Progress With Rust-Resistant Confections
As many confection sunflower growers know all too well, the level of rust resistance in confection hybrids has lagged below that available in oil-type hybrids. Widely effective sources of resistance to sunflower rust have proven elusive through the years, requiring confection producers to rely on fungicide treatments for management of this disease.
There’s good news on the horizon, however. Research being conducted at the USDA-ARS Sunflower and Plant Biology Research Unit at Fargo, N.D., should result in the release — sometime in 2013 — of confection lines that carry good resistance to sunflower rust. The research project has been partially funded by the National Sunflower Association and the Specialty Crop Block Grant Program administered by the North Dakota Department of Agriculture.
“The goal of the project has been to incorporate rust-resistant genes into an acceptable genetic background — and to then make them available to the private seed industry to create commercial resistant hybrids,” notes Lili Qi, research molecular geneticist with the Fargo unit and the project’s leader. She expects three rust-resistant confection lines — possessing the resistance genes R2, R4 and R5, respectively — to be released to commercial breeders later this year.
These resistance lines were developed using the backcross method, Qi says. The three resistance genes came from three oil sunflower lines. The oil lines were selected as “donor” parents, while two confection lines were selected as “recurrent” parents. “Crossing the recurrent parent with the donor parent produced an F1 hybrid; then, crossing the F1 with the recurrent parent produced the first backcross generation (BC1),” the USDA geneticist explains.
After screening the cross for rust resistance, Qi’s team developed several subsequent backcross generations by repeatedly crossing the selected BC plants with the recurrent parent. In total, “seven generations of back crosses with plant material containing a resistant gene are required for the final product,” she says. “After the final backcross generation, selected individuals were self-pollinated so that the selected lines are homozygous for the rust resistance.” The USDA group confirmed the stability of the rust-resistant genes by using genetic DNA markers and a rust test.
Of course, the final product also must possess strong agronomics. Qi reports that field tests actually showed agronomic improvement in terms of plant vigor, plant height, seed size and seed color. In the end, these three new lines are very similar to the confection recurrent parent — with the notable difference being that they, unlike the parent, possess rust resistance.
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