EFFECTS OF IMAZAMETHABENZ ON THE MAIN SHOOT GROWTH AND TILLERING OF WILD OAT (AVENA-FATUA L)

Foliar application of imazamethabenz at sublethal doses of 100 and 200 g a.i./ha to wild oat plants at the two-leaf stage without tillers gr eatly inhibited the growth of the main shoot but increased tillering. The near cessation of sheath and the main stem elongation indicated th at the major effect of imazamethabenz on the main shoot was inhibition of intercalary growth. Low doses of imazamethabenz treatment resulted in more leaves (including leaf primordia) in the main stem but did no t affect mature first and second leaves. Sublethal doses of imazametha benz only briefly inhibited tiller growth. A later increase in tilleri ng in treated plants resulted from the stimulated resumed growth of ti llers and the increased initiation of tiller buds. Such enhanced tille ring mainly resulted from the release of apical dominance due to the i nhibition or cessation of the main stem growth with imazamethabenz tre atment. Both doses of imazamethabenz (100 and 200 g a.i./ha) significa ntly reduced the biomass of shoots and roots, but increased the ratio of roots/shoots dry weight.