In 2016 rust surveys were carried out in all the four key wheat growing regions: South Rift (June, July), Mount Kenya (July), North Rift (September) and Central Rift (part of August and September). A total of 304 farms were sampled. Stem rust was detected in 235 (78.3%), yellow rust in twenty-eight (9.3%) and leaf rust in fourteen (4.7%) of the farms. Stem and yellow rust were detected in all the wheat growing regions while leaf rust was detected in South, North and Central Rift. Stem rust infection ranged from TR to 90S with maximum infection in Central Rift (88.3%), Mt. Kenya region (80.3%); South Rift (76.5%) and North Rift (72.4%). Yellow rust infection ranged TR to 60S with maximum infection in Central Rift (16.7%); North Rift(13.3 %) and minimum infection in South Rift( 4.9%),) and Mt. Kenya region ( 1.7%). Leaf rust infection ranged from trace to 50S with maximum infection in North Rift (10.2%) minimum infection in Central Rift (3.3 %) and South Rift (1.2%). Fifty percent of the eight previously released wheat varieties are now susceptible to the Ug99 race. Race analysis results from AAFC Canada suggested the presence of TTKSK which was dominating in North Rift and TTKSK, TTKST and TTTTF were dominant in the screening nursery at Njoro. Yellow rust in the region has increased in the current year owing to the incursion of a probable new race AF2012 which has resulted in increased disease severity on varieties and materials tested in the International nurseries at KALRO, Njoro.
Primary Author: Wanyera, Kenya Agricultural and Livestock Research Organization
Keywords: stem rust, ug99
Genomic selection (GS) in wheat can accelerate yield gain principally through a reduction in breeding cycle duration. A method for rapid generation advance called ?speed breeding? (SB) enables up to six generations of spring wheat per year, and could be used to accelerate breeding population development and be combined with GS in various breeding schemes to enable even further gains. SB and GS could be combined through a variety of different scenarios using single seed descent and also by applying GS to segregating populations in the glasshouse. Selected lines could then go into multi-location field trials for final selections and to obtain information for updating the prediction model. The increase in speed in these scenarios compared with field-based breeding schemes could greatly improve genetic gain for valuable target traits, such as yield. To test these hypotheses, a 260 multi-parent spring wheat population, genotyped with 8,000 DArT polymorphic markers, underwent yield trials over three years. Yield prediction accuracy was accessed using five-fold cross validation and predicting across years. Using these results, the rate of genetic gain achieved through either phenotypic selection in the field or a combination of SB and GS in the glasshouse were calculated. Results indicate that incorporating GS into SB growing systems would result in a higher rate of genetic gain compared to phenotypic or more traditional GS breeding schemes, due to the greater number of generations produced per year. This approach may be able to be coupled with multi-trait GS prediction models to increase accuracy, advance genetic gain and wheat variety development.
Primary Author: Watson, University of Queensland
Keywords:
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)
Primary Author: Waweru, Department of Plant Breeding and Biotechnology, University of Eldoret, Kenya
Keywords: QTL, APR, stem rust, bread wheat, markers
Improvement of stripe rust resistance is one of the main aims of wheat breeding programs worldwide. Progress is dependent on the availability of genetically diverse and widely effective sources of resistance. This study focuses on genetic analysis of stripe rust resistance in landrace accession AWCC275 from the Watkins Collection. AWCC275 was scored resistant to moderately resistant under field conditions during three crop seasons and showed an intermediate seedling response (infection type 2C). AWCC275 was crossed with the susceptible genotype Avocet S and a population of 76 F3 families was generated. Twenty seedlings of each family were tested at the seedling stage with Puccinia striiformis f. sp. tritici pathotype 134 E16A+,Yr17+,Yr27+ under greenhouse conditions. Sixteen lines were homozygous resistant (HR), 43 segregated and 17 were homozygous susceptible (HS). Chi-squared analysis (?21:2:1 =1.34, non-significant at P=0.05 and 2 df) indicated segregation at a single locus. HR and HS lines were submitted for selective genotyping using the 90K SNP platform. The population is currently being advanced to F6 for detailed molecular mapping and the resistance gene is being backcrossed to three Australian wheat cultivars.
