Posts Tagged ‘wheat genomics’

New genetic analysis advances the global quest for yellow rust resistant wheat

A wheat leaf infected with yellow rust, also known as stripe rust. Photo: Thomas Lumpkin/CIMMYT

Yellow rust, also known as stripe rust, is a tenacious and widespread fungal disease that threatens wheat all over the world. The fungal pathogen that causes the rust — Puccinia striiformis — is prevalent in more than 60 countries, and an estimated 88% of the world’s wheat production is considered vulnerable, with up to 100% losses. 

A number of factors – including favorable weather conditions, the adaptation of existing races and emergence of new ones, and a changing climate – have caused a recent uptick in severe outbreaks. Farmers can use fungicides and farming management practices to battle the fungus, but sowing resistant seeds is widely considered as the most cost-effective, environmentally-safe and sustainable way to beat it.

A new analysis by wheat scientists at the International Maize and Wheat Improvement Center (CIMMYT) published in Scientific Reports provides valuable insights and a deep resource of genetic information to increase the speed and accuracy of efforts to breed yellow rust resistant wheat.

To understand the shared genetic basis of yellow rust resistance over time and in three geographic regions, CIMMYT scientists performed a large genome-wide association study leveraging a dataset of 43,706 observations on 23,346 wheat lines evaluated between 2013 and 2019 at sites in India, Kenya and Mexico.

Photo: Flickr/ Wheat Genetics Lab

They found more than 100 repeatable –that is, statistically significant in multiple datasets — genome-wide markers associated with yellow rust that aligned to the reference genome of wheat.

 “These findings represent a significant advancement in our knowledge about the genetics of yellow rust resistance in bread wheat and provide exciting opportunities for designing future genomics-based breeding strategies for tackling yellow rust,” said CIMMYT wheat scientist Philomin Juliana, the lead author of the paper.

CIMMYT wheat scientists have been breeding for yellow rust resistance since the early 1970s. Breeding for resistance is a painstaking process involving crossing parents with slow rusting genes, selecting early-generation plants which exhibit resistance in Toluca, Mexico, and then subjecting the advanced generations to intense screening in sites like Karnal (in collaboration with the Indian Institute of Wheat and Barley Research) and Ludhiana (in collaboration with the Borlaug Institute for South Asia) in India; Njoro in Kenya; and Celaya (in collaboration with the Instituto Nacional de Investigaciones Forestales, Agricolas y Pecuarias), El Batan and Toluca in Mexico. Identifying genes related to resistance can increase the efficiency of this selection process, giving breeders a head start by allowing them to begin the crossing process with varieties that are more likely to have resistance genes.

In the study, the wheat scientists also conducted “allelic fingerprinting” on the largest panel of wheat breeding lines to date — 52,067 lines, genomically characterizing them for yellow rust resistance.  The resulting data creates opportunities using molecular markers to identify varieties with desired combinations of resistance genes.

“This information advances our knowledge on the genetics of yellow rust resistance in thousands of wheat lines, and has important implications for the future design of resistant crosses and varieties,” Juliana said.

Overall, the markers and fingerprints identified in this study are a valuable resource not only for CIMMYT breeders but also for the global wheat breeding community in its efforts to accelerate yellow rust resistance breeding.

This work was made possible by the generous support of the Delivering Genetic Gain in Wheat (DGGW) project funded by the Bill & Melinda Gates Foundation and the UK  Department for International Development (DFID) and managed by Cornell University; the U.S. Agency for International Development’s Feed the Future Initiative; and the genotyping support of Dr. Jesse Poland from the innovation lab at Kansas State University.

Read the full article here:
https://doi.org/10.1038/s41598-020-67874-x

Juliana, P., Singh, R.P., Huerta-Espino, J. et al. 2020. “Genome-wide mapping and allelic fingerprinting provide insights into the genetics of resistance to wheat stripe rust in India, Kenya and Mexico.” Nature Scientific Reports.

Harnessing the potential of state-of-the-art genomic technologies for accelerating the rate of genetic gain in wheat

This blog by Philomin Juliana was originally published on the Borlaug Global Rust Initiative website.

