Background/context:

Yellow spot in wheat caused by the fungus Pyrenophora tritici-repentis (Ptr) is a disease which can cause significant economic losses in years with conditions conducive to disease development. In the 1998/1999 season, yield and quality loss in wheat due to yellow spot exceeded $190 M in northeast Australia alone.

 Aim:

The overall aim of this project was to make screening for yellow spot resistance in wheat more effective. When this project commenced, the screening program for yellow spot resistance at the DPI&F Leslie Research Centre involved spraying wheat with conidia collected from infected plants in the field. The disadvantages of this method were that the supply of conidia was dependent on favourable weather conditions; the inoculum was not characterised as to what pathotypes may be present, and the inoculum contained spores of non-target fungi.

Major Outcomes:

The critical milestone of this project was the development of a protocol for the effective mass production of Pyrenophora tritici-repentis conidia from different races and pathotypes under controlled conditions. This protocol improves the consistency and effectiveness of screening for resistance to yellow spot. A hydroponic seedling system, developed by Dr. Williamson, rapidly and cost-effectively screens a significantly larger number of wheat lines than the former potted plant system.

Analysis of the population structure in Australia of Pyrenophora tritici-repentis revealed that the isolates belong to one race, but contained considerable variation in aggressiveness. Molecular markers indicated that the fungus reproduces sexually and is probably the reason for the variation in aggressiveness. It is recommended that populations of Pyrenophora tritici-repentis be assessed occasionally for increased or changed virulence on an extensive wheat differential set to ensure that isolates with the broadest virulence spectrum and the highest level of aggressiveness are routinely used for resistance screening programs.

For more information contact:

Dr André Drenth
Department of Primary Industries and Fisheries
Phone: +61 (0)7 3896 9345
Email: Andre.Drenth@dpi.qld.gov.au