Primary Author: Wells, The University of Sydney Plant Breeding Institute Cobbitty, Faculty of Agriculture and Environment, Australia
Keywords: stripe rust, landrace, genetics
During the 2014/15 main crop season 831 wheat fields and experimental plots were assessed for diseases; 66.2% were in the Oromiya, 20.3% in Tigray and 13.4% in SNNP regions. The major diseases encountered include rusts, septoria leaf blotches, foot and root diseases, Fusarium head blight and smuts. The overall mean prevalence of stem rust was 61%, yellow rust 22%, leaf rust 18.8% and Septoria leaf blotches 52.9%. The incidence of the important diseases was highest in SNNP region. The mean incidence of yellow rust ranged from 5.7% in Oromiya to 39.2% in SNNP. The lowest incidence of stem rust, 15.9%, was noted in Tigray and the highest, 64.4%, in SNNP. The minimum mean Septoria incidence was 23% in Oromiya, and maximum was 66.7% in SNNP. Stem rust severities varied from 7 MR-MSS in Tigray to 36 MR-MSS in SNNP. Furthermore, the widely grown varieties Digelu and Danda’a were resistant to yellow rust, but susceptible to stem rust. Varieties Meda Wolbu, Hogona and Ogolcho were not affected by any of the rusts in Oromiya. Variety Hidase was susceptible in SNNP. Out of 115 Pgt cultures established from stem rust samples collected from the three regions, races TKTTF, RRTTF, TTKSK, TRTTF and JRCQC were identified. Stem rust samples were collected from varieties Digelu, Danda’a, Kakaba, and Hidase. Race TKTTF, virulent on Digalu and first identified in Oromiya region in 2013, is now present in all areas. Adapted varieties with durable stem rust resistance in Ethiopia remains an urgent requirement.
Primary Author: Woldeab, Ambo Plant Protection Research Center, Ethiopia
Keywords: Ethiopia, wheat diseases
Resistance offers the best means of control of the cereal rusts, but must be strategically deployed so as to avoid exposure of single major genes, which have faltered so many times in the past. The pyramiding of multiple effective resistance genes is a strategy that has proven effective in a number of wheat production areas around the world. However, the process of incorporating multiple resistance genes into a single cultivar using standard breeding techniques is time consuming, laborious, and hampered by the problem of linkage drag. If a suite of effective resistance genes could be efficiently cloned and transferred into wheat as a cassette, it would accelerate the development of durably resistant varieties without the problem of linkage drag. Toward this end, we have developed a resistance gene cloning technology based on resistance gene enrichment sequencing (RenSeq) of EMS-derived mutant R gene alleles. As a proof of concept test, we successfully ‘re’-cloned the already characterized gene Sr33 and are now targeting the cloning of eight other effective resistance genes. For the identification of susceptible mutants for the cloning of Sr32 from Aegilops speltoides, we screened 1,109 M2 families with race TPMKC — as a surrogate for race TTKSK. Five susceptible M2 mutants were confirmed by progeny testing. These mutants were also susceptible to race TTKSK. For the population involving Sr1644 from Ae. sharonensis, 1,649 M2 families were screened, yielding 33 M2 families that appeared to segregate for susceptibility. Thirteen of 33 families were confirmed as bona fide susceptible mutants by progeny tests in the M3 generation. Identification of susceptible EMS mutants of Sr32 and Sr1644 suggests that the underlying resistance in these lines is conferred by single genes. We will report on progress to clone and characterize these genes using R gene exome capture and sequencing technology (RenSeq).
Primary Author: Wulff, John Innes Centre, UK
Keywords: resistance, cloning, pyramiding
Stripe rust of wheat, caused by Puccinia striiformis f. sp. tritici, continues to cause severe damage worldwide. Durable resistance is a key for sustainable control of the disease. High-temperature adult-plant (HTAP) resistance, which expresses when the weather becomes warm and plants grow old, has been demonstrated to be durable. We have conducted numerous of studies for understanding molecular mechanisms of different types of stripe rust resistance using a transcriptomics approach. Through comparing gene expression patterns with racespecific, all-stage resistance controlled by various genes, we found that a greater diversity of genes is involved in HTAP resistance. The genes involved in HTAP resistance are induced more slowly and their expression induction is less dramatic than genes involved in all-stage resistance. The high diversity of genes and less dramatic expression induction may explain the durability and incomplete level of HTAP resistance. Identification of transcripts may be helpful in identifying resistance controlled by different genes and in selecting better combinations of genes for pyramiding to achieve adequate and more durable resistance.
