Mapping and characterization of the recessive leaf rust resistance gene Lr83 on wheat chromosome arm 1DS.

KEY MESSAGE: The leaf rust resistance gene in Thatcher wheat derivative 78-1 was mapped to chromosome 1DS with SNP markers and designated as Lr83. 'Thatcher' wheat near isogenic line RL6149, a putative derivative of Triticum dicoccoides, was previously determined to carry leaf rust resistance gene Lr64 on chromosome arm 6AL and a second gene temporarily named LrX on chromosome arm 1DS. The objective of this study was to map and characterize LrX in a population of recombinant inbred lines (RILs) that segregated for a single gene. Thatcher line 78-1 with LrX was crossed with Thatcher and individual F2 seedlings and F6 RILs were evaluated for leaf rust response. The 208 F2 plants segregated for a single recessive gene and 148 F6 lines for a single gene. The RILs and parents were characterized by genotyping by sequencing (GBS). Six GBS markers and five Kompetitive Allele-Specific PCR (KASP) markers were used to map LrX on the distal region of chromosome arm 1DS. LrX was 1 centiMorgan (cM) proximal to marker K-IWB38437 and 0.4 cM distal to GBS marker 1D_9037138. Line 78-1 was crossed with Thatcher wheat lines with Lr21, Lr42, and Lr60 for allelism tests. LrX mapped 19.49 cM from Lr21 and 11.93 cM from Lr42. In the cross of line 78-1 with the Thatcher line with Lr60, one recombinant in 1,003 F2 plants was found. LrX and Lr60 are at tightly linked loci on the distal region of chromosome arm 1DS. The gene in line 78-1 was designated as Lr83. Cytological examination of RL6149 provided no evidence of transfer of a chromosome segment of an A- or B-genome chromosome to chromosome 1D.

Genotype Groups of the Wheat Leaf Rust Fungus Puccinia triticina in the United States as Determined by Genotyping by Sequencing.

Wheat leaf rust caused by Puccinia triticina is a widespread disease of wheat in the United States and worldwide. Populations of P. triticina are characterized by virulence phenotypes that change rapidly because of selection by wheat cultivars with leaf rust resistance genes. The objective of this study was to genotype collections of P. triticina from 2011 to 2018 in the United States using restriction site-associated genotyping by sequencing (GBS) to determine if recently identified new virulence phenotypes belong to established genotype groups or to groups previously not detected. A total of 158 isolates were phenotyped for virulence on 20 lines of Thatcher wheat that are isogenic for leaf rust resistance genes and also genotyped for single nucleotide polymorphism. Eight distinct groups of P. triticina genotypes from common wheat were described based on coancestry, nucleotide divergence, and principal coordinate plots. A separate genotype group had isolates with virulence to durum wheat. Isolates within groups had similar virulence phenotypes, and the overall population had high levels of heterozygosity and high levels of linkage disequilibria, which were all indicators of clonality. Two new genotype groups were described, thereby raising the possibility of new introductions of P. triticina; however, genotypes in these groups may have also originated from somatic nuclear exchange and recombination. A genome-wide association study detected 19 single nucleotide polymorphisms that were highly associated with virulence to 11 resistance genes in the Thatcher near-isogenic lines.

Adult Plant Leaf Rust Resistance in AC Taber Wheat Maps to Chromosomes 2BS and 3BS.

AC Taber is a hard red spring wheat cultivar that has had long-lasting resistance to the leaf rust fungus Puccinia triticina. The objective of this study was to determine the chromosome location of the leaf rust resistance genes in AC Taber. The leaf rust-susceptible cultivar Thatcher was crossed with AC Taber to develop an F6 recombinant inbred line (RIL) population. The RILs and parents were evaluated for segregation of leaf rust resistance in five field plot tests and in two seedling tests to race BBBDB of P. triticina. A genetic map of the RIL population was developed using 90,000 single nucleotide polymorphism markers with the Illumina Infinium iSelect 90K wheat bead array. Quantitative trait loci (QTLs) with significant effects for lower leaf rust severity in the field plot tests were found on chromosomes 2BS and 3BS. The same QTLs also had significant effects for lower infection type in seedlings to leaf rust race BBBDB. The gene on 2BS was the adult plant resistance gene Lr13, and the gene on 3BS mapped to the same region as the adult plant resistance gene Lr74 and other QTLs for leaf rust resistance. Kompetitive allele-specific PCR assay markers linked to the 2BS and 3BS regions were developed and should be useful for marker-based selection of these genes.

