Theor Appl Genet DOI 10.1007/s00122-014-2330-y
Original Paper
Characterization of Sr9h, a wheat stem rust resistance allele effective to Ug99 Matthew N. Rouse · Jayaveeramuthu Nirmala · Yue Jin · Shiaoman Chao · Thomas G. Fetch Jr. · Zacharias A. Pretorius · Colin W. Hiebert
Received: 24 January 2014 / Accepted: 12 May 2014 © Springer-Verlag Berlin Heidelberg (outside the USA) 2014
Abstract Key message Wheat stem rust resistance gene SrWeb is an allele at the Sr9 locus that confers resistance to Ug99. Abstract Race TTKSK (Ug99) of Puccinia graminis f. sp. tritici, the causal fungus of stem rust, threatens global wheat production because of its broad virulence to current wheat cultivars. A recently identified Ug99 resistance gene from cultivar Webster, temporarily designated as SrWeb, mapped near the stem rust resistance gene locus Sr9. We determined that SrWeb is also present in Ug99 resistant cultivar Gabo 56 by comparative mapping and an allelism test. Analysis of resistance in a population segregating for both Sr9e and SrWeb demonstrated that SrWeb is an allele at the Sr9 locus, which subsequently was designated as Sr9h. Webster and Communicated by Evans Lagudah. M. N. Rouse (*) · J. Nirmala · Y. Jin Cereal Disease Laboratory, United States Department of Agriculture-Agricultural Research Service (USDA-ARS), 1551 Lindig Street, St. Paul, MN, USA e-mail: [email protected] M. N. Rouse · Y. Jin Department of Plant Pathology, University of Minnesota, 1991 Upper Buford Circle, 495 Borlaug Hall, St. Paul, MN 55108, USA S. Chao Biosciences Research Laboratory, USDA-ARS, 1605 Albrecht Blvd. N., Fargo, ND 58102, USA T. G. Fetch Jr. · C. W. Hiebert Cereal Research Centre, Agriculture and Agri-Food Canada, 195 Dafoe Road, Winnipeg, MB R3T 2M9, Canada Z. A. Pretorius Department of Plant Sciences, University of the Free State, Bloemfontein 9300, South Africa
Gabo 56 were susceptible to the Ug99-related race TTKSF+ from South Africa. Race TTKSF+ possesses unique virulence to uncharacterized Ug99 resistance in cultivar Matlabas. This result validated that resistance to Ug99 in Webster and Gabo 56 is conferred by the same gene: Sr9h. The emergence of pathogen virulence to several resistance genes that are effective to the original Ug99 race TTKSK, including Sr9h, suggests that resistance genes should be used in combinations in order to increase resistance durability.
Introduction Puccinia graminis Pers.:Pers f. sp. tritici Eriks. & E. Henn (Pgt) is the causal fungus of wheat stem rust, one of the most significant diseases of bread wheat (Triticum aestivum L.), durum wheat (T. turgidum var. durum), barley (Hordeum vulgare L.), and triticale (X Triticosecale Wittmack) (Leonard 2001; Roelfs et al. 1992). Wheat stem rust has become increasingly important since 1999 when an isolate of Pgt called Ug99 (race TTKSK; Jin et al. 2007, 2008) was shown to possess unique virulence to Sr31 in addition to virulence to the majority of wheat cultivars around the world (Jin and Singh 2006; Pretorius et al. 2000; Singh et al. 2008). Variants of race TTKSK were identified with additional virulence to wheat resistance genes Sr24 (Jin et al. 2008; Pretorius et al. 2010; Visser et al. 2011) and Sr36 (Jin et al. 2009). In 2010, a Pgt isolate collected in South Africa possessed virulence to winter wheat cultivar Matlabas (Pretorius et al. 2012). Further studies demonstrated that Matlabas displayed resistance to several Ug99 race group variants, but not to the isolate collected from Matlabas described as race TTKSF+. The spread of race TTKSK and diverse variants throughout Africa and the Middle East (Nazari et al. 2009) demonstrated the need for identifying and utilizing multiple
