Plant breeders are searching for new barley varieties that can fight off scald and stripe rust.
Scald is the primary fungus that hits barley, limiting production for growers in central Alberta, said plant pathologist Kequan Xi of Alberta Agriculture’s Field Crop Development Centre in Lacombe.
Varieties that once showed resistance are breaking down as scald mutates and becomes more virulent, he said at the Canadian barley symposium.
Over time, varieties such as Harrington and CDC Guardian have become more susceptible to scald and the problem is now showing up in popular malt barleys such as AC Metcalfe and Lacombe.
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Barley varieties that descended from Harrington appeared to have more disease trouble.
“These varieties may not hold resistance under high disease pressure,” he said.
There were widespread problems with scald in 2011, and re-searchers are using genetic tools to develop new varieties to withstand the disease.
They have found that Manny and Earl have greater disease resistance under severe epidemic years but are not sure why at this point.
Stripe rust, another serious disease, is occurring in Western Canada after travelling north from South America, Texas and the Pacific Northwest, said Joseph Nyachiro of the crop development centre.
Stripe rust has been found in wheat in Alberta, Manitoba and Saskatchewan. It has also been found in barley and appears to be a different strain than the one that strikes wheat.
Alberta started seeing severe rust in 2002, and the disease has in-creased in severity and moved into areas where it was not previously detected.
“There is no doubt that stripe rust is becoming a major disease,” he said.
It has been seen as far north as Barrhead, north of Edmonton.
“In the course of time, the disease will go even farther north,” he said.
Stripe rust has been seen at nearly all the centre’s research sites since 2003 and significantly affects crop performance.
“Here in Canada, we don’t have really good information on how much yield loss it can cause,” he said.
This form of stripe rust also appears to be more virulent, which Xi said may be due to hybridization.
It can go through four to six breeding cycles in a season, so it evolves quickly.
“With that rapid disease cycle, this pathogen, especially stripe rust, has a chance to evolve into new pathotypes that can infect a plant,” he said.
Barley varieties derived from Vivar, Trochu, Sundre and Seebe have variable levels of resistance. Two-row barley varieties appear to be more resistant than six-row types.
Nyachiro said characterizing the resistant genes is a challenge.
“We need to target for durable resistant genes to circumvent this problem,” he said.
Researchers do not know if single or multiple genes confer stripe rust resistance. Breeders have made progress in developing resistant varieties in the United States, but they are not grown in Canada.
Alberta conditions have allowed this disease to spread recently during cool, wet summers.
The fungus overwinters on volunteers and weeds. Spores can germinate in temperatures from zero to 20 C. Its optimum temperature is 7 to 12 C.
Researchers have also found it can go into dormancy until favourable conditions return, but it will not usually survive at – 10 C or lower.
However, a study on overwintering showed it can survive a Canadian winter and reinfect plants at early growth stages.