Endemic and panglobal genetic groups, and divergence of host-associated forms in worldwide collections of the wheat leaf rust fungus Puccinia triticina as determined by genotyping by sequencing.

The wheat leaf rust fungus, Puccinia triticina, is found in the major wheat growing regions of the world and is a leading cause of yield loss in wheat. Populations of P. triticina are highly variable for virulence to resistance genes in wheat and adapt quickly to resistance genes in wheat cultivars. The objectives of this study were to determine the genetic relatedness of worldwide collections of P. triticina using restriction site associated genotyping by sequencing. A total of 558 isolates of P. triticina from wheat producing regions in North America, South America, Europe, the Middle East, Ethiopia, Russia, Pakistan, Central Asia, China, New Zealand, and South Africa were characterized at 6745 single nucleotide loci. Isolates were also tested for virulence to 20 near-isogenic lines that differ for leaf rust resistance genes. Populations that were geographically proximal were also more closely related for genotypes. In addition, groups of isolates within regions that varied for genotype were similar to groups from other regions, which indicated past and recent migration across regions. Isolates from tetraploid durum wheat in five different regions were highly related with distinct genotypes compared to isolates from hexaploid common wheat. Based on a molecular clock, isolates from durum wheat found only in Ethiopia were the first to diverge from a common ancestor form of P. triticina that is found on the wild wheat relative Aegilops speltoides, followed by the divergence of isolates found worldwide that are virulent to durum wheat, and then by isolates found on common wheat.

Thatcher wheat line RL6149 carries Lr64 and a second leaf rust resistance gene on chromosome 1DS.

KEY MESSAGE: The leaf rust resistance gene Lr64 in the Thatcher wheat RL6149 was mapped to chromosome 6AL with SNP and KASP markers and a second leaf rust resistance gene was mapped to chromosome 1DS. RL6149, a near-isogenic line of Thatcher wheat, carries leaf rust resistance gene Lr64 on chromosome arm 6AL. The objective of this study was to develop molecular markers that can be easily used to select wheat lines with Lr64. RL6149 was crossed with Thatcher and F2 plants derived from a single F1 plant were advanced to F6 lines by single seed descent. The 100 F7 recombinant inbred lines (RIL) were inoculated with two races of P.triticina that differed widely for virulence in order to identify resistant and susceptible RIL. Thirty RIL that differed for resistance and the parental lines were genotyped with the 90 K Infinium iSelect single nucleotide polymorphism (SNP) array to find closely linked markers with Lr64. Seven linked SNPs on chromosome arm 6AL were converted into Kompetitive Allele Specific PCR (KASP) markers that were genotyped on the 100 RIL. A genetic linkage map for the seven KASP markers spanned 19.1 cM on chromosome arm 6AL. KASP marker K-IWB59855 was tightly linked to Lr64. A second unexpected gene for leaf rust resistance also segregated in the F7 lines. Four KASP markers that spanned 18.6 cM located the gene on chromosome 1DS. The KASP marker K-IWB38437 was tightly linked to the second leaf rust resistance gene.

Virulence of Puccinia triticina, the Wheat Leaf Rust Fungus, in the United States in 2017.

Samples of wheat leaves infected with the leaf rust fungus, Puccinia triticina, were obtained in 2017 from agricultural experiment station plots, demonstration plots, and farm fields in the Great Plains, the Ohio Valley, the southeastern states, California, and Washington in order to determine the prevalent virulence phenotypes present in the United States. A total of 65 virulence phenotypes were identified among the 469 single uredinial isolates that were tested on 20 near-isogenic lines of Thatcher wheat that differ for leaf rust resistance genes. Virulence phenotypes MBTNB at 11.3% of the overall population, and MCTNB at 7.0%, were the first and third most common phenotypes. Both phenotypes were found mostly in the southeastern states and Ohio Valley region. Phenotype TFTSB at 10.9% was the second most common phenotype and was found mostly in southern Texas. Virulence to leaf rust resistance gene Lr39, which is present in hard red winter wheat cultivars, was highest in the Great Plains region. Virulence to Lr11 and Lr18, which are present in soft red winter wheat cultivars, was highest in the southeastern states and Ohio Valley region. Virulence to Lr21, which is present in hard red spring wheat cultivars, was highest in the northern Great Plains region. The predominate P. triticina phenotypes from the soft red winter wheat regions of the southeastern states and Ohio Valley area differed from those in the hard red winter and hard red spring wheat areas of the Great Plains region. Collections from Washington had unique virulence phenotypes that had not been previously detected.

