Determination of resistance level and multi-resistance to pendimethalin of weed Solanum nigrum L. in Xinjiang cotton fields

In order to clarify the resistance level of weed Solanum nigrum L. to pendimethalin and its multi-resistance to other commonly used soil-treatment herbicides in Xinjiang cotton fields, 56 S. nigrum populations from different regions of Xinjiang were tested by the petri dish method and the whole plant method and the differences between the two detection methods were compared. According to the results of the whole plant method, three populations of sensitive (SHZ-8), medium resistance (CJ-2), and high resistance (BL-1) were selected to determine multi-resistance to prometryn, oxyfluorfen, and flumioxazin, respectively. The result showed that the resistance trend of the two methods was the same, and the resistance level of S. nigrum showed northern Xinjiang > southern and eastern Xinjiang, but the resistance index measured by the petri dish method was generally lower than that by the whole plant method. The results of the petri dish method showed that sensitive, low-resistance, medium-resistance, and high-resistance populations accounted for 12.5%, 71.4%, 12.5%, and 3.6% of the total populations, respectively. Whereas the corresponding ratios of the whole plant method were 5.4%, 73.2%, 16.0%, and 5.4%. The results of both methods are consistent and indicate that the resistance of S. nigrum to pendimethalin in Xinjiang cotton fields was mostly low to medium resistance. Compared with the sensitive population SHZ-8, the BL-1 population showed the highest relative resistance in both methods: the GR₅₀ value tested by the petri dish method was 90.30 mg/L and the resistance index was 20.62; the GR₅₀ value tested by the whole plant method was 4805 g/hm² and the resistance index was 26.20. The multi-resistance study found that the BL-1 population had multi-resistance to flumioxazin, while the WJQ-2 population did not develop multi-resistance to prometryn, oxyfluorfen, and flumioxazin.