US scientists have developed three new sunflower hybrids that are resistant to downy mildew and produce oil rich in oleic fatty acid.

Downy mildew fungus causes white cottony growth in young sunflowers, and large, clublike roots and stunted growth in older ones.

Until recently, sunflowers growers used seeds that had been treated with the fungicide metalaxyl, which the fungus has since become resistant to. The emergence of virulent new strains of downy mildew - from just two before 2003 to 15 now - has spurred the need for hybrids with new sources of disease resistance.

In tests, all three new lines resisted downy mildew fungus, with two also withstanding a French race not yet found in the US.