Multilocus Genotypes of the Wheat Leaf Rust Fungus Puccinia triticina in Worldwide Regions Indicate Past and Current Long-Distance Migration.

Many plant pathogenic fungi have a global distribution across diverse ecological zones and agricultural production systems. Puccinia triticina, the wheat leaf rust fungus, is a major pathogen in many wheat production areas of the world. The objective of this research was to determine the genetic relatedness of P. triticina in different worldwide regions. A total of 831 single-uredinial isolates collected from 11 regions were characterized for multilocus genotype at 23 simple sequence repeat loci and for virulence to 20 lines of wheat with single genes for leaf rust resistance. A total of 424 multilocus genotypes and 497 virulence phenotypes were found. All populations had high heterozygosity and significant correlation between virulence and molecular variation, which indicated clonal reproduction. The populations from North America and South America, Central Asia and Russia, and the Middle East and Europe were closely related for multilocus genotypes and many individual isolates from other continental regions were closely related. Twenty-seven multilocus genotypes were found in more than one continental region, and 13 of these had isolates with identical virulence phenotypes. The wide geographic distribution of identical and highly related multilocus genotypes of P. triticina indicated past and more recent migration events facilitated by the spread of clonally produced urediniospores.

A Backcross Line of Thatcher Wheat with Adult Plant Leaf Rust Resistance Derived from Duster Wheat has Lr46 and Lr77.

The widely grown hard red winter wheat cultivar Duster released in 2006 has remained highly resistant to leaf rust caused by Puccinia triticina in the southern Great Plains of the United States. In contrast, many of the winter wheat cultivars in this region are susceptible to leaf rust. The goal of this study was to identify the number and chromosome location of leaf rust resistance genes in a line of Thatcher*2/Duster wheat that was selected for adult plant leaf rust resistance. The Thatcher*2/Duster line was crossed with Thatcher (Tc) and a recombinant line inbred line (RIL) population was advanced to the F6 generation by single-seed descent. The parents and RIL population were phenotyped for leaf rust resistance in three field plot tests and in an adult plant greenhouse test. Single-nucleotide polymorphism (SNP) markers derived from the Illumina Infinium iSelect 90K wheat SNP array, kompetitive allele-specific polymerase chain reaction assays on chromosome 3BL, and a sequence tagged site (STS) marker on chromosome 1BL were used to construct a genetic map of the RIL population. The STS marker csLV46G22 that is linked with resistance gene Lr46 on chromosome 1BL, and SNP marker IWB10344 that is linked with Lr77 on chromosome 3BL, were significantly associated with lower leaf rust severity. Duster has at least three adult plant resistance genes for leaf rust resistance because it was previously determined to also have the adult plant resistance gene Lr34. Duster is a valuable source of durable leaf rust resistance for hard red winter wheat improvement in the Great Plains region.

Adult Plant Leaf Rust Resistance Derived from Toropi Wheat is Conditioned by Lr78 and Three Minor QTL.

Leaf rust caused by Puccinia triticina is an important disease of wheat in many regions worldwide. Durable or long-lasting leaf rust resistance has been difficult to achieve because populations of P. triticina are highly variable for virulence to race-specific resistance genes, and respond to selection by resistance genes in released wheat cultivars. The wheat cultivar Toropi, developed and grown in Brazil, was noted to have long-lasting leaf rust resistance that was effective only in adult plants. The objectives of this study were to determine the chromosome location of the leaf rust resistance genes derived from Toropi in two populations of recombinant inbred lines in a partial Thatcher wheat background. In the first population, a single gene with major effects on chromosome 5DS that mapped 2.2 centimorgans distal to IWA6289, strongly reduced leaf rust severity in all 3 years of field plot tests. This gene for adult plant leaf rust resistance was designated as Lr78. In the second population, quantitative trait loci (QTL) with small effects on chromosomes 1BL, 3BS, and 4BS were found. These QTL expressed inconsistently over 4 years of field plot tests. The adult plant leaf rust resistance derived from Toropi involved a complex combination of QTL with large and small effects.

