Acetolactate synthase (ALS)-inhibiting herbicides have been widely used to control the weed hairy beggarticks (Bidens pilosa). The selection pressure caused by intensive herbicide use has selected hairy beggarticks resistant biotypes. The objectives of this work were to evaluate the degree of genetic similarity among hairy beggarticks accesses (Bidens pilosa) resistant to ALS-inhibiting herbicides, and to evaluate the relation between genetic similarity and geographic distance. Seeds of two groups of hairy beggarticks accesses resistant to ALS-inhibitors were sampled from a farm at Pato Branco, Paraná, and seedlings were grown in the greenhouse at the Universidade Federal do Rio Grande do Sul (UFRGS), Porto Alegre, RS, in Ocober/2004. The use of RAPD (Random Amplified Polymorphic DNA) molecular markers allowed evaluating the genetic similarity among hairy beggarticks accesses. In the analysis of both access groups, out of twenty primers assessed, only seventeen displayed polymorphism and amplified a total of 94 bands. There is low genetic similarity (38%) among hairy beggarticks accesses resistant to ALS inhibitors from the same farm. There is no relationship between genetic distance and geographic distance in the evaluated accesses.
resistance; hairy beggarticks; genetic variability
