Researchers are discovering new genes to increase tolerance to disease and environmental stress.
Disease and environmental stress were present in abundance last year, thanks to some extreme weather conditions in the United States and Canada. The U.S. Midwest experienced record-breaking temperatures and serious drought, while it was the third wettest and fifth warmest spring in sixty-five years across the Canadian Prairies, followed by one of the ten hottest summers on record.
Heat and humidity increased the incidence of disease, causing an unusually high number of aster yellows outbreaks in canola and cereals, blackleg and clubroot in canola, and severe fusarium head blight outbreaks in cereals.
It’s hardly surprising that there is a renewed focus on efforts to provide farmers with tools to combat the disease and environmental stresses that are affecting their crops.
Benefits of Wild Relatives
While genomics has accelerated the process of identifying individual genes and evaluating them for the attributes they confer on plants, conventional breeding is also advancing the development of varieties with specific traits such as disease resistance and stress tolerance. Researchers are increasingly turning to the wild relatives of plants for answers to these complex issues. “You might be able to identify genes in wild relatives that can be integrated into the crop, or using a biotech approach, inserting genes that would be helpful,” says Wilf Keller, president and CEO of Ag West Bio Inc. in Saskatoon. “For example, rye has more tolerance to frost and cold than wheat does, and it’s possible to cross wheat and rye, so we may ultimately be able to move genes from rye to wheat.”
There are several seed companies that are at the forefront of developing stress tolerant crops, especially in corn, where drought tolerant varieties are widely available. However, researchers have come to realize that they need to expand their search beyond the obvious to build robust resistance or tolerance into new varieties.
It’s often a combination of genes, not just related to abiotic stresses like drought, heat or cold, which interact with each other to confer stress tolerance. Ravindra Chibbar, Canada research chair at the University of Saskatchewan, has been studying low temperature tolerance and winter survival in winter wheat. Chibbar and his team sequenced a chromosome region of a very cold hardy winter wheat, cultivar Norstar, and identified transcription factors, or regulatory genes, which can induce changes in other genes. From there, they identified and characterized a handful of genes responsible for enhanced cold hardiness in winter wheat.
The research, however, also uncovered a relationship with other developmental traits, such as growth habit and final leaf number, which also contribute to a plant’s cold tolerance. “The contribution of the developmental traits is a major advancement from our work that has come by identifying wheat chromosomal regions contributing to cold tolerance,” says Chibbar.
Environmental stress varies according to geography and season, adding complexity to the task of incorporating traits that help producers cope with unpredictable weather. “We are selecting for germplasm that performs well across a lot of environments and will offer some tolerance to those high stress environments,” says Chris Anderson, canola breeding lead for Monsanto Company.
Driving Disease Research
Over the past couple of decades, producers have come to rely on varieties with resistance to various diseases, but increasingly the single genes conferring resistance are starting to show signs of being overtaken by pathogens that have adapted to this type of resistance. In addition, agricultural practices such as short rotations and, in some cases, an over-reliance on fungicides, are driving researchers to seek out multiple sources of resistance.
“We are focused not just on delivering disease resistance today, but also on finding new resistance genes and bringing them into elite germplasm,” says Anderson. “We are spending a lot of effort [to determine] how to bring those genes together to create more robust tolerance—tolerance that should stand up in the environment longer.”
Much of the current public research is focused on gaining a deeper understanding of the pathogens and their variability. Key steps in that process are characterizing, at the molecular level, the different types of resistance that are present and determining how pathogens adapt to resistance across larger geographies.
One such research project is being led by Kelly Turkington, a research scientist at Agriculture and Agri-Food Canada’s Lacombe Research Centre, and also involves researchers from the University of Alberta, Alberta Agriculture, and AAFC scientists from Manitoba and Saskatchewan. The project is assessing variability in the net blotch pathogen in relation to mating type, sexual reproduction, host resistance and sensitivity to fungicides. “We wanted to look at the pathogen in the sense of how variable it was across the Prairie region,” says Turkington, “and that has implications for how rapidly it could potentially adapt to sources of resistance that are deployed by breeders.”
