Genetic variation in the pds gene and its relation to fluridone resistance in Hydrilla verticillata

Abstract

Hydrilla verticillata is an invasive aquatic weed in the United States that has recently developed resistance to the herbicide fluridone due to point mutations in the pds gene. I amplified and sequenced the pds gene of 49 hydrilla samples from five Florida water bodies that vary in resistance to fluridone from none to very high. Genetic diversity within individuals was high with most individuals having 2-3 different pds alleles. I found two previously described resistance alleles and their occurrence across water bodies was broadly consistent with the observed levels of fluridone resistance. Fluridone resistance alleles were also cloned at higher frequencies within individuals than the susceptible alleles in water bodies with intermediate and high resistance to fluridone suggesting there are multiple copies of these alleles. Our study suggests that point mutations and allele copy number may both be responsible for fluridone resistance in hydrilla