Genomic breeding technologies offer exciting opportunities for wheat improvement amidst escalating challenges like changing climates, unpredictable temperatures, reduced precipitation and biotic stresses. Recognizing the need for accelerating the rate of genetic gain in wheat, the Delivering Genetic Gain in Wheat and the USAID Feed the Future projects have contributed extensively to the phenotyping and genotyping of an impressive number of 74,403 CIMMYT wheat breeding lines, generating more than a million phenotyping datapoints and 3 billion marker datapoints. These big datasets have been leveraged for evaluating state-of-the-art genomic technologies like genomic selection, genome-wide association mapping, and genomic fingerprinting that have empowered the CIMMYT wheat breeding program to efficiently deliver high-yielding, climate resilient and disease resistant varieties.

Genomic selection, a genomics-based selection strategy where genomic-estimated breeding values obtained from genome-wide molecular markers are used for the selection of individuals has gained burgeoning interest in recent years and is advocated as an approach that can dramatically accelerate genetic gains and change the role of phenotyping in breeding. Since it can be beneficial for CIMMYT and other wheat breeding programs, particularly in developing countries that are constrained in their ability to evaluate a large number of breeding lines due to limited resources, we have done a comprehensive evaluation of genomic selection for 35 key traits in wheat evaluated by CIMMYT and national partners.

Our results have provided strong evidence that genomic selection will be a very powerful tool for end-use quality related traits like alveograph, mixing time, grain protein, flour yield, flour sedimentation, loaf volume etc. and some diseases, that were well predicted using historic training populations. Hence, genomic estimated breeding values for these traits have been routinely integrated into selection decisions and selections have been scaled up to un-phenotyped early-generations using predicted values. This has led to a paradigm shift in integrating genomic breeding tools into CIMMYT’s wheat breeding pipeline and has resulted in better selection efficiency and high phenotyping cost-savings to the program.

We have also explored several genomic selection implementation scenarios for grain yield and determined the prospects of using genomic selection for minimizing the number of lines, years and sites tested by borrowing information from relatives, correlated years and sites. For this, we leveraged a large dataset of 61,064 grain yield observations from 1,974 yield trials evaluated by CIMMYT and national partners at 100 locations in 34 countries including Afghanistan, Algeria, Angola, Argentina, Bangladesh, Canada, Chile, China, Egypt, Ethiopia, Greece, India, Iran, Iraq, Libya, Mexico, Morocco, Myanmar, Nepal, Nigeria, Pakistan, Paraguay, Portugal, South Africa, Spain, Sudan, Taiwan, Tanzania, Tunisia, Turkey, Ukraine, Venezuela, Zambia and Zimbabwe. We also applied a quantitative genetics framework to explore the relationships between grain yield predictabilities and estimated heritabilities, variance components, phenotypic and genetic correlations for grain yield evaluated in different environments, all of which provided substantial insights into the challenges of predicting grain yield and the prospects for designing future genomic selection schemes.

We also performed a large genome-wide association study that led to a significant breakthrough in understanding the genetic-architecture of key traits like phenology, plant height, lodging, resistance to rusts and other foliar diseases, grain color, kernel weight, dough strength, bread-making quality, protein content and grain yield in wheat. We have identified hundreds of significant marker-trait associations and delineated 142 unique linkage-based QTLs, among which 55.6% were novel. One of the extremely intriguing and novel co-locations identified in our study was the association of the 2NS translocation from Aegilops ventricosa with grain yield in 10 different environments, stem rust seedling resistance to many races, stripe rust in Mexico, wheat blast, and lodging, demonstrating its remarkable value for wheat breeding. We also anchored about 542 significant trait-associated markers and 118 previously reported genes in proximity to the significant markers onto a powerful reference phenotype-genotype map aligned to the refence genome of bread wheat, which is a valuable resource providing new opportunities for accelerating genomics-assisted wheat breeding through a targeted selection of desired regions.

We have fingerprinted 44,624 wheat lines for 195 traits-associated markers, generating over 7.6 million data-points, which is a phenomenal resource to the global wheat community for enhancing productivity and stress-resilience in wheat. The fingerprinted panel comprises several key varieties cultivated worldwide, parents from CIMMYT’s crossing blocks 2009-2018 and is a quantum leap in understanding the genetic basis of traits in superior varieties. For example, a benchmark high-yielding CIMMYT-derived Mexican variety, BORLAUG100 F2014 was found to be rich in grain yield favorable alleles and a key stem rust QTL against the Ug99 lineage was traced back to old Kenyan (Kenya Fahari, Kenya Swara) and Ethiopian (FH6-1-7) varieties.

