Cereal rust corner with Colin Wellings¹, Robert Loughman², Harbans Bariana³, John Majewski⁴:Unusual stripe rust in WA: likely origins and threat level

STRIPE RUST, caused by the fungal pathogen Puccinia striiformis, was identified in a Stiletto wheat crop on 21 August 2002, in the Lake Grace district of WA.

Test results at the Cereal Rust Laboratory at the Plant Breeding Institute, University of Sydney, indicated that the WA pathotype (or race or strain) is quite different from pathotypes known to occur in eastern Australia. It was concluded that the widespread outbreak in the southern districts of WA was due to the introduction of a foreign pathogen.

Approximately 140 samples are being tested at the Cereal Rust Laboratory. This will indicate the pathotype diversity in the initial outbreak, and the expected disease responses of varieties.

The early observations raised several issues: the expected disease responses among commercial varieties, the threat posed to eastern wheat growers should this pathotype migrate, and the likely source of the new pathotype.

Although the WA pathotype is distinctly different from those in the east, its particular combination of ill-effects on crops does not represent a new threat to the wheat industry — that is, its pathogenic ability is generally represented in pathotypes already present in the east.

What is the disease response likely to be?

The data in Table 2 indicate the expected field responses of wheat varieties in eastern Australia compared to observations made in WA during the current season. Although this data from WA is preliminary, and often the result of single observations at certain trial sites, it does indicate that stripe rust responses between eastern and western Australia are within the same range.

The differences in variety responses between east and west are minimal, although there are exceptions. For example, Spear is somewhat more resistant to the WA pathotype than it is to pathotypes in eastern Australia.

An unexpectedly high response on the variety Angas was recorded at one trial site in WA (data not shown in Table 2). This suggests that the resistance gene Yr10 in Angas may not be effective, although tests to date have not confirmed the possibility.

Where did the rust come from?

Cereal rust pathogens are capable of long distance movement on wind currents. Therefore South Africa, which has had the disease since 1996, was considered a possible source of the WA pathotype. However, the respective pathotypes are quite different. It is possible that pathotypes of eastern and central Africa could be involved, but recent data are not available.

Published work from the USA indicate pathotypes of similar features to the initial pathotype in WA, making it another candidate region of origin.

While the origin remains unclear, it is highly likely that the pathogen was introduced on the contaminated clothing of travellers. This continues to remain an important issue in the introduction of exotic pathogens, and includes both new pathogens and new pathogenic variants of existing pathogens. Contaminated clothing also represents a significant risk for movement of different rust strains around Australia

KEY MESSAGES:

International and interstate travellers should avoid the possibility of moving rust spores by ensuring clothes arethoroughly washed and footwear cleaned prior to visiting crops.

Should the WA pathotype migrate, eastern Australian varieties are expected to respond in the same way as they do to the current eastern pathotypes.

Ongoing monitoring remains crucial to detect any variant pathotypes that may potentially cause problems to commercial wheat varieties.

Farmers, advisers, researchers are encouraged to send diseased leaves in paper envelopes with clearly marked details of location, variety if known, and sender contact information to:

Australian Cereal Rust Survey

Plant Breeding Institute

Private Bag 11, Camden NSW 2570

Table 1: Pathogenic characteristics of pathotypes of stripe rust (Puccinia striiformis) on certain resistance genes known to be present in Australian wheat cultivars. The "+" indicates virulence (i. e. the ability to cause disease on the particular resistance gene) and so varieties with this gene alone will not be protected against stripe rust.
Resistance geneWA pathotypeEastern pathotypes
&nbsp134 E16 A+110 E143 A+238 E143 A+104 E137 A-, Yr17+
Yr6(e.g. Stiletto)
+
+
+
-
Yr7 (e.g. WestoniaPBR logo)
+
+
+
-
Yr9 (e.g. Warbler)
+
-
+
-
Yr10 (e.g. Angas)
-
-
-
-
Yr17 (e.g. CammPBR logo)
-
-
-
+
YrA (e.g. Rosella)
+
+
+
-
— (e.g. Spear)
+
+
+
+
Table 2: Disease response in the field to stripe rust (caused by Puccinia striiformis). Numbers refer to approximate percentage leaf area affected by the disease. The high scores in brackets for certain varieties (Bowie, CammPBR logo) indicate the disease response when exposed to the pathotype virulent in eastern Australia for the resistance gene Yr17 present in these wheats. R (resistant), MR (moderately resistant), MS (moderately susceptible), S (susceptible)
VarietyDisease response in eastern AustraliaDisease response in western Australia
AnnuelloPBR logo
R-MR
MR
Aroona
MS-S
S
BowerbirdPBR logo
MR-MS
MS
Bowie
R (MR-MS)
R
CammPBR logo
R (MS)
R
CharaPBR logo
MR
R-MR
Diamondbird
MR
MR
Frame
MR-MS
MR-MS
Hartog
R
R-MR
H45PBR logo
MS-S
S
Halberd
MS
MR-MS
Janz
MR
MR
Krichauff
MR-MS
MS-S
LangPBR logo
MR
MR
Lowan
MR
MR
Machete
MS
MS-S
MiraPBR logo
R
R
MitrePBR logo
MR
MR-MS
MulgaraPBR logo
MR
MR
Rosella
MR
MR
Schomburgk
S
S
SilverstarPBR logo
MR
MR
Spear
MS-S
MR-MS
Stiletto
MS
MS-S
Sunco
MR
R-MR
Whistler
MR
R-MR
WyalkatchemPBR logo
MS
MR-MS
#185; Dr Colin Wellings, Plant Breeding Institute, The University of Sydney, Cobbitty, NSW (on secondment from NSW Agriculture)

#178; Dr Robert Loughman, Crop Improvement Institute, Department of Agriculture, South Perth, WA

#179; Dr Harbans Bariana, Plant Breeding Institute, The University of Sydney, Cobbitty, NSW

#8308; Mr John Majewski, Crop Improvement Institute, Department of Agriculture, South Perth, WA