia. Virulence for the stripe rust component Yr17 was detected in eastern Australia in 1999, 2000 and in 2001.
Camm should be regarded as susceptible to stem rust in WA. 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 pathotype, however further testing is needed to gain better knowledge of what genes are present.
The additional genes should provide some protection against this new pathotype in adult plants as well as seedlings.
Summer protection strategy
It will be critical to control cereal volunteers over summer, should they develop prior to planting. In particular, paddocks of Camm and Westonia in all areas, and particularly in the Esperance region, should be grazed or sprayed out immediately volunteers start to develop and well ahead of initial plantings.