13
Ug99 resistance genes. There are at least 31 wheat stem rust resistance (Sr) genes with diverse origins that confer resistance to Ug99: Sr2, Sr13, Sr21, Sr22, Sr24, Sr25, Sr26, Sr27, Sr28, Sr32, Sr33, Sr35, Sr36, Sr37, Sr39, Sr40, Sr42, Sr44, Sr45, Sr46, Sr47, Sr51, Sr52, Sr53, Sr57(Lr34), SrTA10171, SrTA10187, SrTA1662, SrTmp, SrWeb, Sr1RSAmigo (Faris et al. 2008; Ghazvini et al. 2012; Hiebert et al. 2010; Kolmer et al. 2011; Jin and Singh 2006; Jin et al. 2007; Liu et al. 2011a, b; Olson et al. 2013a, b; Qi et al. 2011; Rouse et al. 2011a; Rouse and Jin 2011; Singh et al. 2013). These 31 genes vary in their level of effectiveness to Ug99 and race specificity within the Ug99 race group and to diverse Pgt races. The five genes that originate from T. aestivum, Sr28, Sr42, Sr57, SrTmp, and SrWeb, are valuable resources for Ug99 resistance because they are not located on introgressed chromatin from alien species with possible linkage drag. Stem rust resistance genes Sr9, Sr16, Sr28, and Sr47 have been located on chromosome arm 2BL. In addition, Ug99 resistance gene SrWeb was previously mapped to chromosome arm 2BL near the Sr9 locus (Hiebert et al. 2010; Tsilo et al. 2007). There are six characterized alleles at the Sr9 locus, and each demonstrates unique race specificities to Pgt races: Sr9a, Sr9b, Sr9d, Sr9e, Sr9f, and Sr9g (Green et al. 1960; Knott 1966; Loegering 1975; McIntosh and Luig 1973). The gene designation Sr9c was originally reserved for a gene that was subsequently designated as Sr36 on chromosome arm 2BS (McIntosh et al. 1995). The previously characterized Sr9 alleles and Sr16 are ineffective to Ug99, whereas Sr28 and Sr47 confer resistance (Jin et al. 2007). Molecular markers linked to Sr28 were identified on chromosome arm 2BL (Rouse et al. 2012). Molecular markers linked to Sr47 and a shortened Aegilops speltoides Tausch introgression possessing Sr47 were recently derived (Klindworth et al. 2012). The potential allelism of SrWeb and other stem rust resistance genes on chromosome arm 2BL has not been tested. We observed seedling resistance to Pgt race TTKSK in 1956 Rockefeller Foundation cultivar Gabo 56. The pedigree of Gabo 56 is Timstein/Kenya 58//Gabo (CI 14035). Previous studies determined that Timstein and Gabo possessed stem rust resistance gene Sr11 (Knott and Anderson 1956). A second stem rust resistance gene was initially described in Timstein and Gabo (Knott and Anderson 1956), but subsequent studies demonstrated that abnormal transmission of gametes and Sr11 explained the observed segregation of resistance (Luig 1960; Sears and Loegering 1961). Watson and Stewart (1956) suggested that Timstein and Gabo are both derived from the cross Bobin W39*2/Gaza based on observed race specificity of resistance to stem and leaf rust and dissimilarity between resistance in Timstein and that of its originally proposed parents
13
Theor Appl Genet
Steinwedel (CI 1702) and T. timopheevi Zhuk. (Boasso and Levine 1951; Levine et al. 1951). Kenya 58 was demonstrated to possess Sr6 and Sr7a (Knott and Anderson 1956; Loegering and Sears 1966). Genes Sr6, Sr7a, and Sr11 are all ineffective to Ug99 race TTKSK (Jin et al. 2007). The genetics and source of Ug99 resistance in Gabo 56 were not known. Our objectives were (1) to determine the genetics of resistance to Ug99 in cultivar Gabo 56 and (2) to determine the allelic relationship between SrWeb and other stem rust resistance genes on chromosome arm 2BL.
