Scientists believe Asian soybean rust reached the continental U.S. in one of two ways.
1. Wind
2. Over the land bridge between North America and South America.
Additional images and information can be viewed on the Iowa State Asian Soybean Rust site.
HISTORY
Soybean rust was first
identified in Japan in 1902, and has since spread throughout Asia and
Australia. The South American native rust was mistaken as Asian soybean
rust when it was discovered in Puerto Rico (1974) and South America in
(1979).
The second phase of
this global movement began with the discovery of the fungus in Africa
in the 1990s. In 2001, Asian soybean rust was identified in South America
and has since become established and spread throughout the region, infecting
an area 1,500 miles long from near the Equator and southward.
Soybean rust is also
found in Hawaii (P. pachyrhizi), which along with Puerto Rico (P.
meibomiae) is an area where a large amount of U.S. soybean seedstock
breeding occurs. The logistics involved with seedstock production and
transport had been a concern of moving the pathogen to the mainland U.S.
Researchers theorize
that soybean rust spores are able to easily move long distances on wind
currents. In a matter of only six years, Asian soybean rust was able to disperse
itself across much of Africa, and it took only three years to spread across
most of South America as well.
Spread of the rust
may have occurred in many ways; inoculum is speculated to have moved to
Hawaii with plant materials, and mass air movement was the suspected cause of
movement from Asia to Africa to South America. Inoculum may also be accidentally transported by travellers, or may be intentially moved as an act of bio-terrorism.
As theorized, the rust moved north from South America into the southern United States, sooner than once predicted, thanks to the strong hurricane season of fall 2004.
(information courtesy
ISU and the Crop Adviser Institute)
Additional interactive resource on the Web: University of Missouri-Columbia Extension Soybean Rust Guide
