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A solid step in durum breeding

A new durum variety raises the bar for Prairie farmers and makes life a lot more challenging for one of their common nemeses — sawflies. AAC Raymore, released by SeCan to all its member seed growers in February 2013, is an amber durum (CWAD) with similar yield, quality and agronomic traits to AC Strongfield, but with the added bonus of a solid stem, which makes it a far less hospitable host to sawfly than traditional hollow-stem varieties.

AAC Raymore

AAC Raymore was developed by Agriculture and Agri-Food Canada’s Danny Singh, along with fellow plant breeders who have been working on improving durum yield and agronomics for many years at the Swift Current, Sask., research station. Other solid-stem varieties have been developed in the past, but they either did not meet the quality specifications for CWAD or had agronomic weaknesses like poor straw strength.

“In addition to protection against wheat stem sawfly, AAC Raymore has a competitive overall package for grain yield, protein and quality acceptable for CWAD,” says Singh “It is a large seeded cultivar and has good resistance to the majority of diseases, including stripe rust and common root rot.”

Solid-stem varieties of wheat like AC Lillian have been available for several years, gaining popularity due to their sawfly tolerance, but AAC Raymore is the first solid-stem variety of CWAD to be registered in Canada. According to Scott Meers, insect management specialist with Alberta Agriculture and Rural Development, the solid stem reduces the sawfly population in two ways.

“The solidness in the stem increases the mortality of the sawfly larvae and the sawfly that do manage to get through and cut the wheat actually lay fewer eggs the next year,” says Meers. A study quoted by Saskatchewan Agriculture in 2006 found larval mortality to be 28 per cent in hollow stems and about 67 per cent in solid stems.

Sawflies and stems

Sawflies, which are not true flies but actually relatives of bees, wasps and ants, typically favour the hot, dry climate that is characteristic of traditional durum- growing areas, although they have been found in other areas of the Prairies as well. Female sawflies cut into stems of wheat and durum with a saw-like organ and lay their eggs there in June and July.

When the larvae hatch they move through the stem, eventually cutting a groove around the edge of the stem near ground level. Wind or rain can knock over the weakened stem, making it difficult to pick the heads off the ground at harvest time.

Sawfly larvae also contribute to yield loss. They feed on the nutrient-carrying phloem tissue inside the stem, leading to fewer or more shrivelled seeds per head.

“In a hollow variety [the larvae] can get to the cells inside the stem that are very easy for the young sawfly to eat,” says Meers. “In the solid stem the eggs are laid right inside the stem and the young sawfly can’t get outside of the solid tissue.”

Sawfly resistance

Jim Downey, SeCan’s research and development manager, is optimistic about the potential of this new variety to resist sawfly.

“Raymore has an exceptionally solid stem. It expresses the pith to fill the stem from the ground to the head,” said Downey. In contrast, he said that the Hard Red Spring wheat solid stem trait is not expressed as well. Cloudy or rainy weather at time of stem elongation can lead to less solid stems.

Barry Reisner is a pedigreed seed grower near Limerick in southwest Saskatchewan. He splits his cereal acres between CWRS wheat and durum, including a seven-acre plot of AAC Raymore in 2012.

“The vast majority of the stems were solid — not just partially solid but totally solid,” says Reisner of his 2012 crop. In his experience growing solid-stem wheat, it is unusual to have more than 50 per cent solid stems, which means it takes longer to control the sawfly population.

“That’s why we’re interested in Raymore — because it could be more of an immediate cure for sawfly,” says Reisner. “I don’t know for sure, but I expect it will be.”

Growing AAC Raymore

Reisner and other SeCan members will be producing higher generation seed in the 2013 and 2014 seasons with certified seed available for commercial growers in spring 2015. While the sawfly population is at a low point in the cycle following highs between 2001 and 2007, there is still a strong argument to be made for growing AAC Raymore now.

“To me it looks like you could potentially grow Raymore as your main durum variety without any downside,” says Downey. Along with resistance to sawfly, AAC Raymore also boasted the highest protein of the durum varieties grown in the co-operative tests between 2008 and 2011.

“We never really know until it gets out on farmers’ fields what the grade retention will be, and that’s a big deal in durum,” says Downey. “One of the things we really don’t know is how it will hold colour. Starchy kernels are kind of white. The hard vitreous colour that’s desirable should be achievable because of the high protein.”

There is more durum research to be done. Downey describes the “holy grail” as a variety that combines a solid stem with midge tolerance and fusarium resistance. (AAC Raymore saw no improvement over the checks in fusarium head blight susceptibility.) Multiple resistances in one variety requires parent varieties that carry the different resistant genetics as agronomic and quality traits.

“More crosses will be made in the future based off the platform of Raymore,” Downey sauys. “Solid-stem may not become required trait for registration but it will be available for future varieties.”

In Downey’s view, AAC Raymore demonstrates the importance of Canada’s public plant breeders. “Ag Canada has said they want to get out of wheat finishing programs but the Swift Current site is a national treasure because of all the good work that has gone into developing good parents.” †

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Sarah Weigum

Sarah Weigum grows pedigreed seed and writes at Three Hills, Alta.

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