Wheat landrace PI 177906 has seedling and field resistance to Pgt races TTKSK and TTKST. From a cross between PI 177906 and LMPG-6, 138 doubled haploid (DH) lines and 144 recombinant inbred lines (RILs) were developed and tested for seedling resistance to Pgt race TTKSK. Goodness-of-fit tests from both populations indicated that two dominant genes in PI 177906 conditioned resistance to race TTKSK. Parents and the 138 DH lines were evaluated in the field in two experiments in Kenya; one in the main season and one in the off-season. The 90K wheat iSelect SNP genotyping platform was used to genotype the parents and DH lines and data were used to construct a genetic linkage map. Two loci for seedling resistance were mapped to chromosomes 2BL and 4BL. Two major QTL for field resistance mapped to the same regions, a 14.4 cM interval on 2BL and an 8.5 cM interval on 4BL. The QTL on 2BL and 4BL explained, respectively, 31.9-32.3% and 18.2-19.1% of the variation in the off-season and 28.3-30.4% and 5.4-6.5% of the variation in the main-season. Based on the mapping results, race specificity, and the seedling infection types, the resistance gene in 2BL could be Sr28, whereas the gene on chromosome 4BL could be novel. The mapping results will be verified in the RIL population using the flanking SNP markers in KASP assays.
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The quest for durable rust resistance in wheat is burgeoning with the emergence of new virulent races. Breeders challenged with this unceasing plant-pathogen arms race have to devise strategies for effective evaluation and exploitation of the rust resistance genes. Considering the likely presence of useful variation for rust resistance in CIMMYT’s international bread wheat screening nurseries (IBWSN), we implemented genomic prediction in the 45th and 46th IBWSN entries to determine their genomic estimated breeding values (GEBV’s) for leaf, stem and stripe rust resistance. The 350 lines (45th IBWSN) and 329 lines (46th IBWSN) were phenotyped in replicated trials over two to three years in El Batan, Mexico (leaf rust); Njoro, Kenya (stem rust) and Toluca, Mexico (stripe rust). The filtered genotyping data for these two nurseries comprised of 6,786 and 11,218 genotyping by sequencing (GBS) markers. Our objective was to compare the GEBV’s estimated by four different models: multiple linear regression (MLR) with QTL-linked markers as fixed effects; Genomic-best linear unbiased prediction (G-BLUP); G-BLUP mixed model which includes QTL linked markers as fixed effects and Bayesian least absolute shrinkage and selection operator (LASSO). We observed that the prediction accuracies (calculated using 10-fold cross validation) were the highest for stripe rust (0.52 to 0.61), followed by stem rust (0.42 to 0.65) and leaf rust (0.15 to 0.45). Among the models, the MLR gave the lowest prediction accuracies (0.15,0.42 and 0.52), while G-BLUP (0.45,0.59 and 0.59), mixed G-BLUP (0.38,0.65 and 0.62) and the Bayesian LASSO (0.45,0.58 and 0.61) yielded relatively higher and almost similar accuracies. Overall, our results are promising and indicate that using genome-wide markers is advantageous than including only significant QTL-linked markers. We hope that implementing genomic prediction in breeding programs, would help to achieve rapid gains from selection and revolutionize our efforts in combating the rust pathogen.
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.
Stem rust is a major threat to wheat production in Georgia. Breeding for resistance to the rusts is a major strategy for wheat improvement programs. Our objective was determination of the stem rust resistance levels in entries of the 4nd International Winter Wheat Stem Rust Resistance Nursery. Responses of 85 varieties/lines were evaluated in an inoculated field nursery. A coefficient of infection (CI) and area under the disease progress curve (AUDPC) were estimated for each entry. Fifteen entries (T03/17, TAM-107/T21, SD92107-2/SD99W042, KS95U522/TX95VA0011/F1/JAGGER, AR800-1-3-1/NW97S320, FL9547/NC00-14622, FL9547/TX00D1626, TAM302/KS93U450, MCCORMİCK/TREGO, NC00-14622/2137, TAM200/KAUZ//GOLDMARK/3/BETTY, KS920709-B-5-1-1/BURBOT-4, AFINA SOMNEZ, TAM200/KAUZ/4/BEZ/NAD//KZM(ES85.24/3/F900K) were resistant; 39 showed moderate resistance; 15 were scored MR-MS and 17 were moderately susceptible. Most of entries had very low CI (0.2 - 0.5) and AUPDC (less than 10.0); the best including T07/08, T07/09, T08/02, T08/01, T08/02, T08/04, CAKET/PEHLIVAN, ID800994.W/VEE//PIOPIO/3/MNCH/4/FDL4/KAUZ, PBI1013.13.3/3233.35 /3/STAR//KAUZ/STAR, DULGER-1//VORONA/BAU, ZANDER-17/3/YE2453/KA//1D13.1/MLT, 55-1744/7C//SU/RDL/3/CROW/4/MILAN/5/ITOR, 1D13.1/MLT//TUI/3/S?NMEZ/4/ATAY/GALVEZ87, TAM107//ATAY/GALVEZ87, HBF0290/X84W063-9-39-2//ARH/3/LE2301, STAR/BWD/3/PRL/VEE#6//CLMS, FRTL//AGRI/NAC/3/KALYOZ-17, CV. RODİNA/AE.SPELTOİDES10 KR, TAM 107//ATAY/ GALVEZ87, and 06393GP1. The severities for susceptible entries varied from 20 to 70%, with checks Morocco and Bezostaya 1 at 80% and 60%, respectively. However, the majority of entries (94%) had average CI of 0.2 - 20 and five entries with CI 21 - 40 had high to moderate levels of resistance.
