UCR biologist receives $1.75 million grant to study plant-threatenin...( ic pattern as to which species each typ...)

According to Nunney, new Xylella strains are evolving, thus complicating the research being done on the bacterium. We started to pick up some strains that showed a mixture of all three North American subspecies. They may have picked up pieces of DNA from dead bacteria. We think this interchange of genetic material is relatively recentprobably during the last 100 years or so.

Each of the new strains of Xylella identified so far attacks different plants than do the original Xylella subspecies Thats worrisome, Nunney said. Clearly, we need to know more about the genetic basis of host specificity.

In the next four years, Nunney and his research group will develop a nationwide map of different subspecies of Xylella, and an effective monitoring system both to catch foreign forms introduced into the United States and new forms evolving within the country. With its South American partners, Nunneys group will explore the geographical origins of the different forms of Xylella.

Are there yet more unknown forms of Xylella in the native plants of Central and South America" Nunney asked. Citrus is not native to South America, so Xylella must have been living in something else before citrus was introduced, since that form is older than the citrus introduction on that continent. We have to understand the interrelationship with all forms before we can understand the current and future dangers posed by Xylella to grapevines and to other plants as well.