The objective of this study was to assess efficacy of the glyphosate in three populations of Conyza canadensis, two suspected of resistance (B15-1 and B15-2) and a susceptible one (B), from intensive olive orchards in Alentejo, south of Portugal. There were performed: seedling-Petri plate assays, greenhouse dose-response assays and a shikimate accumulation assay. The seedling-petri plate assays showed that B population had significant higher germination (60-80%) than B15-1 (31.3%) and B15-2 (52.7%) populations. There was evidence of resistance in the B15-1 population and susceptibility of the B15-2 population. Mortality was the key parameter to distinguish between populations by the discriminating concentration: 0.3 mM glyphosate. The dose-response assays revealed a resistance level of 0.52 and ED50 of 59.2 g e.a. ha-1 (Bioassay I) and 87.2 g e.a. ha-1 (Bioassay II) for B15-2 population. The B population showed an ED50 of 113.3 g e.a. ha-1. The shikimate accumulation assay indicated susceptibility of both populations (B and B15-2), although the accumulation was higher in the B population (0.69 μg mg-1) than in the B15-2 population (0.49 μg mg-1), six days after application (720 g ha-1). The results showed evidence of resistance in the B15-1 population and confirmed the susceptibility of B and B15-2 populations.

Mestrado em Engenharia Agronómica - Proteção de plantas - Instituto Superior de Agronomia