Tracing Wild Mustard (Sinapis arvensis L.) Accessions Resistant to Tribenuron-methyl in Wheat Fields of Ramhormoz and Preparing Distribution Map of Resistant Fields

Wild mustard (Sinapis arvensis L.) is a very common weed within cereal and rapeseed fields in Iran and many other countries. This weed is usually controlled by tribenuron-methyl in wheat fields of Iran. However, due to consecutive application of tribenuron-methyl for the last 27 years in wheat fields, control failures were reported by farmers. Resistance to ALS inhibiting herbicides is the most common form of herbicide resistance in the world. So far, 165 resistant biotypes to this family have been reported. Therefore, present study was carried out to survey suspected of resistance wild mustard accessions to tribenuron-methyl in wheat fields of Ramhormoz and preparing distribution map of resistant fields.

An experiment was conducted in Agricultural Sciences and Natural Resources University of Khuzestan during 2017-2018. 22 no. of the suspected resistance wild mustard accessions to tribenuron-methyl were gathered from wheat fields of the Ramhormoz. One susceptible accession was also gathered from a field with no history of spraying. Pot experiments were carried out in two stages including the initial screening with the recommended dose of tribenuron-methyl (15 g ai ha-1) and dose-response assay that accessions were investigated for the effect of tribenuron-methyl on dry weight and survival plant no. under outdoor conditions. The plants per pots were sprayed, based on tribenuron-methyl dose (0, 0.125, 0.25, 0.5, 1, 2, 4, 8, 16, and 32-fold of recommended dose). The shoot dry weight data were converted to a percentage based on control plants data within each accession. A log-logistic curve with three and four-parameters was used to describe dose–response relationships. Dry-weight data were fitted to a nonlinear log-logistic regression model using the package drc in the statistical program R (R Development Core Team, 2008). The distribution map of the resistant populations was plotted using ArcGIS 10.3 software.

Screening results showed that nine accessions (B, C, H, P, S, T, W, X, U) were strongly resistant (R) and 10 accessions (A, E, F, G, K, L, M, O, Q, R) were probably resistant (PR or RR), and three accessions (D, N and Y) were susceptible (S) or suspected resistance (SR) to tribenuron-methyl based on Adkins and Mo‘s 's ranking system. While, Screening results based on Mo‘s 's ranking system showed that nine accessions (B, C, H, P, S, T, W, X, U) were completely resistant (RRR) and 10 accessions (A, E, F, G, K, L, M, O, Q, R) were probably resistant (RR), and two accessions (D and N) were suspected resistance (SR) and one population (Y) was susceptible to tribenuron-methyl. With increasing doses of the herbicide tribenuron-methyl, the dry weight of susceptible and susceptible accessions decreased during the sigmoid process. Resistance factor of accessions (W, U, X, S, B, C, T, K, R, G, Q, O, E, A, P, M, F, H, and L) based on dry weight (% of control) and survival (% of control) ranged from 1.10- 8.17 and 2.08-7.60, respectively. A different resistance factor was observed between the accessions; thus, the W accession with the highest resistance factor of 8.17 and 7.60 and the L accession with the lowest resistance factor of 1.10 and 2.80 based on dry weight and survival (% of control) were resistant to the herbicide tribenuron-methyl. While 6.80 g ai ha-1 caused a 50% reduction in the dry weight of the susceptible Z accession, this reduction was calculated to be 60.55 g ai ha-1 for the most resistant accession (W), which differed significantly based on the calculated confidence limits. A map of the distribution of contaminated fields of resistant wild mustard accessions using GIS showed that most resistant accessions were observed in eastern and southeastern regions of Ramhormoz.

The results of this experiment confirmed the presence of resistance in wild mustard accessions to tribenuron-methyl. Repeated use of tribenuron-methyl in wheat fields of Ramhormoz is one of the most important reasons for resistance in these fields. Distribution map makes it possible to predict farms infected with resistant accessions and help prevent the recommendation and use of ALS inhibiting herbicides in these farms, so that in order to break the resistance in resistant accessions and it will be effective reduce the use of herbicides. Therefore, the use of distribution maps can be used to implement integrated weed management programs and to prevent the development of resistance accessions in other areas.