Aegilops species are rich sources of resistance to Pgt race TTKSK
Department of Plant Pathology, University of Minnesota, USA
Wild relatives are rich sources of genetic diversity for wheat improvement. Our research focuses on characterizing stem rust resistance in Aegilops, a genus whose 23 species are part of the secondary genepool of wheat. In a previous study, we evaluated nine Aegilops species (885 total accessions) from Israel for reaction to Pgt race TTKSK and found the frequency of resistance ranged from 14% for Ae. searsii to 100% for Ae. speltoides. To extend this investigation, we evaluated 231 additional Aegilops accessions from five of the same species, plus 165 accessions from seven uncharacterized species. All of these accessions were collected from countries other than Israel or were of unknown provenance. The frequencies of resistant accessions in Ae. speltoides (94% in this study vs. 100% previously), Ae. bicornis (93% vs. 79%), Ae. geniculata (48% vs. 45%), Ae. peregrina (50% vs. 57%), and Ae. searsii (10% vs. 14%) were very similar to those for the Israel cohort in the previous study with the exception of Ae. bicornis. Of the latter accessions, the highest frequencies of resistance were in Ae. cylindrica (88%) and Ae. columnaris (85%) followed by Ae. binuncialis (37%) and Ae. ventricosa (13%). Accessions resistant to race TTKSK were not found in Ae. crassa, Ae. juvenalis, or Ae. vavilovii. These data show that certain Aegilops species are particularly rich sources of resistance to TTKSK. Yet other species carry no resistance. Research is underway to characterize the genetics of resistance in several select accessions.
Identifying quantitative trait loci for high-temperature adult-plant resistance to stripe rust in six mapping populations of wheat
University of Idaho, USA
High-temperature adult-plant (HTAP) resistance to stripe rust in wheat has proven to be durable. Molecular markers tightly linked to HTAP resistance offer an alternative to phenotypic selection and are useful for pyramiding HTAP resistance genes with other types of resistance. This study assessed HTAP resistance in six diverse mapping populations derived from four types of crosses: 1. Resistant × Susceptible, IDO444 × Rio Blanco (winter wheat RILs) and UI Silver × Shaan 89150 (winter wheat DH lines); 2. Moderately Resistant × Resistant, UI Platinum × SY Capstone (spring wheat DH lines) and UI Stone × IDO686 (spring wheat RILs); 3. Moderately Resistant × Moderately Resistant, UI Stone × Alturas (spring wheat RILs); and 4. Moderately Susceptible × Moderately Susceptible, IDO835 × Moreland (winter wheat, DHLs). Eight QTL significantly associated with HTAP resistance were earlier identified in the IDO444 x Rio Blanco RIL population, including three major QTL (QYrid.ui-2B.1, QYrid.ui-2B.2, and QYrid.ui-4A) and five minor QTL (QYrid.ui-1A, QYrid.ui-3B.1, QYrid.ui-3B.2, QYrid.ui-4B, and QYrid.ui-5B) (Chen et al. 2012, Mol Breeding 29:791–800). These QTL are being validated and novel QTL are being identified in the other five populations. The current study used elite × elite crosses; therefore, the identified QTL may have application in selecting lines with combinations of stripe rust resistance and other superior agronomic traits and perhaps for release as new cultivars.
Sources of resistance to stem rust in the USDA Barley iCore Collection
Department of Plant Pathology, University of Minnesota, USA
Stem rust is an important disease of wheat and barley. Barley is genetically vulnerable to stem rust with few identified resistance genes and sources. Stem rust resistance breeding is largely based on the gene Rpg1, first incorporated into North American barley cultivars in the 1940s. To identify potentially new resistance sources, the USDA-ARS National Small Grains Barley iCore Collection (1,860 accessions) was evaluated for reaction to stem rust at the seedling and adult stages. The adult stage evaluations were conducted at Njoro, Kenya (race TTKSK/TTKST), and St. Paul, Minnesota (race QCCJB), for two seasons, and the seedling tests (race TTKSK) in the BSL-3 greenhouse at St. Paul, Minnesota. At St. Paul, between 7 and 10% (132-203) of the accessions exhibited resistance, whereas in Kenya, 11-14% (218-261) were resistant. Correlation between years was higher in Kenya (0.60) than it was at St. Paul (0.48). Approximately 15% (277) of the collection gave moderately low to low reactions to TTKSK at the seedling stage. From these initial tests, 290 accessions were chosen based on diversity of reaction, origin of plant material, or stability across environments. These accessions were then further evaluated with a suite of races at the seedling stage to postulate resistance genes. Of these selections, 244 gave reactions suggesting they carry adult plant resistance. The remaining 46 accessions gave low to very low reactions to one or more races. Based on country of origin and resistance spectrum 15 accessions were predicted to have the rpg4/Rpg5 complex, including a subset from Switzerland. The remaining 31 have a reaction spectrum, country of origin or pedigree that does not suggest the presence of the rpg4/Rpg5 complex. Molecular tests will be used to confirm the presence of this complex in these materials.
Breeding Studies of Resistant Varieties to Stripe and Stem Rust Diseases in West Transitional Zone of Turkey
Transitional Zone Agricultural Research Institute, Turkey
The most serious wheat diseases affecting yield and quality in West Transitonal Zone of Turkey is rust diseases. Breeding resistant varieties is the most economic and confident way to struggle with these diseases. In this study, it was aimed to determine the genotypes which are resistant to stripe and stem rust diseases existing in our region and use these genotypes as material in breeding program. The study was carried out in 2014 at natural and artificial epidemic conditions in the experimental field of Transitional Zone Agricultural Research Institute. The reactions of some wheat genotypes to stripe and stem rust diseases caused by the fungal agents P.striformis ve P.graminis were detected. For this purpose, 310 lines and 18 variety of bread wheat belonging to Transitional Zone Agricultural Researh Institute were sown in a way 1 m x 1 row. The disease assessments were conducted in May-June 2014 according to the Modified Coob Scale. As a result of infection coefficient observations, it was determined that 49% of the material are resistant to stripe rust and 60% of the material are resistant to stem rust.