Physiologic Specialization of Puccinia triticina on Wheat in the United States in 2016.

Leaves of wheat infected with the leaf rust fungus Puccinia triticina were obtained from farm fields and breeding plots at experimental stations in the Great Plains, Ohio River Valley, and southeastern states in 2016 in order to identify virulence phenotypes prevalent in the United States in different wheat-growing regions. In total, 496 single uredinial isolates derived from the leaf rust collections were tested for virulence to 20 lines of Thatcher wheat that differ for single leaf rust resistance genes. In total, 71 virulence phenotypes were described in the United States in 2016. The three most common virulence phenotypes across the United States were MBTNB, MBDSD, and TNBJJ. Phenotype MBTNB is virulent to Lr11, and was most common in the soft red winter wheat region of the southeastern states and Ohio Valley. Phenotype MBDSD is virulent to Lr17 and Lr39, and was most common in the hard red winter wheat area of the southern Great Plains. Phenotype TNBJJ is virulent to Lr24 and Lr39, which are present in the hard red winter wheat cultivars. The P. triticina population in the United States was characterized by two major regional groups of virulence phenotypes in the Great Plains region where hard red winter and spring wheat cultivars are grown, and in the southeastern states and Ohio Valley region where soft red winter wheat cultivars are grown. Isolates from New York State differed the most for virulence compared with the other two major regions.

Genetic Differentiation of the Wheat Leaf Rust Fungus Puccinia triticina in Pakistan and Genetic Relationship to Other Worldwide Populations.

Collections of Puccinia triticina, the wheat leaf rust pathogen, were obtained from Pakistan in 2008, 2010, 2011, 2013, and 2014. Collections were also obtained from Bhutan in 2013. Single uredinial isolates were derived and tested for virulence phenotype to 20 lines of Thatcher wheat that differ for single leaf rust resistance genes, and for molecular genotype with 23 simple-sequence repeat (SSR) primers. Twenty-four virulence phenotypes were described among the 89 isolates tested for virulence. None of the isolates had virulence to Thatcher lines with Lr9, Lr24, or Lr18. Virulence to most of the other Thatcher lines was over 50%. The two most common virulence phenotypes, FHPSQ and KHPQQ, had virulence to Lr16, Lr17, and Lr26. Twenty-seven SSR genotypes were found among the 38 isolates tested for molecular variation. The SSR genotypes had high levels of observed heterozygosity and significant correlation with virulence phenotype, which indicated clonal reproduction. Cluster analysis and principal component plots indicated three groups of SSR genotypes that also varied significantly for virulence. Isolates with MBDSS and MCDSS virulence phenotypes from Pakistan and Bhutan were highly related for SSR genotype and virulence to isolates from Turkey, Europe, Central Asia, the Middle East, North America and South America, indicating the possible migration of the rust fungus between continental regions.

Physiologic Specialization of Puccinia triticina on Wheat in the United States in 2015.

Leaves of wheat infected with the leaf rust fungus, Puccinia triticina, were obtained from farm fields and breeding plots at experimental stations in the Great Plains, Ohio River Valley, and southeastern states in 2015 in order to identify virulence phenotypes prevalent in the United States in different wheat growing regions. A total of 526 single uredinial isolates derived from the leaf rust collections were tested for virulence to 20 lines of Thatcher wheat that differ for single leaf rust resistance genes. A total of 60 virulence phenotypes were described in the United States in 2015. The three most common virulence phenotypes across the United States were MBDSD, MBTNB, and TBBGS. Phenotype MBDSD is virulent to Lr17, Lr37, and Lr39, and was most common in the hard red winter wheat area of the southern Great Plains. Phenotype MBTNB is virulent to Lr11, and was most common in the soft red winter wheat region of the southeastern states and Ohio Valley. Phenotype TBBGS is virulent to Lr39, which is present in the hard red winter wheat cultivars, and Lr21, which is present in the hard red spring wheat cultivars. The P. triticina population in the United States was characterized by two major regional groups of virulence phenotypes in the Great Plains region where hard red winter and spring wheat cultivars are grown, and in the southeastern states and Ohio Valley region where soft red winter wheat cultivars are grown.

Genetically Divergent Types of the Wheat Leaf Fungus Puccinia triticina in Ethiopia, a Center of Tetraploid Wheat Diversity.

