Bacterial wilt causes nightmares for cucurbit growers in the Midwest and East. Plants wilt and die from the bacterium (Erwinia tracheiphila), which spreads though a field courtesy of cucumber beetles. Muskmelon and cucumber growers are way too familiar with bacterial wilt, but it attacks squash crops too. The sad fact is that scientists know very little about the bacterium, so our bag of tricks against bacterial wilt consists mostly of insecticide applications. Our current four-state (Iowa, Ohio, Kentucky, and Pennsylvania) USDA-SCRI project is looking more closely at E. tracheiphila to uncover some of its secrets. One interesting nugget we’ve unearthed is that there are actually two distinct wilt bacteria; the type that attacks melons and cucumbers is different from the type that attacks squash.  Nobody realized that before. That’s a useful clue, because it helps us to penetrate the genetic code of E. tracheiphila to find the genes that make plant-host preference happen. This process is like prying the lid off a can of worms; once you get in there, you can find all sorts of interesting things. Thanks to Iowa State bacteriologist Gwyn Beattie, we have also found genes that may help to infect plants. This is real progress against bacterial wilt. Once we know how it operates, we can figure out how to defeat it more efficiently and with less need for insecticides.

Mark Gleason, Iowa State University