A Better Understanding of a Major Threat to
Wheat By Dennis
O'Brien May 5, 2009
The pathogen that causes the world's most common wheat disease is a
moving target, but scientists are now better equipped to keep track of it,
thanks to some genetic sleuthing by Agricultural Research Service (ARS)
Up to 60 resistance genes have been known to combat Puccinia
triticina, the fungus that causes wheat leaf rust. But the pathogen is so
genetically diverse and quick to adapt that most wheat resistance genes prove
ineffective within a few years.
The stakes are high. Leaf rust is the world's most widely distributed
wheat disease, and in Kansas alone wheat producers lost 14 percent of their
crop--some 50 million bushels--to a leaf rust epidemic in 2007. Emerging
strains of P. triticina are an increasing threat to soft red winter
wheat in the southeastern United States, and to hard red winter wheat and hard
red spring wheat in the Great Plains, according to
Kolmer, a plant pathologist at the ARS
Disease Laboratory in St. Paul, Minn.
Kolmer recently completed a comprehensive genetic analysis of emerging
strains of P. triticina collected in a recent survey of North America's
major wheat-producing areas, probing the strains with DNA markers specifically
developed for the leaf rust fungus and for virulence capable of overcoming
wheat leaf rust resistance genes.
Kolmer found that the strains of P. triticina infecting wheat
in North America fall into five genetically distinct groups, with two widely
distributed groups accounting for 90 percent of the total population. The five
groups also differ in their ability to overcome a number of resistance genes,
an indication that different groups of P. triticina develop virulence
traits at different rates.
The work, to be published in the journal Phytopathology, will
help researchers identify the origins of emerging strains of P.
triticina, unravel clues about migration patterns, monitor shifts in
virulence and figure out why some resistance genes are more effective and
long-lasting than others.
ARS is the principal intramural scientific research agency of the
U.S. Department of