Stem Rust (Puccinia graminis)
Much less barley stem rust was found in the northern plains in 1996 than in previous years. In mid-July, traces of stem rust were found in a field in south central South Dakota, in plots in west central Minnesota, and in plots and fields in northeastern North Dakota. Traces of stem rust were also found on wild barley (Hordeum jubatum) along the roadside in northeastern South Dakota. In early August, traces of stem rust were found in plots and fields in eastern North Dakota.
The low of incidence of stem rust in barley in the northern plains in 1996 may be attributed to the reduced presence of wheat stem rust race Pgt-QCCJ, which accounted for only 14% of the isolates identified from barley (Table 1). In the previous seven years, more than 60% of the stem rust isolates identified were QCCJ, which is virulent on barley cultivars with the Rpg1 (T) gene for resistance.
The most common stem rust race on barley in 1996 was Pgt-TPMK, which is avirulent on cultivars with the Rpg1 gene. TPMK comprised 59% of the isolates from barley and 72% of the isolates from wheat in 1996, but in 1995 only 3% of the isolates from barley and 42% of those from wheat were TPMK. The reduced frequency of Pgt-QCCJ and the increase in Pgt-TPMK may be due to reduced acreage of winter wheat cultivars susceptible to QCCJ in Kansas.
Pgt-QFCS was the second most common stem rust race found on barley in both 1995 and 1996 at 5% and 21% of the isolates, respectively.
Losses to stem rust in barley were light in 1996 (Table 2).
Leaf Rust (Puccinia hordei).
Although barley leaf rust overwinters in Virginia nearly every year, only trace amounts were found in Virginia in 1996. Severe barley leaf rust infection was found in a plot in south Texas during the last week of March. Other plots in the same nursery had lighter amounts of leaf rust infection. Traces of barley leaf rust were found in southern Illinois in early June. During the second week of June, leaf rust was found in plots in Guelph, Ontario, where it likely overwintered.
In southern Minnesota, traces of leaf rust were found in barley plots during the third week in June. Later in June, traces of barley leaf rust were found in plots in east central South Dakota and west central Minnesota. In early July, traces of leaf rust were found in a barley field in west central Minnesota, and in mid-July wild barley (Hordeum jubatum) along the roadside in southern Minnesota and northeastern South Dakota had traces of barley leaf rust. In August, traces of leaf rust were found in plots and a few barley fields in northeastern North Dakota.
Losses to barley leaf rust were minimal in 1996 (Table 2).
Twelve differential barley genotypes were used to identify races of P. hordei (Table 3). These races were designated according to the system of Roelfs and Martens (Phytopathology 78:526-533) as shown in Table 4. Seven races of barley leaf rust were identified from collections in 1996. The most common were race RHD, which was found in Texas and California, and race MCJ, which was found only in North Dakota (Table 5).
Stripe rust (Puccinia striiformis)
Barley stripe rust became firmly established in the Pacific Northwest, where the climate is most favorable for its development. As stated last year, this is a classic example of a disease finding its niche and increasing at a fast rate over a large area.
By the third week of March, barley stripe rust was found in nurseries in the Sacramento Valley (Sacramento and Sutter Counties) of California. By the last week in April, stripe rust was severe in susceptible barley cultivars in fields and nurseries in the San Joaquin and Sacramento Valleys. Most barley cultivars in the U.S. are susceptible to stripe rust, but some of the lines in the nurseries were resistant. California reported a 15% yield loss to stripe rust in 1996 (Table 2), which is the greatest loss to barley stripe rust ever recorded in the U.S.
In mid-April, plots of winter barley trials at Corvallis in northwest Oregon were heavily infected with stripe rust. The rust developed first in susceptible border rows and then spread quickly to other cultivars in the plots. The most heavily rusted plants had 100% stripe rust on the bottom three leaves. By early May, stripe rust infection centers were observed in plots of winter and spring barley cultivar trials in northeastern Oregon (Fig. 1).
In early May, moderate levels of barley stripe rust were found in fields in eastern Washington, while 40% stripe rust severity was reported in experimental plots in the same area. In mid-May, severe stripe rust was reported in experimental barley plots on the western side of the Cascades in Washington. By early June, some western Washington winter barley plots had 100% stripe rust infection, but plots of spring barley had trace infection.
In mid-June, stripe rust was severe on winter barley in irrigated plots in north central Oregon, winter barley plots in southwest Idaho, and fields and plots of winter barley in northern Idaho. During the first week in July, stripe rust was increasing in fields and plots of spring barley in northern Idaho and eastern Washington, and by mid-July, stripe rust was severe on the most susceptible cultivars. In early August, light stripe rust was reported in a spring barley trial plot in the Flathead Valley of northern Montana.
The barley cultivars grown in the Pacific Northwest exhibited a range of levels of adult plant resistance to stripe rust. In addition, an emergency label was obtained for use of Folicur to control stripe rust on barley in the Pacific Northwest. Consequently, losses to stripe rust in barley were relatively light (Table 2).
Crown rust (Puccinia coronata). Barley plants in a nursery in east central South Dakota had 15% crown rust severity in mid-June, which increased to 60% by mid-July. Also, in mid-July, 25% crown rust severity was seen in plots and fields of barley and in wild barley in southeastern North Dakota. By late July, severities reached near 100% in some North Dakota plots of the most susceptible barley cultivars.
In spite of the severe crown rust infections in isolated sites, this
disease has not caused significant damage on a statewide level, because
its distribution is still very limited. It appears that crown rust of barley
is still restricted in relatively close proximity to buckthorn bushes,
its alternate host.
Table 1. Races of Puccinia graminis f. sp. tritici identified from barley in 1996.
|Number of||Percentage of isolates of Pgt-race?|
Table 2. Estimated losses in barley due to rust in 1996.
|1000||Yield in||Production||Stem rust||Leaf Rust||Stripe rust|
|State||harvested||per acre||of bushels||percent||bushels||percent||bushels||percent||bushels|
Table 3. Barley genotypes used to differentiate isolates of Puccinia hordei.
|Infection phenotype of pathogen and barley Rph genes|
Table 5. Races of Puccinia hordei identified from the United States in 1996.
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