A rapid reliable test for screening aryloxyphenoxy-propionic acid resistance within Alopecurus myosuroides and Lolium spp. populations

A reliable seedling bioassay was developed and tested for the rapid screeni ng for resistance to aryloxyphenoxypropionic (APP) herbicides in Alopecurus myosuroides and Lolium spp, populations. It is based upon the difference i n coleoptile length of resistant and susceptible A. myosuroides and Lolium seedlings, respectively, exposed to fenoxaprop-P acid and diclofop acid sol ution for 6 days in a plastic box. A 6 mg L-1 fenoxaprop-P acid solution wa s selected as the best concentration for a reliable screening of resistant biotypes within A. myosuroides populations. At this concentration, coleopti le lengths of susceptible and resistant seedlings were shorter and longer t han 10 mm respectively. Similarly, resistant seedlings within Lolium popula tions were easily detected at 10 mg L-1 diclofop acid. At this concentratio n, coleoptile lengths of susceptible and resistant seedlings were shorter a nd longer than 20 mm respectively. For both populations, the coleoptile len gth distributions appear to discriminate between two kinds of APP-resistant biotypes (highly and slightly resistant).