Genes for Resistance to Barley Stripe Rust (Puccinia striiformis f. sp. hordei)

Xianming Chen and Roland F. Line

USDA-ARS, Washington State University,

Pullman, WA 99164-6430, USA

Abstract

All possible crosses without reciprocals among 18 barley genotypes that are resistant to races of Puccinia striiformis f. sp. hordei were made to determine what genes are in each genotype and relationships among the genes. Seedlings of parents and F₂ progeny were tested under controlled conditions for resistance to races that were avirulent on both parents. Based on segregation of the crosses and the responses of the progeny to the races, at least 26 of the 30 genes that were detected in the 18 barley genotypes were uniquely different. The single genes in 'Bigo', 'Trumpf', 'Mazurka', and 'BBA 2890' and one of the genes in 'PI 548708', 'PI 548734', 'PI 548747', and 'Abyssinian 14' were linked. One of the two genes in PI 548734 was linked to one of the two genes in 'I 5'. The single gene in 'Cambrinus' and one of the genes in 'Heils Franken' and 'Astrix' were the same or closely linked. The single genes in 'Grannelose Zweizeilige' and 'BBA 809' and the two genes in 'Stauffers Obersulzer', 'Emir', 'Hiproly', and 'Varunda' were different from all other genes and different from each other.

Introduction

Stripe rust of barley (Hordeum vulgare L.), caused by Puccinia striiformis Westend. f. sp. hordei Erikss. (P. s. hordei), is a relatively new disease in the United States. The disease was first observed in Texas in 1991 (Roelfs et al., 1992). Since then, the disease has been detected in Oklahoma, New Mexico, Arizona, Colorado, Utah, California, Idaho, Montana, Oregon, and Washington (Chen et al., 1995). Stripe rust is now firmly established in the western United States and has been especially severe in California and the Pacific Northwest, where the environment is most favorable for development of stripe rust epidemics. Since the major cultivars grown in the United States are susceptible, the disease has a high potential for causing major losses.

Use of resistant cultivars has been the most economical and effective method of controlling stripe rust of wheat and is potentially the most economical and effective method for control of barley stripe rust. Identification of genes for resistance and knowledge of their genetics are essential for effective development of resistant cultivars. Chen et al. (1995) reported that barley genotypes 'PI 548708', 'PI 548734', 'PI 548747', 'BBA 2890', 'Abyssinian 14', 'Grannelose Zweizeilige', 'Stauffers Obersulzer' were resistant to all of the races of P. s. hordei that have been detected in the United States and that 'Heils Franken', 'Emir', 'Astrix', 'Hiproly', 'Varunda', 'Trumpf', 'Mazurka', 'Bigo', 'Cambrinus', 'BBA 809', and 'I 5' were resistant to some races, i.e. they have differential reactions to the races. Chen and Line (1999) reported that PI 548708, PI 548734, PI 548747, Abyssinian 14, I 5, Stauffers Obersulzer, Heils Franken, Emir, Astrix, Hiproly, Varunda, and Trumpf each had two genes; and BBA2890, Grannelose Zweizeilige, Mazurka, Bigo, Cambrinus, and BBA 809 each had a single gene for resistance to stripe rust. The objectives of this study were to determine what genes are common for specific genotypes and to determine the relationships and interactions among the genes in the 18 barley genotypes.

Materials and methods

The 18 resistant barley genotypes used in this study plus susceptible 'Steptoe' and 'Topper' are listed in Table 1 along with their reactions to selected races of P. s. hordei. In the greenhouse, all possible crosses without their reciprocals were made among all 18 resistant genotypes. For each cross, at least two crossed heads were made using different plants of the genotypes as the parents. About five F₁ seeds from each single crossed head were grown in the field to obtain F₂ seeds. F₂ seeds from different individual F₁ plants were threshed and used separately in later tests.

To evaluate the plants for resistance, seedlings were inoculated uniformly at the two-leaf stage with urediniospores of a specific race, placed in a dew chamber at 10^o C for 24 hours, and then moved to a temperature controlled chamber with a diurnal temperature cycle that gradually changed from 4^o C at 2 AM to 20^o C at 2 PM and back to 4^o C at 2 AM. The light period consisted of daylight supplemented with metal halide lights to extend the photoperiod to 16 hours. North American races PSH-1, PSH-10, PSH-13, and PSH-20 of P. s. hordei (Chen et al. 1995; Line and Chen, 1996) were used to test the seedlings of the crosses.

Infection type (IT) data were recorded 18-22 days after inoculation according to the 0-9 scale described by Line et al. (1974). Infection types 0 - 3 were classified as resistant, infection types 4 - 6 were classified as intermediate, and infection types 7 - 9 were classified as susceptible. Chi-square tests were used to determine the goodness of fit of the segregation ratios.

Results and Discussion

Infection types produced by the races of P. s. hordei on the barley genotypes are listed in Table 1. The first six genotypes were resistant to all races and the remaining 12 genotypes were resistant to some races detected so far in the North America. Independent, linkage, and allelic relationships of genes in the 18 genotypes were determined based on 217 tests of F₂ seedlings of over 150 crosses.

