Physiological basis for tolerance of fourZea mayshybrids to RPA 201772

Abstract

Greenhouse and laboratory experiments were conducted to determine the physiological basis for differential tolerance of fourZea maysL. hybrids to RPA 201772. Differences inZea maystolerance were quantified by determining the herbicide rate required to injure and reduceZ. maysheight 50% (GR50). GR50values indicated that theZ. mayshybrids ‘Pioneer 3751’ and ‘Pioneer 3737’ were less tolerant to RPA 201772 than the hybrids ‘Pioneer 3394’ and ‘Pioneer 3963.’ Experiments using14C-RPA 201772 were conducted to determine if hybrid sensitivity was due to differential uptake, translocation, or metabolism of the herbicide. Differences in hybrid tolerance were primarily due to differential herbicide metabolism rates. The time required for 50% inactivation (T½) of RPA 201772 was 42 and 52 h for the more tolerant hybrids and 66 and 93 h for the more sensitive hybrids. Increased uptake of RPA 201772 was also a contributing factor to the sensitivity of one of the hybrids.