Graingrowers have been warned to take special care with paddock hygiene this summer—with total elimination of volunteer wheat plants — after confirmation in South Australia of a race of leaf rust that has broken down one of the wheat industry's most valuable resistance genes, Lr24.
Volunteer plants allow rust to survive over summer and infect the following year's winter wheat crop.
The call came from Queensland Department of Primary Industries (QDPI) wheat breeder John Sheppard, who said the South Australian discovery of leaf rust in wheat varieties Krichauff, Worrakatta and Janz had implications for other northern varieties like Cunningham, Sunco and Lang, which relied for resistance on the Lr24 gene.
"Confirmed loss of the Lr24 material will be a major setback for Australian wheat breeding, due to the loss of advanced breeding lines," Mr Sheppard said. "Observations so far have been confined to South Australia, but the later season in the south still allows time for the new rust strain to spread to Victoria and southern NSW.
National Cereal Rust Control Program (NCRCP) scientists identified new strains of pathogen on a set of differential testers known to carry genetically characterised rust resistance genes. They were able to say the new strain did not attack the leaf mst resistance genes Lrl3 and Lr37, which were present — either singly or in combination — in the varieties Hartog, Rowan, Leichhardt, Houtman, Strzelecki, Sunstate, Sunlin and Sunvale.
According to fellow rust pathologist Harbans Bariana, NCRCP scientists believe the new rust outbreak will be more widespread than the initial discovery on the Yorke Peninsula.
"I visited several wheat breeding trial sites around Adelaide, and observed leaf rust development on Krichauff and Janz. In the absence of the new strain, these wheats should be free of leaf rust," Dr Bariana said. "Some 250 elite wheat lines from the various Australian breeding programs are currendy being tested against the new strain."
Mr Sheppard said it was far too early for growers to be considering variety choices in the wake of the South Australian outbreak, because some varieties with Lr24 might be partially protected against the new rust strain by additional resistance genes.
The incident was a timely reminder of the need for the industry to do eveiything possible to protect valuable resistances in plant varieties through gene combinations.
Up to 50 per cent yield loss
Leaf rust had the potential to cause up to 50 per cent yield loss in highly susceptible varieties under conditions of heavy infection. However, the majority of northern Australian wheat varieties carried varying levels of uncharacterised, adult plant resistance to minimise losses in a worst case scenario.
Contact: Mr John Sheppard 07 4639 8888, Dr Harbans Bariana 02 9351 8809