Posts Tagged ‘wheat yield’

Publication summary: Retrospective Quantitative Genetic Analysis and Genomic Prediction of Global Wheat Yields

A new quantitative genetics study makes a strong case for the yield testing strategies the International Maize and Wheat Improvement Center (CIMMYT) uses in its wheat breeding program.

Wheat fields at CIMMYT’s Campo Experimental Norman E. Borlaug (CENEB) in Ciudad Obregón. Photo: CIMMYT.

The process for breeding for grain yield in bread wheat at the International Maize and Wheat Improvement Center (CIMMYT) involves three-stage testing at an experimental station in the desert environment of Ciudad Obregón, in Mexico’s Yaqui Valley. Because the conditions in Obregón are extremely favorable, CIMMYT wheat breeders are able to replicate growing environments all over the world, and test the yield potential and climate-resilience of wheat varieties for every major global wheat growing area. These replicated test areas in Obregón are known as selection environments (SEs).

This process has its roots in the innovative work of wheat breeder and Nobel Prize winner Norman Borlaug, more than 50 years ago.  Wheat scientists at CIMMYT, led by wheat breeder Philomin Juliana, wanted to see if it remained effective.

The scientists conducted a large quantitative genetics study comparing the grain yield performance of lines in the Obregón SEs with that of lines in target growing sites throughout the world. They based their comparison on data from two major wheat trials: the South Asia Bread Wheat Genomic Prediction Yield Trials in India, Pakistan and Bangladesh initiated by the U.S. Agency for International Development Feed the Future initiative, and the global testing environments of the Elite Spring Wheat Yield Trials.

The findings, published in Retrospective Quantitative Genetic Analysis and Genomic Prediction of Global Wheat Yields, in Frontiers in Plant Science, found that the Obregón yield testing process in different SEs is very efficient in developing high-yielding and resilient wheat lines for target sites.

The authors found higher average heritabilities, or trait variations due to genetic differences, for grain yield in the Obregón SEs than in the target sites (44.2 and 92.3% higher for the South Asia and global trials, respectively), indicating greater precision in the SE trials than those in the target sites.   They also observed significant genetic correlations between one or more SEs in Obregón and all five South Asian sites, as well as with the majority (65.1%) of the Elite Spring Wheat Yield Trial sites. Lastly, they found a high ratio of selection response by selecting for grain yield in the SEs of Obregón than directly in the target sites.

“The results of this study make it evident that the rigorous multi-year yield testing in Obregón environments has helped to develop wheat lines that have wide-adaptability across diverse geographical locations and resilience to environmental variations,” said Philomin Juliana, CIMMYT associate scientist and lead author of the article.

“This is particularly important for smallholder farmers in developing countries growing wheat on less than 2 hectares who cannot afford crop losses due to year-to-year environmental changes.”

In addition to these comparisons, the scientists conducted genomic prediction for grain yield in the target sites, based on the performance of the same lines in the SEs of Obregón. They found high year-to-year variations in grain yield predictabilities, highlighting the importance of multi-environment testing across time and space to stave off the environment-induced uncertainties in wheat yields.

“While our results demonstrate the challenges involved in genomic prediction of grain yield in future unknown environments, it also opens up new horizons for further exciting research on designing genomic selection-driven breeding for wheat grain yield,” said Juliana. 

This type of quantitative genetics analysis using multi-year and multi-site grain yield data is one of the first steps to assessing the effectiveness of CIMMYT’s current grain yield testing and making recommendations for improvement—a key objective of the new Accelerating Genetic Gains in Maize and Wheat for Improved Livelihoods (AGG) project, which aims to accelerate the breeding progress by optimizing current breeding schemes.

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 Foreign, Commonwealth & Development Office (FCDO) and managed by Cornell University; the U.S. Agency for International Development’s Feed the Future initiative; and several collaborating national partners who generated the grain yield data.

Read the full article here: https://doi.org/10.3389/fpls.2020.580136

A fresh look at the genes behind grain weight in spring bread wheat

New study provides an extensive field-test validation of existing genetic markers for thousand grain weight; finds both surprises and promising results

To meet the demand for wheat from a rising and quickly urbanizing population, wheat yields in farmers’ fields must increase by an estimated 1.5% each year through 2030. 

