Identification of Lolium rigidum gaud. biotypes resistant to the clodinafop propargyl herbicide in wheat fields of Golestan province

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 in clodinafop propargyl herbicide in rigid ryegrass from wheat field of Golestan province. 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 experiments were conducted using the seeds of 30 putatively resistant rigid ryegrass accessions and a susceptible biotype gathered from wheat field of Golestan province in 2019. 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 clodinafop propargyl was applied on the susceptible accession and then, all putative accessions were screened using this concentrations. 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, another experiment based on a completely randomized design 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. Checking the distribution map of resistant biotypes indicated that these biotypes were not uniform in the wheat fields of Golestan province. During sampling, geographical coordinates of infected areas were recorded using GPS Map60 device and weed distribution map was prepared using ArcGIS software.

Discriminating concentration of clodinafop propargyl for rigid ryegrass was obtained 0.0196 mg ai. L-1. According to the results, 25 out of 30 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 38.75 to 1756.20. According to the results of the greenhouse, 25 accessions were detected as resistant with resistance factors of 11.58 to 24.05. There was a positive and significant correlation between the results obtained from the rapid test with the greenhouse assay (%93). Investigation of distribution map of resistant biotypes indicated non-even distribution of these biotypes across wheat fields of Golestan province, with resistant and susceptible biotypes often observed in the west and east of the province, respectively.

Putative rigid ryegrass accessions collected from the region may be screened using 0.0196 mg ai. L-1 concentration and resistant biotypes may be detected more rapidly compared to greenhouse assays. Also, the results of the rapid test are in accordance with those of the whole plant assay in pots. Due to the swift development phenomenon of herbicide resistance issue, rapid detection of resistance is essential. Thus, using methods such as rapid test may be very feasible.