Stem and leaf rusts affect the winter and spring wheat in the Novosibirsk region. During 2008-2017 leaf rust incidence was generally moderate, from 20 to 40%. A leaf rust outbreak occurred in 2015 when incidence increased up to 80%. Leaf rust severity on the 'Thatcher' NILs ranged from immune or resistant to highly susceptible host response with maximum severity of 90S. Lines carrying genes Lr17, Lr18, Lr24, Lr29, Lr35, Lr37, Lr44, and LrW remained almost free of infection for the whole time of inspection. Genes Lr12, Lr13, Lr28, Lr34, and Lr38 exhibited moderate resistance but they did not provide sufficient level of resistance in favorable conditions. Since race-specific genes Lr24 and Lr29 are still effective in the neighboring Novosibirsk and Omsk regions, they might be recommended for breeding purposes in Western Siberia.
In 2016 stem rust was more prevalent and widespread in the region than ever before. Disease incidence ranged between 4.5 - 60% with high severity up to 80S in six fields from seven observed locations. The 4th ISRTN and varieties carrying Sr31 of West Siberian germplasm were assessed in field trials to monitor the virulence of the local population. There was no virulence to Sr9b, Sr9e, Sr20, Sr28, Sr29, Sr33, Sr39, Sr40, SrWld, Sr2 complex. Possible virulence to Sr6, Sr11, Sr12, Sr13, Sr17, Sr24, Sr25, Sr30, Sr31, Sr35, Sr38, Sr44, Sr57 was observed with low frequency. Entries genotyped for gene Sr31 were scored as MS and S. However, follow up race analysis work is needed to determine the actual stem rust races present and confirm the suspected possible observed virulence on Sr31.
Primary Author: Skolotneva, The Federal Research Center Institute of Cytology and Genetics, The Siberian Branch of the Russian Academy of Sciences
Variants of Puccinia triticina race BBG/BN, separately overcoming three resistance genes, were identified from durum wheat (Triticum turgidum ssp. durum) fields in northwestern Mexico since its introduction in 2001. Major genes available for use in breeding programs are limited and an alternative strategy is required. Previous studies indicated that slow rusting resistance in eight CIMMYT durums was determined by 2 to 3 minor genes with additive effects. Twenty-eight 4-way crosses were made between these lines with the aim of developing new germplasm with enhanced levels of resistance through pyramiding diverse minor genes. Plants in F1 (4-way) through F3 generations were selected for slow rusting under high leaf rust pressure at the Cd. Obregon and El Batan field sites in Mexico and spikes from selected plants were harvested as bulks. Plants in the F4 generation were individually harvested and1,843 advanced lines obtained, among which 106 lines with enhanced resistance, and desirable agronomic and grain characteristics were selected for non-replicated yield and leaf rust evaluation trials at Obregon during the 2007-2008 season. The best 19 lines, exhibiting near-immunity but with the presence of a few susceptible type pustules, parents and susceptible checks were evaluated for leaf rust resistance under very high disease pressure in replicated trials sown on two dates (16 May and 6 June) at El Batan during 2008. Spreader rows of susceptible cultivar ‘Banamichi C2004’, sown as border and as hills on one side of each plot, were inoculated with P. triticina race BBG/BP. Leaf rust severities, and host responses to infection were determined from weekly readings, and area under the disease progress curves (AUDPC) were calculated. Several lines were identified with significantly lower final leaf rust severity responses and AUDPC values than the most resistant parent in each cross. Our results show that enhanced levels of slow rusting can be generated by pyramiding diverse genes present in different parents. The trial is being repeated during the 2008-2009 season at Obregon to validate the results. In addition these lines are being used for transferring slow rusting resistance into high yielding, superior quality adapted backgrounds using the single-backcross approach.
Primary Author: Slyvia Herrera-Foessel, CIMMYT
Genomic selection facilitates rapid cycling through a breeding cycle by eliminating the need to phenotype prior to selecting superior parents and crossing among them. In winter wheat we can now complete a cycle of GS in about 12 months and two greenhouse seasons. Season consists of planting F1s from the previous cycle and selfing to obtain F2 seed. The second season involves planting and genotyping the F2s, predicting their value with GS, selecting and crossing the best, and harvesting the F1 seed. Our breeding program has completed five cycles of GS in one population primarily for grain yield, over the past five years. We have completed three cycles of GS for resistance to Fusarium Head Blight in a second population. Genotyping was done using genotyping-by-sequencing. This provides an opportunity to assess the changes in the population that have occurred as a result of this rapid cycling. These include 1) changes in genomic estimated breeding values for grain yield and FHB resistance, 2) effect of selection and drift on allele frequencies including fixation, 3) effect of selection on diversity and genetic relationships, and 4) changes in linkage disequilibrium. We are conducting these analyses and will present the results.