“Doubled haploid production shaves years off [the breeding process], and if you can use greenhouse and contra season production as well, you can save three or four years quite quickly.” —Todd Hyra
Speeding Up the Process
Both public and private breeding programs are constantly seeking ways to deliver disease and stress resistant varieties more quickly to producers.
Contra season production, where seed is multiplied during the winter in the southern United States or elsewhere, such as in Southern Hemisphere nations, is common in higher value, lower volume crops such as canola and corn, but isn’t as easy to do with cereals. “In cereals, it has to be done quite cautiously,” says Todd Hyra, Western Canada business manager for SeCan. “You have to really pick your spot because you have to do those [crops] at the beginning of multiplication, rather than at the end because the volumes get so large, so fast. You really need to be producing those final years of multiplication in Canada in order to make the economics work.”
Doubled haploid production is another important technology that is being used to speed up the development of new varieties. Traditional techniques generally require multiple generations of selection to stabilize desired traits in breeding lines, which eventually become new varieties. Doubled haploids, on the other hand, are genetically pure inbred plants. Through the use of biotechnology, these plants are produced in a single year, enabling breeders to stabilize desired traits in just one generation. “Doubled haploid production shaves years off [the breeding process], and if you can use greenhouse and contra season production as well, you can save three or four years quite quickly,” says Hyra.
Rising Interest
Epigenetics is a scientific discipline that has been around for some time, but thanks to related high-profile research into human health, it is gaining more attention in plant research circles. A team led by scientists Jeannie Gilbert and Steve Haber at AAFC’s Cereals Research Centre in Winnipeg has been exploring the potential of epigenetics to deliver adapted, high-quality spring wheat germplasm, which combines new resistance to some pathogens while maintaining existing resistance to others.
“We have a sister breeding group in Europe and it’s a tremendous opportunity to share information and germplasm back and forth to utilize the best tools that we can.” —Chris Anderson
“The starting materials for our work are contemporary, high-quality wheat cultivars that are well adapted to Western Canada,” says Haber. “They are resistant to predominant races of leaf and stem rust, but fully susceptible to wheat streak mosaic virus and range in responses to fusarium head blight from highly susceptible to, at best, moderately resistant.”
In other words, epigenetics affects the expression of the information coded in the genes of plants and other living organisms. These heritable changes in gene expression in the plant are achieved without changing the coding information in the DNA, and do not involve the insertion of outside or exotic genes.
“Our protocols evolve, among the direct descendants of these cultivars, lines with near-immunity to WSMV, and with repeated selection, lines with improved resistance to FHB and leafspot diseases,” says Haber.
Many Hands, Light Work
Private companies have had much success delivering new varieties possessing agronomic advantages such as increased yield and traits, which provide a good return on investment as well as value for producers. The public sector has also conducted research into plant diseases for many years, resulting in a large reservoir of knowledge and expertise within public laboratories and universities.
Increasingly, these areas of expertise are being brought together as domestic and international partnerships and collaborations between private, public and non-profit entities. “Disease [research] is a very good area for public-private partnerships,” says Keller. “I think we are seeing more of it, and I think we will see even more because it makes very good sense for these two different groups to work with each other.”
Large-scale screening for resistance is becoming more common and involves collaborations between international breeding facilities, which share information and germplasm.
A research program into net blotch in cereals involves researchers from Canada and Australia, who are testing the reaction of Australian barley lines to Canadian isolates of the pathogen. A nursery in Njoro, Kenya, is providing field screening for stem rust (Ug99 races) and stripe rust races for programs evaluating rust diseases in cereals, and by using winter nurseries in New Zealand, researchers are able to select for fusarium resistance and leaf and stripe rust resistance while advancing generations. Chibbar’s team in Saskatchewan will use northern European and/or Russian wheat lines to seek out new sources of cold tolerance that could be bred into Canadian winter wheat cultivars. And a cooperative research plan between China and Canada for blackleg risk mitigation is collating and sharing data and results from research projects in the two countries.
Private companies are also increasingly involved in global collaborations. For example, Monsanto currently collaborates with Australian and European researchers on canola disease studies such as those on blackleg. “We have a sister breeding group in Europe and it’s a tremendous opportunity to share information and germplasm back and forth to utilize the best tools that we can,” says Anderson.
On the Horizon
The Western Grains Research Foundation recently announced $3.5 million of new funding for 25 crop-related research projects through a co-funding partnership with the Agriculture Development Fund and producer commodity groups. The WGRF’s endowment fund supports research on a broad range of crops and has a number of key priority areas, including crop risk management.
Projects receiving funding include mapping of blackleg in canola, fusarium resistance in cereals, new technologies to assess sprouting damage in wheat, building durable clubroot resistance in canola, pulse disease management and improving weed management for growers.
Canola
The clubroot resistant varieties available to producers remain the only truly effective control against the disease. Canola varieties with stacked resistance are likely to be available soon.
The leading research on developing new sources of clubroot resistance was funded by the Clubroot Risk Mitigation Initiative through Growing Forward 1. Genyi Li at the University of Manitoba, Habbibur Rahman at the University of Alberta and AAFC’s Saskatoon Research Centre have identified and developed new sources of clubroot resistance, which should soon be available for breeders.
Resistance to blackleg is already weakening under certain conditions, and new races of the pathogen that have potentially adapted to resistant canola cultivars are cause for concern. Researchers are trying to develop a strategy to mitigate the impact of pathogen population change; for example, Dilantha Fernando from the University of Manitoba and Gary Peng from AAFC’s Saskatoon Research Centre are monitoring blackleg pathogen races present on the Prairies. The researchers are analyzing the resistance genes available in commercial varieties in order to make recommendations to growers about how to rotate different resistant varieties more effectively. The research is supported by the Canola Agronomic Research Program, which receives funds from canola growers’ associations in Alberta, Manitoba and Saskatchewan as well as the Canola Council of Canada.
There are few genetic sources of true sclerotinia resistance available to plant breeders, making the development of sclerotinia tolerant varieties challenging. Projects include work led by Lone Buchwaldt at AAFC. She is collaborating with colleagues at the Saskatoon Research Centre on mapping the quantitative resistance loci in Brassica napus germplasm from Asia and Europe. They are also examining the contribution of individual defense genes in more detail. Preliminary data on the pathogen itself has revealed it is genetically diverse across the three Prairie provinces and isolates vary in the level of aggressiveness on canola.
Cereals
Rusts remain a major focus of cereal research programs. Many studies are large in scope, involving researchers from across Canada as well as internationally, as is the case with Ug99 research.
Stephen Fox, a wheat breeder at Winnipeg’s AAFC Cereal Research Centre, is screening material for resistance to stem, leaf and stripe rust resistance, and is close to registration of a new variety that may offer some resistance to the Ug99 group of stem rust races. Curtis Pozniak at the Crop Development Centre at the University of Saskatchewan is also involved in rust resistance research, and is completing an inventory of advanced genetic plant material from work initiated by the late Douglas Knott, which will be made widely available to breeders and pathologists.
In the case of leaf rust, varieties have relied heavily on a single gene, Lr21, for many years—to the point where it has become highly leveraged in many areas of the United States and Canada. Canadian researchers are adding other genes to diversify the basis of leaf rust resistance in spring wheat.
Fox’s team is also characterizing resistance genes in Fusarium, which will hopefully lead to the development of better molecular markers to more easily identify and retain sources of resistance.
Soybeans and Corn
Although soybeans and corn are relatively new crops to Western Canada, there is growing interest among producers in varieties that can perform well in shorter growing seasons. As a result, retail seed companies are selecting new corn varieties that offer early silking and early pollination. In addition, at least two of the major trait development companies plan to roll out new soybean varieties—touted to be better suited to Manitoba growing conditions as well as other newer soybean-growing areas—over the next two years.
Angela Lovell