BBA 2890, Bigo, Abyssinian 14, I 5, and Cambrinus. Barley genotypes BBA 2890, Bigo, Abyssinian 14, I 5, and Cambrinus have been previously studied using European isolates of P. s. striiformis (Johnson, 1968; Nover and Scholz, 1969). Nover and Scholz (1969) reported that BBA 2890, Bigo, and Abyssinia 14 had resistant alleles at the same locus, which they designated as yr. They designated a gene in I 5 as yr3. Johnson (1968) designated a gene in Cambrinus as Yr4. Using US races, Chen and Line (1999) detected one gene in BBA 2890, Bigo, and Cambrinus and two genes in Abyssinian 14 and I 5. Based on F₂ segregation ratios in this study and race reactions in our previous studies (Chen et al. 1995; Line and Chen 1996), we found that the single gene in BBA 2890 was allelic to but different from a gene in Bigo; one of the Abyssinian 14 genes was linked to genes in BBA 2890, and Bigo; and the genes in I 5 and Cambrinus were different from the genes in BBA 2890, Bigo, and Abyssinian 14.

PI 548734, PI 548708, and PI 548747. Chen and Line (1999) reported that PI 548734, PI 548708, and PI 548747 had two genes for stripe rust resistance. In this study, we found that the three genotypes had a gene or genes the same as, allelic, or closely linked to each other. The three genotypes had a gene linked to one of the Abyssinian 14 genes. One of the genes in PI 548734 might be the same as the gene in BBA 2890 and closely linked to genes in PI 548708 and PI 548747. The three genotypes had a gene linked to the gene in Bigo. One of the two genes in PI 548734 was linked to one of the two genes in I 5.

Heils Franken, Astrix, Mazurka, and Trumpf. We reported two genes in Heils Franken, Astrix, and Trumpf and one gene in Mazurka (Chen and Line, 1999). The data of this study suggest that Heils Franken, Astrix, and Cambrinus have a gene in common. The gene in Mazurka might be allelic or closely linked to genes in PI 548708, PI 548734, PI 548747, and Trumpf. One of the Trumpf genes was linked to genes in BBA 2890, Bigo, PI 548708, PI 548734, and PI 548747.

BBA 809, Grannelose Zweizeilige, Emir, Hiproly, Varunda, and Stauffers Obersulzer. Chen and Line (1999) reported that BBA 809 and Grannelose Zweizeilige had a single gene and Emir, Hiproly, Varunda, and Stauffers Obersulzer had two genes for stripe rust resistance. The results of this study showed that the genes in these genotypes were different from and unlinked to each other and also different from and unlinked to all other genes.

Based on the results of this study, at least 26 of the 30 genes in the 18 genotypes are different. The provisional designations of the genes are listed in Table 2. The Yr gene symbols used in earlier studies with barley (Johnson, 1968; Nover and Scholz, 1969) can be confused with the Yr gene symbols used for designations of resistance genes in wheat to P. s. tritici, the wheat stripe rust pathogen. Therefore, we are using the Rps as the symbol to designate genes in barley for resistance to the barley stripe rust pathogen, P. s. hordei in order to provide a consistent terminology for designations of the barley genes for stripe rust resistance. The proposed Rps symbols are in agreement with Moseman's (1972) proposal of symbols for barley genes for disease resistance and with von Wettstein-Knowles who used Rps4 to replace Yr4 (von Wettstein-Knowles, 1992).

Except for Abed Binder 12, all of the barley genotypes that were studied by Nover and Scholz (1969) were also used in this study. For Bigo and BBA 2890, our results are consistent with the results of Nover and Scholz (1969); the genes in Bigo and BBA 2890 are at the same locus. However, the alleles in the two genotypes are not the same, because Bigo is susceptible to some races while BBA 2890 is resistant to all races of P. s. hordei that have been detected in North America (Chen et al., 1995; Line and Chen, 1996). Therefore, the gene in BBA 2890 is designated as rps1.a and the gene in Bigo is designated as rps1.b (Table 2). The results of our previous study (Chen and Line, 1999) and of this study show that Abyssinian 14 has two genes rather than the single gene reported by Nover and Scholz' (1969). Similar to Nover and Scholz's results, linkage or allelism was not found between the genes in I 5 and the genes in Bigo, BBA 2890, and Abyssinian 14. However, we found that I 5 had two genes, and one of them was linked to rpsPI548734 in PI 548734. Because we did not include some barley genotypes used in the study by Luthra and Chopra (1990), the relationships of the genes, 'yr5' to 'Yr11', with genes identified in this study were not determined.

Barley genotypes PI 548708, PI 548734, PI 548747, and Abyssinian 14, which originated from Ethiopia, are resistant to all races of P. s. hordei detected in the United States (Chen et al. 1995). These genes should be useful sources for developing barley cultivars with resistance to stripe rust. The results of this study are also useful in understanding the barley and stripe rust interactions and should lead to more effective control of the rust.

^a PI = plant introduction number, CIho = cultivar identification number of Hordeum.

^b The number of genes is based on Chen and Line (1999).

^c The 0-9 scale of infection types was based on Line et al. (1974). Infection types 0, 1, 2, and 3 were considered resistant; infection types 4, 5, and 6 were considered intermediate; and infection types 7, 8, and 9 were considered susceptible.

^d Some races produced infection type 2 and other races produced infection type 8 (Chen et al. 1995).

TABLE 2. The provisional Rps genes for resistance to Puccinia striiformis f. sp. hordei in barley genotypes

^a rps1, rps2, rps3, and Rps4 were previously named yr, yr2, yr3, and Yr4, respectively (Nover and Scholz, 1969; Johnson 1968).

^b The cultivar was not included in this study.

References

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von Wettstein-Knowles, P. 1992. Cloned and Mapped Genes: Current Status. Page 73-98 in P.R. Shewry ed. "Barley: Genetics, Biochemistry, Molecular Biology, and Biotechnology". CAB Int., Wallingord, U.K.