Resumen
- The buildup of propanil-resistant Echinochloa colona biotypes in Colombia rice fields has been documented, and is associated to the repeated use of propanil. Dose-response data previously collected were re-interpreted using non-linear regression, and fitted to a four-parameter logistic model, which allowed to estimate GR50 value for the least and most resistant populations were 0.37 and > 4 kg propanil/ha, respectively. HPLC studies with plant extracts from propanil resistant and susceptible plants showed that resistant plants were able to metabolically degrade propanil to a greater extent than susceptible plants. However in 30-40 days-old plants a different mechanism for resistance may prevail, which could imply another possibility for cross resistance with other herbicides, a realistic situation given that farmers in Colombia often spray propanil to heterogeneous E. colona populations, when young and older plants coexist. An in-vitro test was developed to assay samples of E. colona leaves from the field, this is an essential tool that will be used in the monitoring of resistance in Colombian rice fields, within the framework of activities to be conducted by the newly created Task Force for Herbicide Resistance Monitoring in Colombia (part of COMALFI), the Colombian society for plant physiology and weed science). Future work should study the possible patterns of cross resistance, and develop concepts to overcome the problem.