A SEED BIOASSAY TO IDENTIFY ACETYL-COA CARBOXYLASE INHIBITOR RESISTANT WILD OAT (AVENA-FATUA) POPULATIONS

A seed bioassay was developed and tested for the rapid identification of aryloxyphenoxypropionate (APP) and cyclohexanedione (CHD) resistanc e in wild oat. Two susceptible (S) genotypes, UM5 and Dumont, were tre ated with fenoxaprop-P and sethoxydim over a range of dosages on filte r paper and agar. The former is a wild oat line and the latter a tame oat cultivar. Within 5 d, shoot and root development of both genotypes were completely inhibited by 10 mu M fenoxaprop-P and 5 mu M sethoxyd im. These dosages were then tested to determine if they were suitable for distinguishing between resistant (R) and susceptible (S) plants, A gar medium was preferred over filter paper because of the ease of prep aration and maintenance. Four known R wild oat populations were includ ed in the tests. Those with high levels of resistance produced signifi cantly longer coleoptiles and roots than S genotypes, but those with m oderate or low levels of resistance could not be separated statistical ly from S biotypes based on quantitative measurements. However, after exposing the germinating, treated seeds to light for 24 to 48 h, all t he R populations produced green coleoptiles and initiated a first leaf , unlike the S genotypes which did not turn green or produce any new g rowth. This procedure proved useful in discriminating between R and S genotypes and in ranking populations in terms of relative levels of re sistance.