A pollen test to detect ACCase target-site resistance within Alopecurus myosuroides populations

This study was conducted to determine a suitable medium for in vitro germin ation of Alopecurus myosuroides pollen and to develop a reliable test for t he rapid screening of ACCase target site-resistant plants within population s. The assay is based upon germination of pollen in a medium supplemented w ith ACCase inhibitors. A 0.25% agar medium, containing 200 mg L-1 CaNO3, 10 0 mg L-1 H3BO3, 200 g L-1 sucrose, was selected as a suitable medium for in vitro pollen germination. At 25 degrees C, this medium supported a mean ge rmination rate of 85% within two hours. Plants highly resistant (Rh) to ary loxyphenoxypropionate (APP), owing to the expression of an insensitive ACCa se, were found to express this resistance in their pollen. In contrast, pla nts moderately resistant (Rm) to APP herbicides, owing to an enhanced capac ity to detoxify herbicides, did not exhibit this resistance in their pollen . Concentrations of 120 mu M fenoxaprop and 1000 mu M clodinafop were selec ted as the best for reliable discrimination of the target-site-resistant bi otypes. At these concentrations there was more than 50% germination of the Rh pollen grains whereas less than 10% of the S and Rm pollen grains germin ated. This test, using haploid material, may also permit distinction betwee n homozygous- and heterozygous-resistant individuals.