Background
Barley strip rust (Puccini striiformis f. sp. hordei) is now found in all major malt barley producing areas of the western U.S. In 1995, it developed in the northwest (Oregon and Washington) and caused significant damage. While it has been know in South America since 1975, it only spread to the U.S. in 1991 when it was found by Dr. David Marshall in Uvalde, Texas. Since then it has spread throughout the western U.S. and into Canada.
Barley screening trials were started in the 1990/1991 cropping season in Cochabamba, Bolivia by the authors at the instigation and in cooperation with Dr. Darrell Wesenberg, Director of the USDA/ARS Small Grain Germplasm Research Laboratory at Aberdeen, Idaho and his staff. This report covers the 5th year of screening in the program.
The 1995 South American Trials
In 1995, field plots were again established in Cochabamba, Bolivia in cooperation with the national barley research program under the leadership of Ing. Juan Cordova and with Ing. Velasco's (CSU) supervision. The 1995 plantings were composed of several different trials.
Group I:
Entries in this group include a continuation of the National Small Grain Germplasm Collection (NSGC) not previously tested (there are over 30,000 accessions in the NSGC). These are all lines that have not been previously tested in Bolivia or elsewhere for reaction to barley stripe rust. There were 3,172 lines in this group in 1995 that were tested only in Cochabamba.
Group II:
The 289 lines in this group are all NSGC selections or "in-house" varieties and selections with R, MR or "0" barley stripe rust readings in the 1994 evaluation nursery. This group (sometimes called "elite") was also planted in other locations as follows:
Group III:
The 1,571 entries in this trial included selected Aberdeen F3 materials and entries from other institutions and commercial programs. Institutions and other submitting lines for this trial were 1-USDA/ARS Aberdeen, 2- North Dakota State University, 3- Oregon State University, 4- Washington State University: 5- Utah State University; 6- Texas State University; 7- Montana State University; 8- University of California-Davis; 9- Adolph Coors; 10- Busch Agriculture Research Inc. (BARI); 11- Western Plant Breeders and 12- Plant Breeders. These entries were planted at Cochabamba, Bolivia only. Results have been forwarded to Aberdeen and passed on to the respective cooperators.
Barley Stripe Rust Differential Nursery
A differential nursery was developed in cooperation with Dr. Mareike Johnston at Montana State University. These nurseries have been planted at the same sites as the Group II ("elite") lines, ie. Bolivia, Colorado, Germany, Mexico and prior to 1995 in Ecuador. These nurseries have shown considerable variation in reactions to barley strip rust both in years and locations.
Results:
Over 5,000 barley entries were evaluated in 1995 at Cochabamba, Bolivia for reaction to barley stripe rust and are recorded in GRIN system. Results from the Group I (NSGC) lines showed very little resistance (Table 1).
Table 1. Barley germplasm screening for barley strip rust, Cochabamba, Bolivia, 1995.
| GROUP | 0 | R | MR | MS | S |
| % | % | % | % | % | |
| NSGC | 0.4 | 0.2 | 0.0 | 8.2 | 90.5 |
| ELITE | 14.9 | 10.0 | 18.7 | 41.2 | 15.2 |
| COOP. | 0.2 | 0.6 | 0.7 | 25.7 | 72.8 |
Of the lines showing in the range of 0 to MS (9.5%) in group I, most were in the MS group.
Group II ("Elite") lines continued to show a high degree of resistance (Table 1). Over the 5 year period this group of "elite" selected lines has consistently showed effective identification of promising lines (Table 2).
Table 2. Comparison of barley stripe rust elite field results, Cochabamba, Bolivia, 1991 - 1995.
| Year | 0 | R | MR | MS | S |
| % | % | % | % | % | |
| 1991 | 8.0 | 5.2 | 3.4 | 30.8 | 52.6 |
| 1992 | 9.2 | 5.5 | 7.2 | 41.7 | 36.4 |
| 1993 | 16.5 | 10.4 | 1.0 | 45.3 | 26.8 |
| 1994 | 22.3 | 7.5 | 4.6 | 30.6 | 35.0 |
| 1995 | 14.9 | 10.0 | 18.7 | 41.2 | 15.2 |
Due to the now recognized variability of the barley stripe rust fungus "race 24", the high level of MS reactions may be especially useful and provide germplasm that is more stable over a period of time. This variation in the Group II ("Elite") lines also continues to show up between locations as well. Our observations and those of others now highlights the extreme variability of what has been termed "race 24" in the past. Group III (Cooperator) lines showed very little resistance (Table 1). But there continues to be a good level of potentially useful MS Material (Table 3).
