Rapid test for Detecting Haloxyfop-R methyl Ester Resistance in Winter Wild Oat (Avena ludoviciana durieu)

Detection of resistance to an herbicide in a putatively resistant accession requires a series of experiments which are capable of illustrating the response of the accession to various herbicide doses. Whole plant bioassay in pots usually takes approx. 2 months to obtain the results, thus, rapid tests were developed to accelerate the process. Although determination of discriminating concentration as well as conduction of rapid test for some ACCase inhibitors has been performed by various researchers, no reports are available in this regard for haloxyfop-R methyl ester herbicide in winter wild oat. Thus, the following study was conducted with the objective of rapid detection of resistance to the mentioned herbicide in this weed using the rapid test.

The experiment was conducted using the seeds of 7 putatively resistant winter wild oat accessions and a susceptible biotype gathered from canola farms of Kalaleh Township located in Golestan province in 2015. Rapid test in petri dishes was conducted as a completely randomized design with three replications, with each petri dish as one replicate. To determine the discriminating concentration, various concentrations of haloxyfop-R methyl ester was applied on the susceptible accession and then, all putative accessions were screened using this concentration. The biotypes of the studied weed were exposed to various doses of the herbicide in the petri dish bioassay to determine the resistance factor. Also, a completely randomized design experiment with three replications was conducted for screening of putative accessions in the greenhouse. Accessions which maintained their survival and dry weight respectively 50 and 80 percent compared to the unsprayed control were selected. A whole plant dose-response bioassay was also done separately for each biotype.

Discriminating concentration of haloxyfop-R methyl ester for winter wild oat was obtained 0.106 mg ai. L-1. According to the results, 5 out of 7 accessions were detected as resistant and underwent the concentration- response assay in petri dishes. Resistant factors of the biotypes in the rapid test ranged from 2783.054 to 3421.414. However, no significant difference was observed among the biotypes. According to the results of the greenhouse, 5 accessions were detected as resistant with resistance factors of 14.19 to 18.54, with no significant difference among the biotypes. There was a positive and significant correlation between the results obtained from the rapid test with the greenhouse assay, which indicates the validity of the Petri dish assay.

The results of the rapid test are in accordance with those of the whole plant assay in pots. Therefore, putative winter wild oat accessions collected from the region may be screened using the obtained concentration of haloxyfop-R methyl ester (0.106 mg ai. L-1) and resistant biotypes may be detected more rapidly compared to greenhouse assays. Due to the swift development of herbicide resistance issue, rapid detection of resistance is essential. Thus, using methods such as rapid test may be very feasible.