Field Survey and Resistance Occurrence to ALS-Inhibiting Herbicides in Glebionis coronaria L. in Tunisian Wheat Crops.

Glebionis coronaria (L.) Cass. ex Spach is a troublesome weed in cereal cropping systems in northern Tunisia. Recently, failures in controlling this weed have been reported by farmers. Field surveys and farmers interviews were conducted to highlight the potential causes of G. coronaria occurrence and the associated yield losses in wheat. Survey results revealed a significant correlation between farmers' awareness of resistance occurrence and cultural practices, mainly sowing date and tillage, while G. coronaria abundance was related to the lack of herbicide rotation and the frequency of ALS-inhibiting herbicide use. High G. coronaria infestations (more than 20 plants/m(2)) caused a significant decrease in wheat grain yield, reaching almost 75% at a density of 100 plants/m(2). Field and pot experiments showed low efficacies of ALS-inhibiting herbicides to control G. coronaria populations. The application of field rates of tribenuron-methyl and mesosulfuron + iodosulfuron failed to control the tested populations, and generally, G. coronaria dry weight increased compared to nontreated ones (potential hormetic effect). These findings were further investigated in two selected resistant populations through tribenuron dose-response experiments, plants from both populations exhibited high resistance factors (greater than 300), surviving up to 16-fold the recommended field dose. This is the first report for G. coronaria resistance occurrence to ALS-inhibiting herbicides in Tunisia and the second case worldwide.