Physiological responses of resistant and susceptible rice cultivars to HPPD-inhibiting herbicides

The objectives of this research were to quantify resistance levels in different rice biotypes to HPPD-inhibiting herbicides, benzobicyclon, mestrione, and tefuryltrione and determine mechanisms of resistance of benzobicyclon in different rice biotypes. In terms of shoot fresh weight, japonica-type, Ilmibyeo and Baekokchal were 17-and 53-73-fold more resistant to benzobicyclon and mestrione, respectively, than indica x japonica-type, Hyangmibyeo-1 and Dasanbyeo. However, responses of shoot fresh weight in rice cultivars of japonica-type to tefuryltrion were similar to those of indica x japonica-type. Carotenoids and chlorophylls contents of the japonica-type, Iilmibyeo and Baekokchal were also less affected by the benzobicyclon, than the indica x japonica-type, Hyangmibyeo-1 and Dasanbyeo. The levels of MDA and H₂O₂ in rice cultivars of indica x japonica-type after benzobicyclone treatment were much higher than those of rice cultivars of japonica-type. Thus, the resistance in rice cultivars of japonica-type may be caused by the result of less lipid peroxidation, less H₂O₂, higher carotenoid and chlorophyll contents when exposed to HPPD-inhibitibg herbicide, benzobicyclon.