PINTO BEAN (PHASEOLUS-VULGARIS) VARIETAL TOLERANCE TO IMAZETHAPYR

Field and laboratory studies were conducted to determine if difference s existed in pinto bean varietal tolerance to postemergence applicatio n of imazethapyr under field conditions; if differences in tolerance w ere due to differential acetolactate synthase enzyme sensitivity or di fferences in C-14-imazethapyr absorption, translocation, and metabolis m; and the heritability of imazethapyr tolerance in pinto bean. All ra tes of imazethapyr injured Olathe, Sierra, UI-114, P89405, Aztec, and P90570 pinto bean varieties 7 d after treatment in 1991 and 1992, exce pt 53 g ai ha(-1) of imazethapyr applied to Sierra pinto bean in 1991. Olathe was injured more than other varieties in 1991, and physiologic al maturity of Olathe was delayed more than Sierra in 1991 and 1992. S eed yields of all varieties were not reduced in 1991, and only P90570 had reduced seed yields from 53 g ha(-1) of imazethapyr in 1992. Diffe rential sensitivity of the acetolactate synthase enzyme to imazethapyr was not the mechanism of differential varietal response. Olathe pinto bean absorbed and translocated 1.4 and 1.3 times more C-14-imazethapy r, respectively, than Sierra pinto bean 24 h after application. No dif ferences in C-14-imazethapyr metabolism were detected between Olathe a nd Sierra pinto bean. Broad heritability of imazethapyr tolerance in p into bean was calculated to be 0.85. The number of genes controlling t he inheritance of imazethapyr tolerance in pinto bean was greater than one.