| | Introduction | Materials and methods | Results | Conclusions | Acknowledgements
Introduction
Barley (Hordeum vulgare L.) production in Alberta averaged around 6 million metric tonnes from 2 million hectares annually, and accounted for close to 50% of the total barley production in western Canada. Scald incited by Rhynchosporium secalis J.J. Davis has caused considerable yield and quality losses, resulting in annual estimated monetary losses of $7 million in Alberta.
Resistant cultivars have been used for control of scald of barley. However, some cultivars have shown increasingly susceptible reactions to this disease, suggesting a breakdown of resistance as a consequence of changing pathotype composition and frequency. As a result, the status of cultivar resistance should be constantly monitored in relation to changes in pathotypes. The objectives of this study were to evaluate the resistance of commercial cultivars to scald of barley, and to examine the effectiveness of major resistance genes in Alberta.
Materials and Methods
Hill plots were established at various locations in Alberta. In each test, 9 barley accessions with major resistance genes and 35 commercial cultivars were planted and replicated four times for 1997-1999 (Period 1). Twelve accessions and 42 commercial cultivars were used for 2000 and 2001 (Period 2). Visual assessment of disease severity was made and disease severity data for each test were converted to percentage severity relative to the average of three susceptible cultivars, Argyle, Harrington and Jackson. Correlation analyses were used to compare scald reactions in the accessions between the two periods. Correlation and cluster analyses were also carried out to determine the differential responses of the commercial cultivars between the two periods.
Results
There was no apparent change in scald reactions for the accessions between the two test periods, as indicated by the high level of the correlation coefficient (R2=0.86**) (Fig. 1). This suggests that these genes are continuing to remain effective against the major pathotypes in Alberta and these genes can be potentially useful as sources for breeding resistance.
Scald reactions for the commercial cultivars showed a correlation coefficient of R2=0.56** between the two periods, (Fig. 2). The relatively low coefficient value compared with that for the accessions suggested that some cultivars changed scald reactions over the test period.
Further comparisons in scald severity showed that the susceptible cultivars (arrow) were grouped independently from other cultivars for the first test period (Fig. 3). However, these same susceptible cultivars (arrows) were grouped with nine cultivars including CDC Earl, Winchester, CDC Dawn, CDC Richard, CDC Guardian, etc., in the second period (Fig. 4). The change in grouping between the two periods indicates that the resistance in these nine cultivars that had been rated as resistant when released for commercial production had broken down. A high level of resistance remained in cvs. AC Stacey, Seebe and Kasota, as shown by their independent grouping in both periods (Figs 3 and 4). No major changes were found for other cultivars.
Conclusions
- The genes in the accessions provided effective resistance to the major R. secalis pathotypes across Alberta.
- Resistance in some commercial cultivars was overcome as a result of changing pathotype frequency and composition.
- The difference in scald reactions between accessions and some of the commercial cultivars suggests a different genetic basis for scald resistance between these two host groups.
- The scald pathogen’s variability will necessitate the ongoing monitoring of the resistance in accessions and commercial cultivars.
Acknowledgements
The authors thank the technical assistance of C. Bos, D. Clark, D. Runge, A. McCarty, A. Olson, D. Orr, N. Rauhala, K. Yaworsky and the Gateway Research Organization. This study was partially funded by grants from the Alberta Barley Commission and the Alberta Agricultural Research Institute.
K. Xi1, T.K. Turkington2, M. Cortez1, J.H. Helm1, P. Juskiw1 and J. Nyachiro1
1 Field Crop Development Centre
2 Agriculture & Agri-Food Canada, Lacombe Research Centre
Presented at the 2002 North American Barley Researchers Workshop, September 22-25, 2002, Fargo, North Dakota |
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