Primary Author: Sneller, The Ohio State University
The new arrival of wheat rust pathotypes through migration during wheat cropping season requires regular monitoring to secure wheat production. In the present study, we collected leaf rust (Puccinia triticina Eriks.) infected wheat leaves from three major wheat growing provinces of Pakistan in the year 2014 to assess the haplotype diversity of P. triticina (Pt) isolates. The rDNA ITS sequence data of collected isolates was used in NCBI BLAST analysis. The blast hits showed best matches with Pt accessions EU014050 (Iran), JN120331 (Iran), JX533577 (Iran), AY956549 (Iran), DQ417412 (Czech Republic), DQ417418 (Israel), DQ417413 (Slovakia) and AF511083 (Louisiana). However, in cluster analysis, the Pakistani isolates showed strong bootstrap support with only Iranian and Indian (races 77-5 & 104-4) accessions that indicated eastward migratory mode of Pt pathotypes in Pakistan through westerly wind patterns. The predominant genotype DQ417412 (similar in alignment with AY956549 from Iran) overcome the resistance of top Pakistan mega varieties Seher06, Inqilab91, Kiran95, SKD1, TJ83 and NIFA-Batoor. Hence, the ITS based information remains a rapid molecular tool for pathogen surveillance across countries and continents.
Primary Author: Sohail, Department of Botany, Faculty of Biology, Government College Murree, Pakistan
Four Ug99 pathotypes occur in southern Africa. Although South African bread wheat cultivars and lines are regularly screened against representative isolates, the stem rust reactions of Zimbabwean germplasm to these variants were largely unknown. A collection of 49 wheat cultivars and lines, obtained from Seed-Co (Ltd.) and the Crop Breeding Institute in Zimbabwe, were tested as seedlings against pathotypes TTKSF, TTKSF+, TTKSP and PTKST. Twelve varieties and 21 experimental lines showed low infection types with all four pathotypes. Using molecular marker assays Sr31 was detected in 26 entries, Sr24 in five and Sr36 in one. The csSr2 marker suggested the presence of Sr2 in 20 entries. Screening of adult plants in the greenhouse using pathotype PTKST showed 34 entries with low infection types and 15 had high infection types. Stem rust field records in 2012 showed 5 susceptible entries with stem rust scores between 50S and 80S, whereas only 4 susceptible entries were identified in 2014 with scores ranging from 30S to 80S. Three lines were susceptible in both seasons. The study exposed the vulnerability of Zimbabwean wheat germplasm to Ug99 variants, but also identified suitable lines that can be used in breeding and possible commercialization.
Primary Author: Soko, Seed-Co Ltd., Rattray Arnold Research Station, Zimbabwe
Notwithstanding the re-emergence and importance of wheat stem rust caused by Puccinia graminis f. sp. tritici (Pgt), the degree of protection provided by different types of resistance has not been carefully investigated in contemporary studies. Seven wheat entries were exposed to stem rust infection and fungicide response in a split-plot field experiment over two seasons. Severe epidemics of Pgt race PTKST, generated by frequent inoculation of spreader rows within and around the trial, developed in both years. By comparing grain yield in rusted and fungicide sprayed plots, varieties SC Nduna (Sr31) and SC Stallion (Sr2+Sr31) sustained mean yield losses of 28.8% and 20.7%, respectively. From entries with adult plant resistance (APR), Kingbird recorded a loss of 10.1% as compared to W1406 (19.5%) and W6979 (15.4%). Grain yield of SC Sky which exhibits all stage resistance (ASR) was reduced by 6.4% over the two seasons. The highest yield loss (47.9%) was measured for Line 37, the susceptible control. A significant linear relationship occurred between percentage yield loss and AUDPC in both seasons (R2=0.99 and 0.83). This study showed that not all sources of APR to stem rust provided the same level of protection under severe disease pressure. In the absence of virulence for SC Sky, ASR conferred the most protection.