Collections of Puccinia triticina, the wheat leaf rust fungus, were obtained from tetraploid and hexaploid wheat in the central highlands of Ethiopia, and a smaller number from Kenya, from 2011 to 2013, in order to determine the genetic diversity of this wheat pathogen in a center of host diversity. Single-uredinial isolates were derived and tested for virulence phenotype to 20 lines of Thatcher wheat that differ for single leaf rust resistance genes and for molecular genotypes with 10 simple sequence repeat (SSR) primers. Nine virulence phenotypes were described among the 193 isolates tested for virulence. Phenotype BBBQJ, found only in Ethiopia, was predominantly collected from tetraploid wheat. Phenotype EEEEE, also found only in Ethiopia, was exclusively collected from tetraploid wheat and was avirulent to the susceptible hexaploid wheat 'Thatcher'. Phenotypes MBDSS and MCDSS, found in both Ethiopia and Kenya, were predominantly collected from common wheat. Phenotypes CCMSS, CCPSS, and CBMSS were found in Ethiopia from common wheat at low frequency. Phenotypes TCBSS and TCBSQ were found on durum wheat and common wheat in Kenya. Four groups of distinct SSR genotypes were described among the 48 isolates genotyped. Isolates with phenotypes BBBQJ and EEEEE were in two distinct SSR groups, and isolates with phenotypes MBDSS and MCDSS were in a third group. Isolates with CCMSS, CCPSS, CBMSS, TCBSS, and TCBSQ phenotypes were in a fourth SSR genotype group. The diverse host environment of Ethiopia has selected and maintained a genetically divergent population of P. triticina.

Physiologic Specialization of Puccinia triticina on Wheat in the United States in 2014.

Collections of Puccinia triticina obtained from wheat fields and breeding plots in the Great Plains, Ohio River Valley, and southeastern states, were tested for virulence in 2014 in order to determine the virulence of the wheat leaf rust pathogen population in the United States. Single uredinial isolates (380 total) were derived from the collections and tested for virulence phenotype on 20 lines of Thatcher wheat that are near-isogenic for leaf rust resistance genes. In 2014, 55 virulence phenotypes were described in the United States. Virulence phenotypes MBTNB, TBBGS, and TCRKG were the three most common phenotypes. Phenotypes MBTNB and TCRKG are both virulent to Lr11, and TCRKG is also virulent to Lr18 and Lr26. MBTNB and TCRKG were most common in the soft red winter wheat region of the southeastern states and the Ohio Valley. Phenotype TBBGS is virulent to Lr39, which is present in the hard red winter wheat cultivars, and Lr21, which is present in the hard red spring wheat cultivars. Isolates with virulence to Lr11, Lr18, and Lr26 were most common in the southeastern states and Ohio Valley region. Isolates with virulence to Lr21 and Lr39 were most common in the hard red wheat region of the southern and northern Great Plains.

Collections of Puccinia triticina in Different Provinces of China Are Highly Related for Virulence and Molecular Genotype.

Collections of Puccinia triticina, the wheat leaf rust pathogen, were obtained from seven provinces in China from 2009 and 2010. Single uredinial isolates were derived and tested for virulence phenotype to 20 lines of Thatcher wheat that differ for single leaf rust resistance genes, and for molecular genotype with 23 simple sequence repeat (SSR) primers. Forty-eight virulence phenotypes were described among the 155 isolates tested for virulence. All but four isolates were virulent to Lr26, and no isolates with virulence to Lr18 or Lr24 were found. The three most common phenotypes, FCBQQ, PCGLN, and PCGLL, were found in five, five, and three provinces, respectively. Thirty-six SSR genotypes were found among the 100 isolates tested for molecular variation. Isolates with identical virulence phenotypes and SSR genotypes were found in more than one province. Analysis of variation showed no overall differentiation of SSR genotypes or virulence phenotypes based on province of origin. The SSR genotypes had high levels of linkage disequilibrium, high levels of observed heterozygosity, and significant correlation with the virulence phenotypes, all measures that indicated clonal reproduction. Bayesian cluster analysis and principle component plots indicated three groups of SSR genotypes that also varied significantly for virulence. The seven provinces are continuously adjacent to each other and likely form a single epidemiological zone for P. triticina.

Physiologic Specialization of Puccinia triticina on Wheat in the United States in 2013.

