Assessment of Wild Mustard (Sinapis arvensis L.) Resistance to ALS-inhibiting Herbicides

There is an urgent need for rapid, accurate, and economical screening tests that can deter‐ mine if weeds surviving a herbicide application are resistant. This chapter describes de‐ velopment and application of a simple root length bioassay technique for detection of wild mustard (Sinapis arvensis L.) resistance to ALS-inhibiting herbicides. This bioassay was performed in 2-oz WhirlPak® bags filled with 50 g of soil wetted to 100% moisture content at field capacity. Wild mustard seeds were pre-germinated in darkness in Petri dishes lined with moist filter paper for 2 days. Six seeds with well-developed radicles were planted in the non-treated soil and in soil with added herbicide, and plants were grown in a laboratory under fluorescent lights. After 4 days of growth, WhirlPak® bags were cut open, soil was washed away, intact plants were removed, and root length was measured with a ruler. The concentration of each herbicide in soil at which a significant root inhibition of susceptible biotype, but no root inhibition of a resistant biotype occur‐ red was selected. Susceptibility/resistance of wild mustard populations was estimated by calculating the percentage of uninhibited roots of plants grown in the herbicide-treated soil as compared to the plants grown in the non-treated soil.