Rust samples received by the University of Sydney’s Plant Breeding Institute (PBI) in June and July point to pathotypes expected to dominate an anticipated spring rust epidemic in eastern Australia.
PBI pathologist Dr Colin Wellings says the performance of varieties in the early phase of the stripe rust epidemic is generally as expected.
“The most distinct difference between this season and last has been the first appearance of stripe rust in southern NSW in June, compared to a northern NSW focus from May in 2009,” Dr Wellings said.
“The more advanced northern crop in 2009 provided greater opportunity for disease spread, compared to a southern origin where cold conditions and a later disease onset may have contributed to reduced inoculum pressure.”
The Grains Research and Development Corporation (GRDC) supports PBI and rust research in northern NSW and southern Queensland.
The samples identified to date indicate an even frequency of the ‘Jackie’ and ‘WA Yr17’ stripe rust pathotypes.
This represents another contrast with previous seasons where the ‘WA Yr17’ pathotype seemed to arrive much later in the epidemic.
“The clear implication for 2010 is that varieties carrying the Yr17 resistance and known to be vulnerable to the ‘WA Yr17’ pathotype (Barham, Bowie, Camm, Derrimut, Endure, Fang, Hornet, Mace, Marombi, Pugsley, QAL 2000, Sunstate, Ventura, Yenda, Young) may need fungicide intervention, especially where stripe rust begins early,” Dr Wellings said.
“Other Yr17 varieties considered intermediate in response to the ‘WA Yr17’ pathotype will also need to be monitored carefully in the early phases of disease occurrence, as a fungicide application may be beneficial in reducing inoculum pressure.”
Notable among these varieties is Crusader, which is rated moderately resistant to moderately susceptible, but may show relatively high levels of stripe rust at tillering.
Dr Wellings says a fungicide applied at first disease occurrence would be expected to position this variety favourably for spring.
“The resistance gene Yr33 continues to provide good protection in varieties Gregory and Strzelecki.
“However, it should be noted that Gregory is slightly heterogeneous for stripe rust resistance and some plants are noticeably more susceptible.
“An early fungicide on Gregory should be all that is required for protection through late winter.”
Dr Welling says several varieties are vulnerable to yellow leaf spot and will be at risk in wheat on wheat rotations.
Fungicides are available that combine both yellow leaf spot and stripe rust control.
In seasons such as this one, reduction of lower leaf infections from one or both diseases will place crop canopies in a favourable situation to capitalise on anticipated ideal spring conditions, he said.
“Sample numbers have been noticeably less in 2010 compared to the previous season,” Dr Wellings said.
“At mid August in 2009, 130 samples were tested compared to 67 in the current year.”
Wheat stem rust has been detected at widely separate locations throughout eastern Australia since April, including Glen Innes in northern NSW.
Apart from the samples forwarded from Glen Innes, which were identified as pathotype 34-2,12,13, all samples processed so far have been identified as pathotype 34-1,2,7 +Sr38.
Ten samples of wheat leaf rust have been received to date, from locations throughout eastern Australia including Warwick, Queensland; and Dunedoo, Jerilderie and Delegate, NSW.
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