Wheat is one of the world's most important crops. It provides as much as one-fifth of daily global calorie intake and, for the major wheat-growing nations, like Canada, with wheat exports of $7 billion a year, it's also a major economic driver.
The dietary and economic importance of wheat has grown dramatically over the past 100 years, thanks in large part to breeding programs that have developed new, hardier and higher-yielding varieties. At the National Research Council of Canada's (NRC) Aquatic and Crop Development Research Centre in Saskatoon, Research Officer Dr. Wentao Zhang says improvement must continue if the nutritional needs of an ever-growing global population are to be satisfied. Developing varieties that are more productive is only part of the challenge.
We also need varieties that can thrive in our increasingly erratic climatic conditions, and that are resistant to diseases that can devastate a crop," explains Dr. Zhang. "Restoring some of the lost genetic diversity in wheat is an important part of that."
The diversity challenge
Dr. Zhang explains that, over decades of breeding, modern wheat varieties have become less and less genetically diverse. "As a result, for example, many varieties rely on the same genetic resistance to serious diseases such as fusarium head blight," says Dr. Zhang. "So, if that resistance should break down in one variety of wheat, many other varieties would also be at risk."
With funding support from the Government of Canada's Genomics Research and Development Initiative (GRDI), Dr. Zhang and NRC Technical Officer Christine Sidebottom have provided Canadian wheat breeders with an important new tool to support their efforts to meet this challenge—the Canadian Wheat Nested Association Mapping Population, or CanNAM.
With CanNAM, breeders, researchers and others have access to extensive genetic information on thousands of lines of wheat that represent a virtually complete history of wheat breeding in Canada—and then some.
To create CanNAM, Dr. Zhang and Ms. Sidebottom took a successful, modern Canadian variety of wheat called Stettler, and crossed it with 25 other Canadian elite varieties developed over the past 100 years or so. To further enhance genetic diversity, they also crossed Stettler with 25 synthetic varieties of wheat, which are themselves the result of crossing modern varieties with wheat's wild relatives. (They're called "synthetic" because today's wheat and its ancient ancestors are now so distantly related, they can't mate successfully without some help in the laboratory).
A painstaking process
"Those initial crosses gave us 50 sub-populations," explains Dr. Zhang. "We planted seeds from those plants, grew them to maturity, then took 100 seeds from each of those 50 plants, and grew them to maturity, giving us 100 plants from each of the original 50 crosses.
"We then took one seed from each of those 5,000 plants, grew them to maturity, took one seed from each of those 5,000 and so on to an eighth generation to ensure consistency in the genetic makeup of each of the 100 lines we'd grown from the first 50 sub-populations we created—5,000 lines altogether."
Still more work
Growing several generations of thousands of plants from seed was just the beginning. As Ms. Sidebottom explains: "At this point, we just had a lot of plants. We still needed a cost-effective way to identify where the genetic information of interest could be found in each of the 5,000 lines we'd developed. In fact, this was the whole point of the project."
We settled on a genomics method called exome capture sequencing, which allowed us to identify the informative regions of the genome of each of the 5,000 lines," says Ms. Sidebottom. "That is, for each line, we've identified the region of its genome where genes controlling different, specific traits are located."
A significant resource
Dr. Andrew Sharpe, a former NRC scientist who has been involved in the GRDI in the past, says CanNAM is a significant resource for wheat breeders and researchers alike.
"This is a lot of important genetic information in one place, and organized so that breeders can scan data for thousands of lines of wheat and determine fairly quickly which of them may offer the traits in which they're interested," says Dr. Sharpe, now Director of Genomics and Bioinformatics at the Global Institute for Food Security at the University of Saskatchewan.
"On top of that, by including these synthetic varieties, CanNAM gives breeders access to a much more diverse catalogue of genetic information. Breeders looking for new resistance to a particular disease, for example, can identify the section of the genome associated with that trait in individual plants from the thousands of lines in the population.
"If they come across something new or different in one line, they can scan related lines for similar genetic profiles, assess whether other valuable traits are also represented in those lines, and decide from there which lines they might want to incorporate into their breeding program."