Of all the factors that influence yield, grain weight is the trait that is most stable and heritable for use in breeding improved wheat varieties.  Breeders measure this by thousand grain weight (TGW).

Over the years, molecular scientists have made efforts to identify genes related to increased TGW, in order to speed up breeding through marker-assisted selection (MAS). Using MAS, breeders can select parents that contain genes related to the traits they are looking for, increasing the likelihood they will be passed on and incorporated in a new variety. 

Guillermo Garcia Barrios, a co-author of the study and student at Colegio de Postgraduados in Montecillo, Mexico with a PHERAstar machine used to validate genetic markers.
Photo: Marcia MacNeil/CIMMYT

There have been some limited successes in these efforts: in the past years, a few genes related to increased TGW have been cloned, and a set of genetic markers have been determined to be used for MAS. However, the effects of most of these candidate genes (CGs) have not yet been validated in diverse sets of wheat germplasm throughout the world that represent the full range of global wheat growing environments.

A group of wheat geneticists and molecular breeders from the International Maize and Wheat Improvement Center (CIMMYT) has recently conducted a thorough study to confirm the effects of the favorable alleles reported for these genes on TGW in CIMMYT wheat,   — and to identify new genetic determinants of this desired trait.

They found some good news and some bad.

First, the good news:  focusing on more than 4000 lines of CIMMYT wheat germplasm they found 15 haplotype blocks significantly associated with TGW.  Four haplotype blocks associated with TGW were also associated with grain yield – a grand prize for breeders, because in general the positive association of grain yield with TGW is less profound and sometimes even negative. However, of the 14 genes that had been previously reported to increase TGW, only one in CIMMYT’s 2015-2016 Elite Yield Trial and two in Wheat Associative Mapping Initiative panel were shown to have significant TGW associations.

The scientists also found that the alleles — pairs of genes on a chromosome that determine heredity – that were supposedly favorable to TGW actually decreased it.   These candidate genes also appear to vary in their TGW effects with genetic background and/or environment.

Thus, these findings also provide a foundation for more detailed investigations, opening the door for more studies on the genetic background dependence and environment sensitivity of the known candidate genes for TGW. 

Thousand Gain Weight is measured in this machine at CIMMYT’s administrative headquarters at El Batan, Mexico.
Photo: Marcia MacNeil/CIMMYT

 “Our findings indicate that it will be challenging to use MAS based on these existing markers across individual breeding programs,” said Deepmala Sehgal, CIMMYT wheat geneticist and the primary author of the study.

However, efforts to identify new genetic determinants of TGW were promising.  The authors’ study of CIMMYT germplasm found one locus on chromosome 6A that showed increases of up to 2.60 grams in TGW and up to 258 kilograms per hectare in grain yield.

This discovery expands opportunities for developing diagnostic markers to assist in multi-gene pyramiding – a process that can derive new and complementary allele combinations for enhanced wheat TGW and grain yield.

Most of all, the study highlights the strong need for better and more validation of the genes related to this and other traits, so that breeders can be sure they are using material that is confirmed to increase wheat grain weight and genetic yield.

“Our findings are very promising for future efforts to efficiently develop more productive wheat in both grain weight and grain yield,” said Sehgal. “This ultimately means more bread on household tables throughout the world.”

 “Validation of Candidate Gene-Based Markers and Identification of Novel Loci for Thousand-Grain Weight in Spring Bread Wheat” in Frontiers in Plant Science by Deepmala Sehgal, Suchismita Mondal, Carlos Guzman, Guillermo Garcia Barrios, Carolina Franco, Ravi Singh and Susanne Dreisigacker was supported by funding from the CGIAR Research Program on Wheat (WHEAT), the Delivering Genetic Gain in Wheat (DGGW) project funded by the Bill & Melinda Gates Foundation and the UK Department for International Development (DFID), and the US Agency for International Development (USAID) Feed the Future Innovation Lab for Applied Wheat Genomics.

Read the full article here: https://doi.org/10.3389/fpls.2019.01189


Wheat grains prepared for placement in TGW machine. Photo: Marcia MacNeil/CIMMYT