Primary Author: Xianming Chen, USDA-ARS Wheat Genetics, Quality, Physiology and Disease Research Unit, Pullman, WA
Keywords:
Ug99 is a devastating race of Puccinia graminis f.sp. tritici possessing virulence against resistant genes Sr31 and Sr24. This race is highly adoptive and has spread quite rapidly with 13 known variants covering 13 different countries. For reducing the vulnerability of wheat in south Asia to the Ug99, breeding durable resistant varieties is important. India, second largest wheat producer, falls in the predicted pathway of Ug99. Most of the Indian germplasm possesses Sr31 and Sr24 in their background. HUW468, a well adopted variety of north eastern plains zone (NEPZ) of India, carries durable resistance gene Sr2. To strengthen it, a MABB program was initiated to introgressed two major genes (Sr50 and SrWeb) using a donor line PMBWIR4 from CIMMYT. The foreground selection was performed with Xgwm47 for SrWeb and IB267 for Sr50 followed by the background selection by using 128 polymorphic SSR markers covering all chromosomes. Backcross progenies of HUW468 were screened in the field condition by using of Pgt race 21A-2 at IARI, Regional Station, Indore located in the central India. Superior selected lines from BC2F4:5 generation was planted at three locations in India namely; Varanasi, Indore and Dharwad. HUW468-09-25-47-09 and HUW468-09-25-47-56 were selected from BC2F5 generation having Sr50 and SrWeb along with Sr2 gene, superior agronomic performance and with 93.5% and 92.7% genome recovery, respectively. These two lines also possess 6-10 % yield superiority over the recipient parent HUW468. These lines have been submitted for registration in NBPGR (National Bureau of Plant Genetic Resources), India.
Primary Author: Yadav, Institute of Agricultural Sciences, Banaras Hindu University, Varanasi 221005, India
Keywords: stem rust
Wheat is grown in Syria during the November-December. Wheat is exposed to many strains that negatively affect its productivity especially rust diseases, which was reported on wheat in Syria for many years and the most severe in 2010, Therefore, we studied the effect of planting dates on the severity and development of yellow rust disease. Where the field trials of the 2010-2011 season were carried out at the two locations in northeastern of Syria: Al-Qamishli Research Center and Yanbouh Research Station in Al-Malekia. By cultivating the susceptible bread wheat Cham 8, where six dates were planted starting from 02.10. 2010, a difference of 15 days. The results showed there was a difference in the severity of the yellow rust disease according to the dates of cultivation and thus the stages of growth in the plant and this was evident in the Yanbouh location where the onset of the onset of injury on 08.04.2011 in the all dates and developed the infection to 40S degrees and 30%. Also, on the 24. 04. 2011, the infection was recorded at the Qamishli location only on the third and fourth dates. The disease did not develop more than 10S and 10% due to climatic conditions due to rain and high temperature during the season. The results showed a positive correlation between the evolution of the disease and vegetative growth of plants, where the growth of plants was more active at the site of Yanbouh, especially in the second, third and fourth dates in the development of infection on plants in the rest of the dates because of weak and slow growth of plants.
Primary Author: Youssef, University of Hohenheim, Germany
Keywords:
A number of stem rust resistance genes derived from wild relatives of wheat appeared to be more effective against race TTKSK (Ug99) of Puccinia graminis f. sp. tritici than Sr genes of wheat origin. In an attempt to identify sources of stem rust resistance genes effective against TTKSK, we evaluated several cultivated and wild relatives of wheat for resistance to TTKSK and other stem rust races with broad virulence in seedling tests. Preliminary results indicated that TTKSK resistance could readily be found, but frequencies of resistance varied among the species. Aegilops speltoides had the highest frequency of resistance (nearly 100%). Other species having high frequencies of TTKSK resistance included triticale (77.7% of 567 accessions), Triticum urartu (96.8% of 205 accessions), and T. monococcum (61% of 1020 accessions). Frequencies of TTKSK resistance in other species were: 14.7% in Ae. tauschii (456 accessions), 15% in T. timopheevii (298 accessions), and 17% in T. turgidum ssp. dicoccoides (157 accessions). Based on specific infection types to several races, we postulated that novel genes for resistance to TTKSK are present in some of these species. Accessions with putatively new resistance genes were selected to develop crosses for introgressing resistance into wheat and for developing mapping populations.
Primary Author: Yue Jin, USDA-ARS, Cereal Disease Laboratory
Keywords:
