When farmers packed a meeting hall in Swift Current, Saskatchewan, for the 2018 Durum Summit, they were hoping to find a solution to their fusarium problems. Unfortunately, there’s nothing new on the horizon for the next few years.
Curtis Pozniak, a wheat breeder and geneticist at the Crop Development Centre in Saskatoon, says they are seeing developments in fusarium resistance in new durum varieties. “It’s slow, but there’s an improvement,” he told the audience.
Weather conditions in 2017 were not conducive to too much fusarium infection in most of the durum-growing regions, but farmers are still reeling from extensive damage in 2016. Breeders are doing all they can. But when Pozniak was asked, “Which two traits have been most difficult to breed for?” Pozniak’s answer was “fusarium and fusarium.”
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Some factors make it difficult for breeders to develop fusarium-resistant durum.
Little native resistance: First, Pozniak said, “there’s not a lot of native resistance.” When they are looking for genes that might contribute to resistance, they don’t have a lot of options. “We don’t have a lot of genes in the native durum germplasm pool that we can use.”
So many genes: In the case of wheat midge tolerant spring wheat, a single gene makes the plants resistant to the pest. But no single gene does the job with fusarium. Instead, breeders “stack” genes — ensuring genes that might contribute to resistance are included in a potential new variety.
Ron Knox is a plant biotechnology research scientist with Agriculture and Agri-Food Canada at Swift Current. He explained the complexity of the situation. “In bread wheats there’s over 200 genes, so far, that people have identified. It’s a very complex disease, genetically.”
With several genes contributing to fusarium tolerance, it can be difficult to measure the contribution made by each individual gene.
The sheer variation: Fusarium infection is so dependent on weather that evaluation “requires testing over multiple environments, testing the same material multiple times. And we have large year-to-year variation in this disease.”
This variation takes place not just in the field, but even in researchers’ specialized FHB nurseries. “There’s still a lot of nursery-to-nursery variation,” Knox said.
The trouble with DON: While it’s easy to identify fusarium damage, it’s not simple to test for DON, the mycotoxin deoxynivalenol, or vomitoxin. Measuring DON requires sophisticated, expensive tests.
Only a few years ago, Pozniak said, researchers didn’t have the capacity to select for DON susceptibility early in the breeding process. Instead varieties showing some promise would be further along in the breeding process before they were screened out due to susceptibility to DON. “We were only screening, we weren’t actually selecting.”
As Knox said, “We put a lot of emphasis on DON, but we haven’t had the resources to do selection directly for DON.”
As well as the cost of the tests, Knox pointed out, testing for DON requires additional labour during the harvest, and threshing of material.
Not all bad news
While fusarium has been top of mind, it wasn’t the only topic on the agenda.
“We’ve identified a couple of interesting dwarfing genes,” Pozniak told farmers. His team is breeding dwarfing genes from Australia into the Canadian germplasm. “When we add the dwarfing gene in we’re reducing the plant height by about 30 per cent.”
Breeders are also working on sprouting tolerance. They’re bringing genes for this in from bread wheat, “reducing the amount of sprouted kernels by about 80 per cent,” Pozniak said. These new varieties “are starting to move into the advanced stages of yield tests.”
Ken McDougall from McDougall Acres, a seed farm near Moose Jaw, Sask., was part of a producer panel that closed the Summit. McDougall pointed to the genetic advances we’ve already seen in durum seed. “Five years ago we had four options,” he said. These days, there are several potential durum varieties that he could promote to his customers. “That makes it much more complicated for seed growers,” he joked. “The new varieties that we have access to are quite exciting.”
Farmer Kris Ewen, a farmer and durum grower from Riverhurst, Sask., summed it up when he said he would keep growing durum, even without a fusarium-tolerant variety in the near future. “We’re in a durum-growing area. I don’t think it’s a crop we can let go.”
Rating for fusarium
After they check out the “yield” column for each new variety, most farmers reading the annual seed guide look to see how each variety might stand up against the most worrying diseases.
Curtis Pozniak, durum breeder at the Crop Development Centre, explained that when breeders rate durum seed varieties for fusarium resistance (ranging from R, resist- ant, to S, susceptible), they take three actors into account.
- Incidence: 20 per cent of the weighting. Incidence describes the number out of out 100 heads of durum in a field showing symptoms of infection.
- Severity: 20 per cent of the weighting. Severity describes how badly the head of the plant has been damaged by fusarium.
- DON: 60 per cent of the weighting. This factor measures the presence of deoxynivalenol (DON), also known as vomitoxin. DON is produced by fusarium graminearum. Because it can be toxic, DON is given a high weighting.
The Government of Saskatchewan’s “Varieties of grain crops, 2018” has this to say: “Although no varieties are resistant, Brigade, CDC Credence and Transcend generally express lower FHB symptoms compared to other cultivars in the class. Mycotoxin (DON) production by FHB fungi is generally lower for Transcend.”
Pozniak explained: “Brigade and CDC Credence have an MS [moderately susceptible] rating more because they have reduced severity in the disease.”
