Stem rust (Puccinia graminis). The first report of barley stem rust in 1998 was of traces in spring barley plots in early July in southwestern Minnesota and east central South Dakota. During mid-July, traces of stem rust were found in spring barley plots in southeastern North Dakota and west central Minnesota. Traces of barley stem rust were reported in plots, and there was one report of a 70% severity reading in a commercial field in late July in east central North Dakota. In southeastern Washington, stem rust severities of 40% were reported at the soft dough stage in barley varietal plots in late July.
The number of barley stem rust infections found in the U.S. is significantly down from the number found in the mid-1990s. In 1998, only five collections of barley stem rust were received at the Cereal Disease Lab, as compared with 52, 27 and 3 collections in 1995, 1996 and 1997, respectively. The decrease in barley stem rust is probably due to the decrease in the frequency of pathotype Pgt-QCCJ in the P. graminis f. sp. tritici population (Table 1). This pathotype is virulent on the predominant barley cultivars of the Upper Midwest and certain winter wheats in Kansas. The decreased acreage of the QCCJ susceptible winter wheats in Kansas likely resulted in lower inoculum levels of this pathotype. Pathotype Pgt-RCRS was the most commonly identified pathotype in 1998 (46%). Pathotype Pgt-QFCS (31%) and QCCJ (23%) also were identified.
Losses to barley stem rust were light in the U.S. in 1998 (Table 2).
Leaf rust (Puccinia hordei). During the last week in March, 10% leaf rust severities were observed on lower leaves in a few barley plots in southern Texas. Lighter amounts of rust were found in other barley plots in the same nursery. In late April, traces of barley leaf rust were found on cultivars growing in nurseries in central Texas.
In early April, light amounts of barley leaf rust were reported in plots in the San Joaquin Valley of California. Severities of 50-70% were observed in Sutter County (Sacramento Valley) in late April. Leaf rust of barley was light to moderate on susceptible lines at the Yuma, Arizona nursery by late April. Barley leaf rust was generally light in plots throughout the Central Valley of California in mid-May. Severities of 100% were found in nurseries at Davis, California by late May.
By late April, barley leaf rust was light in plots in northeastern Oregon. In early June, barley leaf rust was increasing on spring barley at the late jointing stage near Mt. Vernon in western Washington.
In late April, barley leaf rust was light in plots in eastern Virginia. By late May, leaf rust was moderate (trace - 40%) on winter barley in Virginia.
During the third week in May, barley leaf rust was severe on the lower leaves of susceptible varieties in the Uniform Winter Barley Nursery in central Ohio. Hot dry weather prevented movement of rust to the upper leaves.
During the second week in June, barley leaf rust severities of 80% were reported at the soft dough stage on some susceptible winter barley lines in a southern Ontario, Canada nursery. Rust was just starting to increase on spring barley at this location.
In late June, severities of 5% were reported in barley plots in east central Nebraska, and traces in plots in south central Minnesota while severities up to 50% were observed on barley in central Wisconsin fields. In mid-July, trace to 10% leaf rust severities were observed in barley plots in west central Minnesota, east central South Dakota and southeastern North Dakota. In late July, rust severities of 20% were reported in barley plots in northwestern Minnesota and 5% severities in central North Dakota at the dough stage. Severities of trace to 60% were observed in plots and commercial fields in northeastern North Dakota.
Twelve differential barley genotypes were used to identify pathotypes of P. hordei (Table 3). These pathotypes were designated according to a system similar to that of Roelfs and Martens (Phytopathology 78:526-533) as shown in Table 4. Eleven pathotypes of barley leaf rust were identified from 27 viable collections in 1998 (Table 5). The most common were pathotypes RCD (44%, California, Minnesota, Ohio, Texas, and Virginia) and RCB (19%, California, Minnesota, Ohio, and Texas). As in the past, virulence to Rph1, 2, 4, 8 and 11 was common, while virulence to Rph3, 5, 7, 9 and 12 was absent. These results are similar to what was observed in previous years.
Losses to barley leaf rust were light in the U.S. in 1998 (Table 2).
