Researchers at the U.S. Department of Agriculture's Agricultural Research Service say they found it's because the fungus that causes the wheat disease called stripe rust can use sexual recombination to adapt to resistant varieties of wheat.
Plant pathologist Yue Jin and colleagues Les Szabo and Marty Carson said they've shown for the first time that stripe rust, caused by Puccinia striiformis, is capable of sexually reproducing on the leaves of an alternate host called barberry, a common ornamental. The fungus also goes through asexual mutation. But sexual recombination offers an advantage because it promotes rapid reshuffling of virulence gene combinations and produces a genetic mix more likely to pass along traits that improve the chances for survival.
Barberry (Berberis spp) is already controlled in areas where wheat is threatened by stem rust, caused by another fungal pathogen. But the ARS team said its findings are expected to lead to better control of barberry in areas like the Pacific Northwest, where lower temperatures during most of the wheat growing season make stripe rust a particular threat.
The results of the study recently appeared in the journal Phytopathology.