Table 3. Cooperators lines with resistance in Cochabamba trials from 1992 - 1995.
| Type | 1992 | 1993 | 1994 | 1995 |
| Reaction | # Acc. | #Acc. | #Acc. | #Acc. |
| R | 14 | 55 | 17 | 10 |
| MR | 24 | 16 | 13 | 11 |
| MS | 95 | 204 | 585 | 404 |
| Total | 140 | 305 | 617 | 428 |
| % | 13.7 | 28.1 | 29.1 | 27.2 |
Table 4 summarizes the total amount of screening carried out in Bolivia since the first 1990/1991 trials. As in prior years, there is variation in host reactions between locations. This continues to highlight the considerable variability being found in the barley stripe rust fungus.
Table 4. Barley germplasm screening for strip rust resistance, Cochabamba, Bolivia,
1991 - 1995.
| Source | 1991 | 1992 | 1993 | 1994 | 1995 | Total |
| NSGC | 7,198 | 4,112 | 3,000 | 2,968 | 3,172 | 20,450 |
| Elite | 523 | 2,252 | 520 | 680 | 289 | 4,264 |
| Coop. | - | 1,019 | 1,084 | 2,117 | 1,571 | 5,791 |
| Adv. | - | - | 598 | 200 | - | 798 |
| Total | 7,721 | 7,383 | 5,202 | 5,965 | 5,032 | 31,303 |
Fungicide trials
Integrated fungicide trials were continued in Cochabamba, Bolivia in 1995, where an experiment was conducted using seed treatment and foliar applied fungicides. There appears to be some difference between the two cultivars Russell and 1202 from Busch, but these differences are due to the level of resistance that 1202 has where as Russell is very susceptible. Complete results will appear in 1995 F&N tests produced annually by the American Phytopathological Society.
Yield components varied by cultivar. Kernel weight for Russell was greater with any combination of seed treatment and foliar spray. However, with 1202 the kernel weight did not differ significantly among treatments. Significant differences were found in number of seeds for Russell but not for 1202. Baden alone and in combination with Vitavax followed by one or two applications of Tilt Significantly suppressed barley stripe rust severity and significantly increased yield in the susceptible cultivar Russell. However, those treatments were less effective on the moderately susceptible cultivar 1202. The greatest degree of barley stripe rust reduction over a long period, occurred when seed was treated with Baden in combination with Vitavax followed by one or two applications of Tilt in both cultivars. However, Baden alone and Baden in combination with Vitavax gave very good disease control over a long period, resulting in considerable yield increases in both cultivars.
Discussion and recommendations
While a lot of progress has been made in identifying barley stripe rust resistance sources, there is still a mjaor problem with reliable resistant lines being deployed in the near future. Presently there is no commercially available material that has incorporated the identified resistance to the level that there is seed ready for commerical distribution.
Even more significantly, the now recognized variability of the fungus poses long range problems. Our work and the work of others has now shown that at least 16 different "pathotypes" can be separated out of "race 24" using differential hosts. Colorado alone has at least three. Therefore, effective management of barley stripe rust will have to depend on an integrated approach such as was outlined in the Proceedings of the 30th Barley Improvement Conference held in Minneapolis January 12, 1995. An integrated approach makes more use of trace to moderately susceptible lines ("slow rusters") in combination with cultural and chemical techniques. This will result in a more stable, long range program of barley stripe rust management.
We, therefore, recommend that the following integrated management approach to barley stripe rust be used.
We would like to acknowledge and thank our cooperators.
Dr. Ursula Walter, (Germany)
Ing. Juan Cardova, (Bolivia)
Dr. Hugo Vivar, (Mexico)
Dr. Mareike Johnston, Montana State University, for continuing to develop and provide both the differential nursery lines for field planting and greenhouse race comparison studies.
Dr. Darrell Wesenberg at the USDA/ARS Small Grains Laboratory, Aberdeen, ID for providing and preparing the barley germplasm materials used in this program.
The USDA/ARS Small Grains Laboratory and the American Malting Barley Association (AMBA) for funding support.
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