Stripe rust (Puccinia striiformis f. sp. hordei). In late March, barley stripe rust foci were found in winter barley plots at Uvalde, Texas. Severities of 40% were common in the foci on cultivar Sussex, whereas on other cultivars the severities ranged from trace to 2%.
In mid-April, stripe rust of barley first appeared on susceptible lines in nursery plots at Yuma, Arizona, and by the end of the month, moderate severities were present, and the rust was spreading rapidly. Weather conditions in March and April weather were cooler and much wetter than normal, resulting in favorable conditions for rust development.
In early March, barley stripe rust was found near Corvallis, Oregon and by late March, stripe rust was prevalent in the Skagit Valley of northwestern Washington. In late April, severities of 50% were reported in plots in northeastern Oregon, northwestern and southeastern Washington. By early May, stripe rust on barley was increasing in the Mount Vernon area of northwestern Washington.
In early June, stripe rust on barley was found throughout southeastern Oregon and the state of Idaho. In a southwestern Idaho field, a 90% disease severity at the milk stage was reported and in a northern Idaho field a 20% severity was reported, primarily on the lower leaves. By mid-June, barley stripe rust was increasing on spring barley near Pullman in eastern Washington and Mt. Vernon in western Washington.
By late June, stripe rust on barley was increasing in fields and varietal plots in eastern Washington and northern Idaho. Weather conditions were ideal for rust development under the canopy. Most of the 6-row cultivars were severely infected, while many of the 2-row cultivars were moderately resistant. Some farmers in this area sprayed with a systemic fungicide, such as Tilt or Folicur, to control stripe rust.
By early July, stripe rust on barley in the Pacific Northwest was severe on susceptible spring-sown barleys from the intermountain area of northeastern California, through northeastern Oregon to eastern Washington and northern Idaho. In this area, 50% rust severities were recorded on Steptoe, but on other cultivars with slow-rusting characteristics like Baroness, 5% severities were recorded.
The Pacific Northwest area realized a loss of 1.8% to barley stripe rust in 1998 (3% in Washington , 2% in Oregon, and 1% in Idaho). The loss was much greater than in 1997 when 0.6% losses were recorded for this area (Table 2). In California, there was a 15% loss to barley stripe rust.
Crown rust on barley. By late June, crown rust on barley had developed very slowly at the Brookings, South Dakota nursery as only 5-10% severities were observed on lower leaves of susceptible cultivars at the heading stage. Traces of crown rust were found on barley in the buckthorn nursery at St. Paul. During the second week in July, trace to 1% crown rust severities were observed on barley growing in southeastern North Dakota plots. Light losses to barley crown rust occurred in barley fields growing in close proximity to Rhamnus bushes. Throughout the upper Midwest, crown rust on barley was less severe than in previous years.
Table 1. Pathotypes of Puccinia graminis f. sp. tritici identified from barley in 1998
|State||Source||Number of collections||Percentage of isolates of Pgt-isolates||QCCJ||QFCS||RCRS|
Table 2. Estimated losses in barley due to rust in 1998
|State||1000 acres harvested||Yield in bushes per acre||Production 1000 bushels||Losses due to|
|Stem rust||Leaf rust||Stripe rust|
|%||1000 bushels||%||1000 bushels||%||1000 bushels|
|U.S. % Loss||0.002||0.06||0.89|
Table 3. Barley genotypes used to differentiate pathotypes of Puccinia hordei
Table 4. A proposed North American system of pathotype nomenclature for Puccinia hordei based on 12 differential barley hosts*
|Ph-code||Infection phenotype of pathogen and barley Rph genes|
*Pathotype designations are based on the infection phenotypes of the pathogen isolate on the 12 differential barley hosts. Low = incompatibility (infection phenotypes 0, 0;, 1, or 2) and High = compatibility (infection phenotypes 3 or 4). The infection phenotypes from set 1 determine the first letter of the code, those from set 2 the second letter, etc.
|State||Number of collections||Source||Pathotypes and (number of collections)|
RBD(1), RCG(1), RHD(1),|
MCG(1), MCJ(1), MHG(1)
|Ohio||3||Nursery||RCB(1), RCD(1), RCJ(1)|