Wheat is one of the three most important food crops of Nepal for which rusts (Puccinia triticina, P.striiformis and P.graminis) are major biotic stresses. Leaf rust is widespread and causes 14-20% yield losses and speculated that P.triticina over summer on self-sown wheat in hills of Nepal. Twenty two different pathotypes of P.triticina have been recorded while thirteen leaf rust resistant genes (Lr1, Lr3, Lr10, Lr13, Lr14a, Lr16, Lr17, Lr19, Lr23, Lr26, Lr27, Lr31 and Lr34) either singly or in combinations, impart resistance to wheat genotypes in Nepal. Yellow rust is also a major disease in mid and lower hills, river basin and valleys, causing 30-80 % grain yield losses. Twenty-nine pathotypes of P.striiformis have been recorded till now in Nepal while nine Yr genes (Yr2, Yr2 KSA, YrA, Yr6, Yr7, Yr9, Yr27, GA, and SU) have been postulated. Stem rust is a minor and sporadic disease in central, western, mid-western region late in the season. Nine Sr genes (Sr2, Sr5, Sr7b, Sr8, Sr8a, Sr9b, Sr11, Sr25 and Sr31) have been characterized. Vijay was the first Ug99 resistant wheat variety released for cultivation. Previous experiences show that Nepal served as a focal point of wheat rusts for further spread in the Gangetic plains of India due to presence of more than 25 species of Berberis in hills of Nepal. Efforts are underway to survey rusts infection on Berberis spp. Use of Tilt (Propiconazole), Triadimefon (Bayleton) and Indar (RH-124) was found effective to reduce leaf rust as well as foliar blight. Cultivation of resistant varieties in Nepal not only reduces rust severity in this country but also minimizes crop losses in other neighboring countries especially India. This demands the need for regional collaboration in South Asia to combat wheat rusts.
Resistance is the most economically viable approach to curb the threat of rusts in wheat. The defeat of Sr31 and vulnerability of other resistance genes to the highly virulent Pgt race Ug99 and variants led to renewed efforts to discover and deploy resistance genes/QTLs in new durably resistant varieties. Akuri is a CIMMYT-developed bread wheat line exhibiting adult plant resistance (APR) in field trials in Kenya despite susceptibility to many races at the seedling stage. This study was designed to identify genomic regions contributing APR to stem rust in Akuri. One hundred and forty one RILs and parents of an F2:5 Akuri x PBW343 population were evaluated in Njoro for APR to stem rust over three seasons. Composite interval mapping was implemented on Windows QTL Cartographer to detect QTLs at a LOD threshold of 2.5 utilizing 910 high quality SNPs previously typed on the DArT-GBS platform. Preliminary QTL analyses revealed loci on chromosomes 1B, 2B and 3B consistently contributing to stem rust resistance. These QTL respectively explained ~7, 9, and 8% of the phenotypic variation. A comparison with the recently reported QTL consensus map revealed that the QTL herein discovered are probably novel. Work is underway to saturate the identified genomic regions with microsatellite markers to identify candidate, linked markers for use in marker assisted selection (MAS)
Stem rust is a globally important wheat disease that can cause severe yield loss. Breeding for quantitative stem rust resistance (QSRR) is important for developing cultivars with durable resistance. Genomic selection (GS) could increase rates of genetic gain for quantitative traits, but few experiments comparing GS and phenotypic selection (PS) have been conducted. Our objectives were to compare realized gain from GS based on markers only with that of PS for QSRR in spring wheat using equal selection intensities; determine if gains agree with theoretical expectations; and compare the impact of GS and PS on inbreeding, genetic variance, and correlated response for pseudo-black chaff (PBC), a correlated and likely pleiotropic trait. Over two years, two cycles of GS were performed in parallel with one cycle of PS, with each method replicated twice. For GS, markers were generated using genotyping-by-sequencing, the prediction model was initially trained using historical data, and the model was updated before the second GS cycle. Overall, GS and PS led to a 31±11 and 42±12% increase in QSRR and a 138±22 and 180±70% increase in PBC, respectively. Genetic gains were not significantly different, but were in agreement with expectations. Per year, gains from GS and PS were equal, but GS led to significantly lower genetic variance. This shows that while GS and PS can lead to equal rates of short-term gains, GS can reduce genetic variance more rapidly. Further work to develop efficient GS implementation strategies in spring wheat is warranted.
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.
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.
The objective of this study was to characterize seedling and adult plant resistance to all three rusts in a set of 40 bread wheat varieties currently cultivated in Tajikistan. Gene postulation based on multi-pathotype seedling test data and adult plant responses identified Yr2, Yr9, Yr17 and Yr27; Lr10 and Lr26; and Sr5, Sr6, Sr10, Sr11, Sr31 and Sr38. The effects of slow rusting, adult plant, pleiotropic resistance genes Lr34/Yr18/Sr57 and Yr30/Lr27/Sr2 were observed in the field and confirmed with molecular markers. Furthermore, molecular markers diagnostic for Yr9/Lr26/Sr31 and Yr17/Lr37/Sr38 were assessed on all varieties. Genes Lr34/Yr18/Sr57, Yr9/Lr26/Sr31 and Yr27 were identified in varieties Sarvar, Vahdat, Oriyon, Isfara, Ormon, Alex, Sadokat, Ziroat-70, Iqbol, Shokiri, and Safedaki Ishkoshimi based on phenotypic and genotypic results. Some lines were highly resistant to stripe rust (4 varieties), leaf rust (5) and stem rust (9), but the genes responsible could not be identified. They may possess new resistance genes. We thus identified combinations of major and minor rust resistance genes in Tajik wheat varieties. These varieties can now be used by breeders in Tajikistan as crossing parents to develop new varieties with durable resistance to the rusts.