Barley cultivars grown in many parts of the world including the U.S.A. have been resistant to barley leaf rust caused by Puccinia hordei Otth. Single genes (Rph3, Rph7 and Rph9) have been deployed most widely; however, virulence to these genes exists and has caused great concern among commercial breeders because these resistance genes have been considered most effective. Sources of leaf rust resistance that possess genes which are effective to a broad spectrum of P. hordei are rare. However, such resistance genes have been identified either singly or in combination with other genes in some Hordeum vulgare L. and Hordeum vulgare spp. spontaneum accessions. Thirteen resistant spring barley accessions originating from diverse locations worldwide were studied to characterize inheritance of resistance. The accessions were crossed with each other and to barley host differential lines to determine allelic relationships. The resistant parents also were crossed to susceptible parents ‘Moore' and/or ‘Larker' to characterize gene number and gene action for resistance to P. hordei. Seedlings of the parents, F₁, F₂, BC₁F₁ (Moore or Larker x F₁) and F₃ populations were evaluated in the greenhouse for their reaction to P. hordei race 30. All of the accessions were resistant to race 30. Genetic analysis showed that resistance in eight of the accessions CR270.3.2, CR366.13.2, ‘Caroline', ‘Deir Alla 105', ‘Giza 119', ‘Gloria', ‘Collo sibling' and ‘Lenka' is governed by an allele at or near the Rph3 locus. Caroline and CR366.13.2 may possess a second unknown recessive gene in addition to Rph3. The accessions ‘Grit' and ‘Donan' possess an allele at the Rph9 locus, and ‘Dorina' and ‘Femina' possess alleles at the Rph3 and Rph9 loci. Resistance in ‘Carre 180' to race 30 is governed by an unknown recessive gene. Results obtained from this study provide a better understanding of the inheritance of resistance to P. hordei in these barley accessions. It also facilitates a systematic use of leaf rust resistance genes in breeding programs for improvement of barley cultivars.

Scald of Barley in Alberta: Disease Resistance Screening, Breakdown and Management

T. K. Turkington¹, P.A. Burnett², K.G. Briggs³, K. Xi⁴, D.D. Orr¹, J.H. Helm⁴, B.G. Rossnagel⁵, W.G. Legge⁶, and J.P. Tewari³

1Lacombe Research Centre, Agriculture and Agri-Food Canada, 6000 C&E Trail, Lacombe, AB, T4L 1W1; ²Lethbridge Research Centre, Agriculture and Agri-Food Canada, P.O Box 3000 Main, Lethbridge, AB, T1J 4B1; ³Department of Agricultural, Food and Nutritional Science, Faculty of Agriculture, Forestry and Home Economics University of Alberta, Edmonton AB Canada T6G 2P5; ⁴Alberta Agriculture, Food and Rural Development, 5030 50 St. Lacombe, AB, T4L 1W8; ⁵Crop Development Centre, University of Saskatchewan, Saskatoon, Saskatchewan S7N 0W0; ⁶Brandon Research Centre, Agriculture and Agri-Food Canada, 18th Street and Valley Road, P.O. Box 1000A, RR #3, Brandon, Manitoba R7A 5Y3

The province of Alberta accounts for close to 50% of the total barley acreage in western Canada, which is estimated to be over 5 million acres. In Alberta, scald caused by the fungus, Rhynchosporium secalis, is one of the main leaf diseases of barley. Average yield losses due to scald may be as high as 5-10%, with monetary loss estimates of over $30 million depending on the year. Currently, one of the main management tools for scald, especially for feed barley production, has been the use of resistant cultivars. Ongoing evaluation of breeding material for resistance to this disease is required due to changing virulence patterns in the scald pathogen, lack of resistance in malting barley, public desire for sustainable/environment friendly crop production and more intensive barley production coupled with increased demand for barley. The objective of the current project at the Lacombe Research Centre, Agriculture and Agri-Food Canada, is the coordination of scald screening for barley breeding programs in western Canada. From 1995 to 1997, a total of over 37,000 hill plots were evaluated for scald reaction at the Lacombe Research Centre and the University of Alberta. Most candidate cultivars, with scald resistance, currently going through the cooperative variety testing system were first identified as part of this scald screening project. Hill plots were comprised of germplasm, breeding lines, checks, material from the Alberta Regional Variety Trial, and candidate barley cultivars going through the Prairie Registration Recommending Committee for Grain, Western Cooperative Tests.

At Lacombe, hill plots were inoculated with scald infected straw collected from the previous year as well as a spore suspension of the scald fungus. At Edmonton, hills were only inoculated with scald infected straw collected from the previous season. Disease assessments at Lacombe were based on a 0-9 scale, while at Edmonton a 1-9 scale was used. Disease development was typically scored three times at Lacombe starting in early July and one to two times at Edmonton starting in late July. Scores from both sites were tabulated and supplied to the cooperating breeding programs for their information and use in assessing which lines to advance and what further crosses to make. Regional trial ratings were used to confirm the assigned ratings in the Varieties of Cereal and Oilseed Crops for Alberta – 1995-97, AGDEX 100/32. Ratings from the cooperative screening trials were used as part of the evaluation of candidate cultivars in the cooperative variety testing system.

In 1995 and 1997 at Lacombe and Edmonton, and in 1996 at Lacombe, the extent of disease development was high enough to permit the effective differentiation of susceptible and resistant breeding material. Multiple disease assessments were used by the western breeding programs to evaluate material for the phenomenon of "slow scalding." This type of response is where lines exhibit some symptoms of scald, but the disease does not build up to high levels on the upper leaves, translating into reduced yield losses and selection pressure for more virulent races of the scald fungus. Low disease pressure at Edmonton in 1996 did not permit effective differentiation of disease reaction for most material. Variation in weather conditions from year to year and their resulting influence on disease development, stress the need for the continuing presence of scald screening nurseries at both Lacombe and Edmonton.

In the regional trials from 1995 to 1997, disease ratings as a percentage of Harrington, a susceptible cultivar, were relatively high for several resistant cultivars including CDC Dawn, CDC Earl, CDC Guardian, Falcon, AC Lacombe, and Leduc. Overall, regional trial results indicated the development and increased influence of more virulent races of the scald pathogen at Lacombe and Edmonton. These results are of major concern with regard to the appearance and increased prevalence of these more virulent scald races. As a result of these races the resistance genes in cultivars like CDC Earl, CDC Dawn, and Falcon may no longer be effective at certain locations in Alberta. In addition, they may not represent an effective source of resistance that can be incorporated into adapted cultivars by western Canada barley breeders.

For long-term scald management it is critical that potential sources of scald resistance continue to be identified and incorporated into commercially acceptable breeding material and that we start to look at ways of managing the resistance that is already present in our western Canadian cultivars. Options need to be identified to help producers manage and prolong the usefulness of current and future sources of scald resistance. One potential option, being investigated at Lacombe, is for producers to rotate barley cultivars with different sources of resistance, which would be analogous to rotating herbicides with different modes of action; a practice producers are using to prevent the development of herbicide resistant weeds. Different cultivars may not have the same source of disease resistance, especially if they are from different breeding programs. Rotating cultivars with different sources of resistance may not only help to lower disease levels and increase yields, but also reduce the selection and build-up of virulent pathogen races, thus prolonging the usefulness of a particular source of resistance.