Tuesday, September 26, 2006

Kudzu, Hurricanes and Soybean Rust

I may be a fungus freak, but learning life cycles is, well, a necessary evil. Rusts, plant pathogens with up to five types of spores, are a particular pain. So today's lecture on rusts in my mycology class was a bit less than exciting -- that is, until we got to soybean rust. The organism is not particularly fascinating, but the story of how it got to the United States is worth telling.

Like soybeans, soybean rust is native to East Asia. As soybean cultivation spread worldwide, so did the rust. In the 1950s and 1960s, it spread through South Asia and Australia. In 1994, it reached Hawaii, but the continental US was protected by long distances and careful inspection of imported plants.

The beginning of the end of this isolation came in 1997, when a cyclone carried the fungus from India to central Africa. In a few years, it reached both South Africa and the Atlantic coast. Then, transported by either wind or airplanes, the rust showed up in Paraguay in 2002. From Paraguay, the fungus' highly mobile spores dispersed to Venezuela and Brazil. After that, it was only a matter of time before soybean rust showed up in the continental US.

It didn't take long. In September 2004, Hurricane Ivan blew spores from South America to the American South, introducing the rust to Louisiana, Mississippi, Georgia and Florida. Farmers are now trying to control the pathogen, which attacks a wide range of legumes. So far, damage has not been serious.

So what's up with kudzu? It turns out that this vine, a Japanese import ubiquitous in the South, is one of the hosts of soybean rust. This means it can become a reservoir for the disease -- unfortunately, without sustaining much damage itself. You gotta love ecology!

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