Sunflower Stalk Rot

Sunflower Fungi Research

Improved disease resistance could be in store for tomorrow's sunflower varieties, thanks to plants that scientists have collected in Australia and are evaluating in greenhouse trials in Fargo, North Dakota.   Plant pathologists and botanists collected seeds of wild sunflowers while in Australia in spring 2007.   An arm of the Australian government, the Plant Exploration Office, funded their trip. Assisted by their Australian hosts, the plant specialists traveled to every corner of Australia to make 59 collections of Helianthus annuus and H. debilis sunflowers, marking the first time researchers have collected these wild species outside the plants' native United States.

The ultimate goal is to find new genes that can be incorporated into American sunflower hybrids to make them more resistant to fungi that cause diseases such as downy mildew, rust, and Sclerotinia stalk rot. Each year, outbreaks of stalk rot and other forms of Sclerotinia disease cost about $252 million annually in losses to U.S. sunflower, canola, soybean, and other susceptible crops.

In Australia, however, rust is the bigger menace. There, mild to subtropical climates in areas where sunflowers grow allow the rust fungus, Puccinia helianthi, to skip its winter survival phase and evolve more rapidly via sexual recombination. The result is a far greater diversity of rust races in Australia than those observed in the United States. The plant specialists’ hope is that rust's nearly year-round presence has prompted a kind of sunflower survival of the fittest, whereby genes from the hardiest Aussie plants could be used to fortify the defenses of their U.S. brethren.

In fall 2007, the scientists began greenhouse trials of the 59 wild Australian sunflower populations they had collected to evaluate their resistance to downy mildew, which doesn't currently exist in Australia, and to rust, which is severe there.   The sunflower varieties collected in Australia will also be...