Collections of Puccinia triticina were obtained from rust-infected leaves provided by cooperators throughout the United States and from wheat fields and breeding plots by USDA-ARS personnel and cooperators in the Great Plains, Ohio River Valley, and southeastern states in order to determine the virulence of the wheat leaf rust population in 2013. Single uredinial isolates (490 total) were derived from the collections and tested for virulence phenotype on 20 lines of Thatcher wheat that are near-isogenic for leaf rust resistance genes. In 2013, 79 virulence phenotypes were described in the United States. Virulence phenotypes MBTNB, TNBGJ, and MCTNB were the three most common phenotypes. Phenotypes MBTNB and MCTNB are both virulent to Lr11, and MCTNB is virulent to Lr26. MBTNB and MCTNB were most common in the soft red winter wheat region of the southeastern states and Ohio Valley. Phenotype TNBGJ is virulent to Lr39/41 and was widely distributed throughout the hard red winter wheat region of the Great Plains. Isolates with virulence to Lr11, Lr18, and Lr26 were common in the southeastern states and Ohio Valley region. Isolates with virulence to Lr21, Lr24, and Lr39/41 were frequent in the hard red wheat region of the southern and northern Great Plains.

First Report of a Wheat Leaf Rust (Puccinia triticina) Phenotype with High Virulence to Durum Wheat in the Great Plains Region of the United States.

Phenotypes of the wheat leaf rust pathogen Puccinia triticina with high virulence to tetraploid durum wheat (Triticum turgidum) are found regularly in Mexico (5), the Mediterranean region (1), the Middle East (3), and rarely in the Imperial Valley of California and the adjacent area in Arizona. Previous to 2013, these phenotypes had not been found in the Great Plains region of the United States where hexaploid, T. aestivum types of hard red winter wheat, hard red spring wheat, and durum wheat are grown. In May 2013, collections of P. triticina, the wheat leaf rust fungus identified by color, size, and shape of uredinia, were obtained from leaves of the hard red winter wheat cultivar Overley in research plots at Hutchinson, KS. A single uredinial isolate was obtained that was used in virulence testing and molecular genotyping. Urediniospores from the initial field collection were inoculated onto seedlings of the susceptible cultivar Little Club. Subsequently, single uredinia were isolated and re-increased on Little Club. The single uredinial isolate was initially inoculated to 7-day-old seedlings of 20 lines of Thatcher wheat that are near-isogenic for leaf rust resistance genes and are used in the annual virulence surveys of P. triticina in the United States (2). The phenotype of the isolate, based on virulence to the 20 differential lines, was BBBQD (2), which was identical to phenotypes of P. triticina with high virulence to durum wheat from other regions where durum wheat is commonly grown (4). This phenotype had intermediate infection type of 2+ (moderate size uredinia with chlorosis) to the line with Lr2c and high infection types of 3+ (large uredinia with no chlorosis or necrosis) to lines with genes LrB, Lr10, and Lr39/41. Overley wheat has Lr39/41. The isolate was further tested on an additional set of 27 Thatcher lines, the cultivar Gatcher with Lr27 + Lr31, and a set of 15 durum wheat cultivars that have been grown in the United States and Canada. The isolate had virulence to lines with genes Lr14b, Lr20, Lr23, Lr33, Lr44, and Lr64. Notably, the isolate had distinct low infection types to seedlings of Thatcher lines with genes Lr12, Lr13, Lr22a, Lr35, and Lr37 that are usually optimally expressed in adult plants to most P. triticina isolates. The isolate had high virulence to all of the durum wheat cultivars. The single uredinial isolate of P. triticina from Overley was also genotyped with microsatellite alleles used in previous studies with P. triticina collections from durum wheat (3). The isolate from Kansas had a highly similar genotype to other isolates of P. triticina from worldwide durum-producing regions (3). This isolate with high virulence to durum wheat most likely migrated to the southern Great Plains region from the durum-growing regions in Mexico. Cultivars such as TAM 112, Armour, Winterhawk, and Bullet with Lr39/41 and other cultivars with Overley in their pedigree are currently grown throughout the southern Great Plains. Since many of the P. triticina phenotypes with high virulence to durum wheat are virulent to Lr39/41, these cultivars may provide a pathway for the spread of these phenotypes to the major durum-producing areas of North Dakota and Saskatchewan. References: (1) H. J. Goyeau et al. Plant Pathol. 61:761, 2012. (2) J. A. Kolmer and M. A. Hughes. Plant Dis. 97:1103, 2013. (3) M. E. Ordoñez and J. A. Kolmer. Phytopathology 97:574, 2007. (4) M. E. Ordoñez and J. A. Kolmer. Phytopathology 97:344, 2007. (5) R. P. Singh et al. Plant Dis. 88:703, 2004.

