Rapid global spread of two aggressive strains of a wheat rust fungus

Abstract

Rust fungi can overcome the effect of host resistance genes rapidly, and spores can disperse
long distance by wind. Here we demonstrate a foreign incursion of similar strains of the
wheat yellow rust fungus, Puccinia striiformis f. sp. tritici, in North America, Australia and
Europe in less than 3 years. One strain defined by identity at 15 virulence loci and 130
amplified fragment length polymorphism (AFLP) fragments was exclusive to North America
(present since 2000) and Australia (since 2002). Another strain of the same virulence phenotype,
but differing in two AFLP fragments, was exclusive to Europe (present since 2000–2001) as
well as Western and Central Asia and the Red Sea Area (first appearance unknown). This
may be the most rapid spread of an important crop pathogen on the global scale. The limited
divergence between the two strains and their derivatives, and the temporal–spatial occurrence
pattern confirmed a recent spread. The data gave evidence for additional intercontinental
dispersal events in the past, that is, many isolates sampled before 2000 in Europe,
North America and Australia had similar AFLP fingerprints, and isolates from South
Africa, which showed no divergence in AFLP, differed by only two fragments from particular
isolates from Central Asia, West Asia and South Europe, respectively. Previous research
has demonstrated that isolates of the two new strains produced up to two to three
times more spores per day than strains found in USA and Europe before 2000, suggesting that increased aggressiveness at this level may accelerate global spread of crop
pathogens