http://www.ars.usda.gov/is/pr/2005/051101.htm
November 1, 2005
Hydrilla's Resistance to Herbicide Gives
Scientists a New Challenge
By Luis Pons
Scientists with the Agricultural Research Service (ARS) and a
private firm have encountered a troubling turn of events in the
fight against an invasive weed that's choking many waterways in
the southeastern United States.
The researchers--at ARS' Natural Products Utilization Research
Unit in Oxford, Miss., and with SePRO Corp., a Carmel, Ind.-based
plant-protection management firm--found
that a form of hydrilla (Hydrilla verticillata) has developed
resistance to fluridone, the most effective herbicide against
it.
They've pegged the resistance to a gene mutation in the dioecious,
female form of hydrilla. So far, this mutation has been found
only in hydrilla inhabiting several Florida lakes. A monoecious
hydrilla--a form that has both male and female flowers on the
same plant--that first appeared in the middle Atlantic states
has, to date, not shown resistance to the herbicide.
The ARS studies in Oxford were conducted by plant physiologist
Franck Dayan and molecular biologists Brian Scheffler and Albrecht
Michel. Scheffler now leads ARS' Mid-South Area Genomics Laboratory
in Stoneville, Miss., while Michel is no longer with ARS.
Hydrilla's ability to thrive even in adverse conditions has led
researchers to dub it "the perfect aquatic weed." Rooted
in bottom sediments, it grows long, thin stems that rapidly reach
the water's surface and form a thick mat. It was introduced to
the United States from Southeast Asia in the 1950s near Tampa,
Fla.
According to Dayan, the resistant hydrilla has increased treatment
costs for affected lakes.
The new discoveries have spurred government and SePRO scientists
and aquatic systems managers to seek additional environmentally
friendly ways to combat the weed. Biological agents being studied
for controlling hydrilla include some insects and the fungal pathogen
Mycoleptodiscus terrestris, which when used with fluridone seems
to increase hydrilla's susceptibility to the herbicide.
Read more about this research in the
November 2005 issue of Agricultural Research magazine.
ARS is the U.S. Department of Agriculture's chief in-house scientific
research agency.