Physiologic Specialization of Puccinia triticina on Wheat in the United States in 2012.

Collections of Puccinia triticina were obtained from rust-infected leaves provided by cooperators throughout the United States and from wheat fields and breeding plots by United States Department of Agriculture-Agricultural Research Service personnel and cooperators in the Great Plains, Ohio River Valley, southeastern states, and Washington State and Idaho in order to determine the virulence of the wheat leaf rust population in 2012. Single uredinial isolates (501 in total) were derived from the collections and tested for virulence phenotype on 20 lines of 'Thatcher' wheat that are near-isogenic for leaf rust resistance genes. In 2012, 74 virulence phenotypes were described in the United States. Virulence phenotypes TNBGJ, TCRKG, and MBTNB were the three most common phenotypes. Phenotype TNBGJ is virulent to Lr39/41 and was widely distributed throughout the hard red winter wheat region of the Great Plains. Phenotype TCRKG is virulent to Lr11, Lr18, and Lr26 and was found mostly in the soft red winter wheat region in the eastern United States. Phenotype MBTNB is virulent to Lr11 and was also found mostly in the soft red winter wheat region. The frequency of isolates with virulence to Lr39/41, which is present in many hard red winter wheat cultivars in the Great Plains region, continued to increase. Isolates with virulence to Lr21, which is present in many hard red spring wheat cultivars, also continued to increase in frequency in the northern Great Plains region.

Physiologic Specialization of Puccinia triticina on Wheat in the United States in 2011.

Collections of Puccinia triticina were obtained from rust-infected leaves provided by cooperators throughout the United States and from wheat fields and breeding plots by USDA-ARS personnel and cooperators in the Great Plains, Ohio River Valley, southeastern states, Oregon, and Washington State in order to determine the virulence of the wheat leaf rust population in 2011. Single uredinial isolates (440 total) were derived from the collections and tested for virulence phenotype on 18 lines of Thatcher wheat and a winter wheat line that are near-isogenic for 19 leaf rust resistance genes. In 2011, 87 virulence phenotypes were described in the United States. Virulence phenotypes TBBGJ, MLDSD, and TCRKG were the three most common phenotypes. Phenotype TBBGJ is virulent to Lr39/41 and was widely distributed throughout the hard red winter wheat region of the Great Plains. Phenotype MLDSD is virulent to Lr17 and Lr39/41 and was widely distributed throughout the United States. Phenotype TCRKG is virulent to Lr11, Lr18, and Lr26 and was found mostly in the soft red winter wheat region in the eastern United States. Isolates with virulence to Lr39/41 and avirulence to Lr9 were prevalent in the Great Plains region for the first time. Virulence to Lr21 was present in five virulence phenotypes mostly from the spring wheat region of the northern Great Plains.

Physiologic Specialization of Puccinia triticina on Wheat in the United States in 2010.

Collections of Puccinia triticina were obtained from rust-infected leaves provided by cooperators throughout the United States and from wheat fields and breeding plots by United States Department of Agriculture-Agricultural Research Service personnel and cooperators in the Great Plains, Ohio River Valley, southeastern states, Oregon, and Washington State in order to determine the virulence of the wheat leaf rust population in 2010. Single uredinial isolates (537 total) were derived from the collections and tested for virulence phenotype on 19 lines of 'Thatcher' wheat and a winter wheat line that are near-isogenic for 20 leaf rust resistance genes. In 2010, 38 virulence phenotypes were described in the United States. Virulence phenotypes MLDSD, TDBJG, and TCRKG were the three most common phenotypes. Phenotype MLDSD is virulent to Lr17 and Lr39/Lr41 and was widely distributed throughout the United States. Phenotype TDBJG is virulent to Lr24 and was found in both the soft red winter wheat and hard red winter wheat regions. Phenotype TCRKG is virulent to Lr11, Lr18, and Lr26 and was found mostly in the soft red winter wheat region in the eastern United States. Virulence to Lr21 was found for the first time in North America in isolates collected from spring wheat cultivars in North Dakota and Minnesota.