The University of Minnesota Stakman-Borlaug Center (SBC) for Sustainable Plant Health: Ongoing support for rust research and education
Department of Plant Pathology, University of Minnesota, USA
The Stakman-Borlaug Center (SBC) for Sustainable Plant Health at the University of Minnesota builds upon the vision and contributions of the preeminent crop scientists E.C. Stakman and Norman Borlaug. Recognizing that the toughest problems in agriculture today require highly diverse approaches, the SBC leverages multidisciplinary expertise to address plant health issues that impact food security and ecosystem health through research and education. The focus of SBC activities is local, national, and international; the impact of the SBC is global. The SBC maintains and manages a diverse plant health research portfolio and leads multidisciplinary research initiatives, student training programs, and capacity building efforts. Current rust research-related activities include organizing and fostering the international oat rust community to investigate diseases such as crown rust and stem rust. By advocating for oat rust research funding at the institutional, national, and international levels and leveraging expertise in genomics, phenomics and informatics, the SBC aims to identify novel forms of rust resistance in wild oat relatives and non-hosts. The SBC also plays supporting and project management roles in other cereal rust research and capacity building efforts led by scientists at the University of Minnesota and USDA-ARS Cereal Disease Laboratory, including a project aimed at characterizing Pgt isolates with unique virulences from Ethiopia and a 6-week summer training program for rust researchers. The complete SBC research, education, and capacity building portfolio can be found at sbc.umn.edu.
Pseudo black chaff as evidence for recombination of Sr2 and Fhb1
SeCan Association, Canada
Resistances conferred by Sr2 and Fhb1 are considered important in the control of stem rust and Fusarium head blight (FHB), respectively, but these genes on chromosome 3BS are known only to occur in repulsion. The objective of this study was to use a doubled haploid (DH) population of Carberry/AC Cadillac to seek a recombinant with the Sr2 and Fhb1 resistance alleles in coupling. Carberry expresses moderate resistance to FHB. AC Cadillac has marker alleles typically linked to the Sr2 resistance allele. Carberry has marker alleles associated with Fhb1. The DH population was genotyped with 578 DArT®, 55 SSR, 2 BAC-derived, 2 CAPS, and 1 STS markers. The parents and 261 DH lines were evaluated for adult plant stem rust response (Ug99) at Njoro, Kenya, and at Swift Current, Canada (Canadian Pgt races). Response to FHB was evaluated in nurseries near Portage la Prairie, Manitoba. Pseudo black chaff (PBC), known to be tightly linked to Sr2, was scored in nurseries when symptoms were expressed. Both cultivars have other Sr and Fhb resistance genes, and QTLs contributing to PBC on chromosomes other than 3BS. Using phenotypic and molecular marker data, and the very tight linkage or pleiotropic relationship of Sr2 with PBC, DHs were classified for presence of PBC and FHB response. Putative recombinant DH candidates were re-evaluated for symptoms of PBC, stem rust, and FHB in three international nurseries and genotyped with markers closest to Sr2 and Fhb1. The results will be presented.
Genetic relationship between wheat stem rust resistance genes Sr36 and Sr39
The University of Sydney, Plant Breeding Institute, Australia
Stem rust resistance genes Sr39 (RL6082) and Sr36 (Cook) were transferred from Aegilops speltoides and Triticum timopheevi to chromosome 2B of wheat. Both genes are located on large translocated segments. Genotypes carrying Sr36 and Sr39 produce infection types (ITs) 0; and 2, respectively, against avirulent pathotypes. This investigation was planned to study the genetic relationship between these genes with the aim of combining them in a single genotype. Seedling tests on RL6082/Cook F3 lines showed complete repulsion linkage [25 Sr39Sr39sr36sr36 (IT2-) : 53 Sr39sr39Sr36sr36 (IT2-, IT0;) : 13 sr39sr39Sr36Sr36 (IT 0;)], and preferential transmission of the Ae. speltoides segment over the T. timopheevi segment was evident from the segregation ratio. The Sr39-carrying translocation was shortened by Niu et al. (2011; Genetics 187: 1011-1021) and the genetic stock carrying the shortest segment was named RWG1. Based on the reported location of Sr39 in the smaller alien segment in RWG1, we predicted that it should recombine with Sr36. F3 lines derived RWG1/Cook were phenotyped for stem rust response at the two-leaf stage and again complete repulsion linkage between Sr39 and Sr36 was observed [23 Sr39Sr39sr36sr36 (IT2-) : 78 Sr39sr39Sr36sr36 (IT0;, IT2-) : 68 sr39sr39Sr36Sr36 (IT 0;)]. In contrast to the cross involving the large Sr39 translocation, preferential transmission of the T. timopheevi segment was observed. These results indicated that a genetic determinant of meiotic drive had been deleted in the shortened Ae. speltoides segment. Genotyping with the co-dominant STS marker rwgs28 matched the phenotypic classification of F3 families. Marker rwgs28 was diagnostic for the Ae. speltoides segment, but the rwgs28 allele amplified in Cook was not T. timopheevi-specific.