Furthermore, we also examined the marker allele frequency dynamics for key traits over 15 years to characterize the role of selection at CIMMYT in shaping patterns of allelic variation over time. While there was a spectacular increase in favorable allele frequencies for many traits over years due to selection, the results also emphasized the need for a continued effort to introduce novel sources of favorable alleles and the importance of integrating genomic tools in achieving accelerated enrichment of favorable alleles. Overall, our research has facilitated extending the frontiers of genomics-assisted breeding in wheat and will be very beneficial for future diagnostic marker development, gene discovery, marker-assisted selection and genomic selection in wheat.

Philomin Juliana’s 5 May 2020 seminar is here.

New publications: Special collection on wheat genetics and breeding

Researchers present highlights from 40 years of collaboration on wheat genomics, breeding for disease resistance and quality improvement.

This article by Emma Orchardson was originally posted on the CIMMYT website.

Wheat rust expert Bob McIntosh, of the Plant Breeding Institute, University of Sydney, Australia, examining rust symptoms on a wheat line in the field at the Kenya Agricultural Research Institute’s (KARI) Njoro research station in Kenya. Photo: CIMMYT/Petr Kosina

Global wheat production is currently facing great challenges, from increasing climate variation to occurrence of various pests and diseases. These factors continue to limit wheat production in a number of countries, including China, where in 2018 unseasonably cold temperatures resulted in yield reduction of more than 10% in major wheat growing regions. Around the same time, Fusarium head blight spread from the Yangtze region to the Yellow and Huai Valleys, and northern China experienced a shortage of irrigated water.

In light of these ongoing challenges, international collaboration, as well as the development of new technologies and their integration with existing ones, has a key role to play in supporting sustainable wheat improvement, especially in developing countries. The International Maize and Wheat Improvement Center (CIMMYT) has been collaborating with China on wheat improvement for over 40 years, driving significant progress in a number of areas.

Notably, a standardized protocol for testing Chinese noodle quality has been established, as has a methodology for breeding adult-plant resistance to yellow rust, leaf rust and powdery mildew. More than 330 cultivars derived from CIMMYT germplasm have been released in the country and are currently grown over 9% of the Chinese wheat production area, while physiological approaches have been used to characterize yield potential and develop high-efficiency phenotyping platforms. The development of climate-resilient cultivars using new technology will be a priority area for future collaboration.

In a special issue of Frontiers of Agricultural Science and Engineering focused on wheat genetics and breeding, CIMMYT researchers present highlights from global progress in wheat genomics, breeding for disease resistance, as well as quality improvement, in a collection of nine review articles and one research article. They emphasize the significance of using new technology for genotyping and phenotyping when developing new cultivars, as well as the importance of global collaboration in responding to ongoing challenges.

In a paper on wheat stem rust, CIMMYT scientists Sridhar Bhavani, David Hodson, Julio Huerta-Espino, Mandeep Randawa and Ravi Singh discuss progress in breeding for resistance to Ug99 and other races of stem rust fungus, complex virulence combinations of which continue to pose a significant threat to global wheat production. The authors detail how effective gene stewardship and new generation breeding materials, complemented by active surveillance and monitoring, have helped to limit major epidemics and increase grain yield potential in key target environments.

In the same issue, an article by Caiyun Lui et al. discusses the application of spectral reflectance indices (SRIs) as proxies to screen for yield potential and heat stress, which is emerging in crop breeding programs. The results of a recent study, which evaluated 287 elite lines, highlight the utility of SRIs as proxies for grain yield. High heritability estimates and the identification of marker-trait associations indicate that SRIs are useful tools for understanding the genetic basis of agronomic and physiological traits.

Other papers by CIMMYT researchers discuss the history, activities and impact of the International Winter Wheat Improvement Program, as well as the ongoing work on the genetic improvement of wheat grain quality at CIMMYT.

Find the full collection of articles in Frontiers of Agricultural Science and Engineering, Volume 6, Issue 3, September 2019.