Materials and methods Wheat germplasm We derived a total of five wheat populations from six parental lines. We crossed cultivar Gabo 56 (accession CI 14035, from the United States Department of Agriculture National Small Grains Collection) with susceptible cultivar Chinese Spring in order to characterize the stem rust resistance in Gabo 56. A total of 104 F2:3 families were derived. Phenotyping the F2:3 families with race TTKSK and mapping the resistance with molecular markers indicated that Gabo 56 resistance could be conferred by SrWeb (see “Results”). In order to test this hypothesis, we crossed SrWeb-containing wheat line Webster obtained from the Cereal Research Centre (RL6201; Agriculture and AgriFood Canada) with Gabo 56 in order to conduct an allelism test. A total of 356 doubled haploid lines were derived from this population at the Cereal Research Centre using a maize pollination method (Thomas et al. 1997). To test for the allelic relationship between the resistance gene in Gabo 56 and other resistance genes on chromosome arm 2BL, Gabo 56 was crossed to Sr9e line Vernstein (Jin et al. 2007) and also Sr28 line SD 1691 (CI 12499; Rouse et al. 2012). For the Gabo 56/Vernstein population, 347 F2:3 families were derived. A total of 82 F2:3 families were utilized from a previously derived SD 1691/Gabo 56 population (Rouse et al. 2012). A single F3 plant from a SD 1691/Gabo 56 F2:3 family that was fixed for both SrWeb and Sr28 (see “Results”) was increased for two subsequent generations and deposited at the USDA-ARS National Small Grains Collection as CDL001 (PI 670015). To validate the presence of both SrWeb and Sr28 in CDL001, we derived a total of 292 F2 seeds from CDL001/LMPG-6. Wheat line LMPG-6 is a stem rust susceptible hard red spring wheat (Knott 1990). We obtained the parents of Gabo 56, Timstein (CI 12347), Kenya 58 (CI 12471), and Gabo (CI 12795), to assess the origin of resistance to Ug99 in Gabo 56.
Theor Appl Genet
Stem rust phenotyping Procedures in inoculation, incubation, and disease assessment were followed as described previously (Rouse et al. 2011b). Infection types (ITs) were classified as in Stakman et al. (1962). Infection types ‘0’ to ‘2’ were considered low infection types indicating host resistance, whereas ITs ‘3’ to ‘4’ were considered high infection types indicating host susceptibility. For each seedling experiment, we inoculated the population, the parents of the population, and the International stem rust differential set (Roelfs and Martens 1988; Jin et al. 2008). For F2:3 families, 20–25 plants from each family were screened. Five plants for each DH line were inoculated. The phenotypes of the F2:3 families were used to classify the genotypes of the parent F2 plants as homozygous resistant, homozygous susceptible, or heterozygous in reaction to the Pgt race tested. For F2:3 families with
Original Paper
Characterization of Sr9h, a wheat stem rust resistance allele effective to Ug99 Matthew N. Rouse · Jayaveeramuthu Nirmala · Yue Jin · Shiaoman Chao · Thomas G. Fetch Jr. · Zacharias A. Pretorius · Colin W. Hiebert
Received: 24 January 2014 / Accepted: 12 May 2014 © Springer-Verlag Berlin Heidelberg (outside the USA) 2014
Abstract Key message Wheat stem rust resistance gene SrWeb is an allele at the Sr9 locus that confers resistance to Ug99. Abstract Race TTKSK (Ug99) of Puccinia graminis f. sp. tritici, the causal fungus of stem rust, threatens global wheat production because of its broad virulence to current wheat cultivars. A recently identified Ug99 resistance gene from cultivar Webster, temporarily designated as SrWeb, mapped near the stem rust resistance gene locus Sr9. We determined that SrWeb is also present in Ug99 resistant cultivar Gabo 56 by comparative mapping and an allelism test. Analysis of resistance in a population segregating for both Sr9e and SrWeb demonstrated that SrWeb is an allele at the Sr9 locus, which subsequently was designated as Sr9h. Webster and Communicated by Evans Lagudah. M. N. Rouse (*) · J. Nirmala · Y. Jin Cereal Disease Laboratory, United States Department of Agriculture-Agricultural Research Service (USDA-ARS), 1551 Lindig Street, St. Paul, MN, USA e-mail: [email protected] M. N. Rouse · Y. Jin Department of Plant Pathology, University of Minnesota, 1991 Upper Buford Circle, 495 Borlaug Hall, St. Paul, MN 55108, USA S. Chao Biosciences Research Laboratory, USDA-ARS, 1605 Albrecht Blvd. N., Fargo, ND 58102, USA T. G. Fetch Jr. · C. W. Hiebert Cereal Research Centre, Agriculture and Agri-Food Canada, 195 Dafoe Road, Winnipeg, MB R3T 2M9, Canada Z. A. Pretorius Department of Plant Sciences, University of the Free State, Bloemfontein 9300, South Africa
Gabo 56 were susceptible to the Ug99-related race TTKSF+ from South Africa. Race TTKSF+ possesses unique virulence to uncharacterized Ug99 resistance in cultivar Matlabas. This result validated that resistance to Ug99 in Webster and Gabo 56 is conferred by the same gene: Sr9h. The emergence of pathogen virulence to several resistance genes that are effective to the original Ug99 race TTKSK, including Sr9h, suggests that resistance genes should be used in combinations in order to increase resistance durability.
Introduction Puccinia graminis Pers.:Pers f. sp. tritici Eriks. & E. Henn (Pgt) is the causal fungus of wheat stem rust, one of the most significant diseases of bread wheat (Triticum aestivum L.), durum wheat (T. turgidum var. durum), barley (Hordeum vulgare L.), and triticale (X Triticosecale Wittmack) (Leonard 2001; Roelfs et al. 1992). Wheat stem rust has become increasingly important since 1999 when an isolate of Pgt called Ug99 (race TTKSK; Jin et al. 2007, 2008) was shown to possess unique virulence to Sr31 in addition to virulence to the majority of wheat cultivars around the world (Jin and Singh 2006; Pretorius et al. 2000; Singh et al. 2008). Variants of race TTKSK were identified with additional virulence to wheat resistance genes Sr24 (Jin et al. 2008; Pretorius et al. 2010; Visser et al. 2011) and Sr36 (Jin et al. 2009). In 2010, a Pgt isolate collected in South Africa possessed virulence to winter wheat cultivar Matlabas (Pretorius et al. 2012). Further studies demonstrated that Matlabas displayed resistance to several Ug99 race group variants, but not to the isolate collected from Matlabas described as race TTKSF+. The spread of race TTKSK and diverse variants throughout Africa and the Middle East (Nazari et al. 2009) demonstrated the need for identifying and utilizing multiple
13
Ug99 resistance genes. There are at least 31 wheat stem rust resistance (Sr) genes with diverse origins that confer resistance to Ug99: Sr2, Sr13, Sr21, Sr22, Sr24, Sr25, Sr26, Sr27, Sr28, Sr32, Sr33, Sr35, Sr36, Sr37, Sr39, Sr40, Sr42, Sr44, Sr45, Sr46, Sr47, Sr51, Sr52, Sr53, Sr57(Lr34), SrTA10171, SrTA10187, SrTA1662, SrTmp, SrWeb, Sr1RSAmigo (Faris et al. 2008; Ghazvini et al. 2012; Hiebert et al. 2010; Kolmer et al. 2011; Jin and Singh 2006; Jin et al. 2007; Liu et al. 2011a, b; Olson et al. 2013a, b; Qi et al. 2011; Rouse et al. 2011a; Rouse and Jin 2011; Singh et al. 2013). These 31 genes vary in their level of effectiveness to Ug99 and race specificity within the Ug99 race group and to diverse Pgt races. The five genes that originate from T. aestivum, Sr28, Sr42, Sr57, SrTmp, and SrWeb, are valuable resources for Ug99 resistance because they are not located on introgressed chromatin from alien species with possible linkage drag. Stem rust resistance genes Sr9, Sr16, Sr28, and Sr47 have been located on chromosome arm 2BL. In addition, Ug99 resistance gene SrWeb was previously mapped to chromosome arm 2BL near the Sr9 locus (Hiebert et al. 2010; Tsilo et al. 2007). There are six characterized alleles at the Sr9 locus, and each demonstrates unique race specificities to Pgt races: Sr9a, Sr9b, Sr9d, Sr9e, Sr9f, and Sr9g (Green et al. 1960; Knott 1966; Loegering 1975; McIntosh and Luig 1973). The gene designation Sr9c was originally reserved for a gene that was subsequently designated as Sr36 on chromosome arm 2BS (McIntosh et al. 1995). The previously characterized Sr9 alleles and Sr16 are ineffective to Ug99, whereas Sr28 and Sr47 confer resistance (Jin et al. 2007). Molecular markers linked to Sr28 were identified on chromosome arm 2BL (Rouse et al. 2012). Molecular markers linked to Sr47 and a shortened Aegilops speltoides Tausch introgression possessing Sr47 were recently derived (Klindworth et al. 2012). The potential allelism of SrWeb and other stem rust resistance genes on chromosome arm 2BL has not been tested. We observed seedling resistance to Pgt race TTKSK in 1956 Rockefeller Foundation cultivar Gabo 56. The pedigree of Gabo 56 is Timstein/Kenya 58//Gabo (CI 14035). Previous studies determined that Timstein and Gabo possessed stem rust resistance gene Sr11 (Knott and Anderson 1956). A second stem rust resistance gene was initially described in Timstein and Gabo (Knott and Anderson 1956), but subsequent studies demonstrated that abnormal transmission of gametes and Sr11 explained the observed segregation of resistance (Luig 1960; Sears and Loegering 1961). Watson and Stewart (1956) suggested that Timstein and Gabo are both derived from the cross Bobin W39*2/Gaza based on observed race specificity of resistance to stem and leaf rust and dissimilarity between resistance in Timstein and that of its originally proposed parents
13
Theor Appl Genet
Steinwedel (CI 1702) and T. timopheevi Zhuk. (Boasso and Levine 1951; Levine et al. 1951). Kenya 58 was demonstrated to possess Sr6 and Sr7a (Knott and Anderson 1956; Loegering and Sears 1966). Genes Sr6, Sr7a, and Sr11 are all ineffective to Ug99 race TTKSK (Jin et al. 2007). The genetics and source of Ug99 resistance in Gabo 56 were not known. Our objectives were (1) to determine the genetics of resistance to Ug99 in cultivar Gabo 56 and (2) to determine the allelic relationship between SrWeb and other stem rust resistance genes on chromosome arm 2BL.
Materials and methods Wheat germplasm We derived a total of five wheat populations from six parental lines. We crossed cultivar Gabo 56 (accession CI 14035, from the United States Department of Agriculture National Small Grains Collection) with susceptible cultivar Chinese Spring in order to characterize the stem rust resistance in Gabo 56. A total of 104 F2:3 families were derived. Phenotyping the F2:3 families with race TTKSK and mapping the resistance with molecular markers indicated that Gabo 56 resistance could be conferred by SrWeb (see “Results”). In order to test this hypothesis, we crossed SrWeb-containing wheat line Webster obtained from the Cereal Research Centre (RL6201; Agriculture and AgriFood Canada) with Gabo 56 in order to conduct an allelism test. A total of 356 doubled haploid lines were derived from this population at the Cereal Research Centre using a maize pollination method (Thomas et al. 1997). To test for the allelic relationship between the resistance gene in Gabo 56 and other resistance genes on chromosome arm 2BL, Gabo 56 was crossed to Sr9e line Vernstein (Jin et al. 2007) and also Sr28 line SD 1691 (CI 12499; Rouse et al. 2012). For the Gabo 56/Vernstein population, 347 F2:3 families were derived. A total of 82 F2:3 families were utilized from a previously derived SD 1691/Gabo 56 population (Rouse et al. 2012). A single F3 plant from a SD 1691/Gabo 56 F2:3 family that was fixed for both SrWeb and Sr28 (see “Results”) was increased for two subsequent generations and deposited at the USDA-ARS National Small Grains Collection as CDL001 (PI 670015). To validate the presence of both SrWeb and Sr28 in CDL001, we derived a total of 292 F2 seeds from CDL001/LMPG-6. Wheat line LMPG-6 is a stem rust susceptible hard red spring wheat (Knott 1990). We obtained the parents of Gabo 56, Timstein (CI 12347), Kenya 58 (CI 12471), and Gabo (CI 12795), to assess the origin of resistance to Ug99 in Gabo 56.
Theor Appl Genet
Stem rust phenotyping Procedures in inoculation, incubation, and disease assessment were followed as described previously (Rouse et al. 2011b). Infection types (ITs) were classified as in Stakman et al. (1962). Infection types ‘0’ to ‘2’ were considered low infection types indicating host resistance, whereas ITs ‘3’ to ‘4’ were considered high infection types indicating host susceptibility. For each seedling experiment, we inoculated the population, the parents of the population, and the International stem rust differential set (Roelfs and Martens 1988; Jin et al. 2008). For F2:3 families, 20–25 plants from each family were screened. Five plants for each DH line were inoculated. The phenotypes of the F2:3 families were used to classify the genotypes of the parent F2 plants as homozygous resistant, homozygous susceptible, or heterozygous in reaction to the Pgt race tested. For F2:3 families with