Primary Author: Soko, University of the Free State and Seed-Co
Durable resistance to wheat stem rust fungus can Be achieved by developing and deploying varieties that have race-nonspecific, adult plant resistance (APR) conferred by multiple minor, slow rusting genes. Wheat lines ‘Kingbird, ‘Kiritati’, ‘Huirivis#1’, ‘Juchi’, ‘Muu’ and ‘Pavon 76’ showed high levels of APR to Ug99 races of stem rust fungus when tested in Kenya. The F5 and F6 generation recombinant inbred line (RIL) populations developed from the crosses of moderately susceptible ‘PBW343’ with five resistant parents were used in mapping. The non-Sr26 fraction of the ‘Avocet’ x Pavon 76 RIL population, developed earlier for leaf rust and stripe rust resistance studies, was also included. Field phenotyping of the parents and RILs were conducted at Njoro, Kenya for at least two years with Ug99+Sr24 (TTKST) race under high stem rust pressures. The continuous variation of APR in each RIL population and genetic analyses indicated quantitative nature of resistance that was likely governed by 3 or 4 minor genes. Single and joint year analyses by Inclusive Composite Interval Mapping (ICIM) using informative DArT and/or SSR markers identified consistent APR QTLs on chromosomes 1AL, 3BS, 5BL, 7A and 7DS in Kingbird; 2D, 3BS, 5BL and 7DS in Kiritati; 2B, 3BS, 4A, 5BL and 6B in Juchi; 2B, 3BS, 7B in Huirivis#1; 2B, 3BS and 5BL in Muu; and 1BL, 3BS, 5A and 6B in Pavon 76. QTLs on each genomic regions explained 10- 46% of the phenotypic variation for APR. Pseudo-black chaff phenotype associated with APR gene Sr2 on chromosome 3BS in all six resistant parents and identification of an APR QTL in the same region in all mapping populations confirmed the role of Sr2 in reducing stem rust severity. The 1BL QTL in Pavon 76 was in the same region where pleiotropic APR gene Lr46/Yr29/Pm39 is located. Similarly a 7DS QTL in Kingbird and Huirivis#1 was in the chromosomal region where pleiotropic APR gene Lr34/Yr18/Pm38 is located. These results indicate that the above two pleiotropic resistance genes confer APR to stem rust in addition to leaf rust, yellow rust and powdery mildew. Further studies are underway to saturate the genomic regions harboring new APR QTLs with additional molecular markers.
Primary Author: Sridhar Bhavani, CIMMYT-Kenya
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.
Primary Author: Steffenson, 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.
Primary Author: Steffenson, Department of Plant Pathology, University of Minnesota, USA
In the Triticum genus, tetraploid T. turgidum is a useful resource for germplasm improvement of hexaploid common wheat (T. aestivum). Several recent studies demonstrated that Pgt race TTKSK resistant genotypes were abundantly present among seven tetraploid subspecies (T. turgidum subsp. carthlicum , dicoccum , dicoccoides , durum, polonicum , turgidum , and turanicum ). In an effort to improve common wheat for TTKSK resistance, we have been transferring stem rust resistance from tetraploid to hexaploid wheat through production of synthetic hexaploid wheat (SHW) or direct hexaploid × tetraploid hybridization followed by backcrossing. For production of SHW lines, we selected 181 unique tetraploid genotypes from the seven tetraploid subspecies for crosses with 14 accessions of Aegilops tauschii (2 n = 2 x = 14, DD) and developed 200 new SHW lines from these crosses. We are currently characterizing these lines for reaction to stem rust. So far, 80 SHW lines and their parents have been evaluated for reaction to races TTKSK, TRTTF, TTTTF and six other U.S. races and genotyped using molecular markers linked to known resistance genes previously identified in T. turgidum subsp. dicoccum and Ae. tauschii. The evaluation data showed that 42, 40, and 52 SHW were resistant to races TTKSK, TRTTF, and TTTTF respectively, with 21 lines being resistant to all three races. Based on marker analysis and race specificity, we postulated that a number of SHW lines have novel genes conferring resistance to TTKSK and other races. For gene introgression through direct hybridization, we have transferred Sr47, which was recently transferred from Ae. speltoides into durum through marker-assisted chromosome engineering, from durum into adapted hard red spring wheat germplasm. The new SHW lines and adapted germplasm carrying unique stem rust resistance genes from the tetraploids represent new sources of stem rust resistance for hexaploid wheat improvement.
Primary Author: Steven Xu, USDA-ARS, Cereal Crops Research Unit, Fargo, ND, USA