INHERITANCE OF RESISTANCE TO PROTOPORPHYRINOGEN OXIDASE INHIBITOR HERBICIDES IN WILD POINSETTIA

ABSTRACT Weed resistance to herbicides is a major global problem for agriculture. In recent years, the increased use of herbicides, without proper planning, has led to a large increase in the number of cases of weed biotypes that are resistant to one or more herbicide mechanism of action. Wild poinsettia biotypes (Euphorbia heterophylla), discovered in the State of Paraná, with resistance to herbicides that inhibit protoporphyrinogen oxidase (PROTOX) and acetolactate synthase (ALS), are the first case to exhibit multiple resistance in Brazil. This study analyzed the genetic inheritance of PROTOX inhibiting herbicide resistance in E. heterophylla. Crosses were conducted between biotypes that were susceptible (female parent) and those carrying multiple resistance to ALS and PROTOX inhibitors (male parent) to obtain the F1 generation. Backcrosses were performed (RC1 and RC2) and the F1 generation was advanced to F2. F1, F2, RC1, RC2 generation plants and their parents were subjected to applications of the herbicide fomesafen (250 g i.a. ha-1). The observed frequencies in the F2 generation were not different from the expected frequency of 3:1. All RC2 individuals were resistant, while the RC1 population showed a 1:1 segregation, which would be expected when a single gene controls the trait. Thus, it can be inferred that E. heterophylla resistance to PROTOX-inhibiting herbicides is conditioned by a single and dominant nuclear gene.