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USDA Develops More Downy Mildew Resistant Lines

Saturday, September 15, 2007
filed under: Research and Development

The USDA Sunflower Research Unit in Fargo and the North Dakota Agricultural Experiment Station have jointly developed, tested and released three new high oleic sunflower lines with genetic resistance to downy mildew.

In repeated field and greenhouse tests at Fargo, all three new lines – dubbed HA 458, HA 459 and HA 460 – resisted the most virulent races of downy mildew fungus found in North America. HA 458 and HA 460 also withstood a French race not yet found in America. Oil extracted from HA 458 and HA 459 averaged 86.5% and 87.3% oleic acid, respectively. Oil from HA 460 had 88.8% oleic acid.

USDA plant pathologist Tom Gulya assisted geneticist Jerry Miller, now retired, in developing the new high oleic germplasm by crossing elite sunflower lines with wild sunflowers collected from Idaho and Texas by USDA botanist Gerald Seiler. Jack Rasmussen of the NDAES collaborated with them.

Excessively wet and cool spring growing conditions was ideal for downy mildew development in some parts of the Northern Plains this year. With downy mildew, like most crop diseases, three conditions must be met for a disease outbreak to occur: 1) the presence of a susceptible crop host; 2) a pathogen strain or strains specific to the crop host; and 3) the right environment for infection to proliferate. If there is enough soil moisture for seeds to germinate, but not excessive rain, seedlings will escape infection even if the DM fungus is present.

Fortunately, more sunflower hybrids are being developed with resistance to all known races of the disease – a number of DM resistant NuSun hybrids are already commercially available. Some seed companies have also introduced a DM resistant Clearfield NuSun, a DM resistant confection, and a DM resistant high oleic hybrid. The significance of these newest HO lines released by USDA is that they combine DM resistance with the high oleic characteristic in one germplasm package, making it easier for commercial breeders to use it for breeding commercial hybrids.

See the list of DM resistant hybrids and other new hybrids released by all the major seed companies for the 2007 growing season online at – click on ‘Sunflower magazine,’ then ‘view archives.’ Under ‘Hybrid Selection/Planting’ see the article ‘Sunflower Hybrids for 2007.’

North Dakota State University tracked DM incidence – percentage of plants infected with downy mildew – in its summer IPM survey. Go to - there, click on ‘Sunflower.’ Updated maps indicating DM incidence in N.D. counties are given, as well as surveys for sunflower beetle (larvae and adult) and the banded sunflower moth.

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