Baseline sensitivity of Scirpus juncoides and Monochoria vaginalis populations to HPPD inhibitors in Korea

Abstract

The study was conducted to evaluate the baseline sensitivity index (BSI) of Scirpus juncoides and Monochoria vaginalis populations to 4-hydroxyphenylpyruvate dioxygenase (HPPD) inhibitors, benzobicyclon, and mesotrione and to estimate the potential risk of the HPPD inhibitor resistance in paddy fields in Korea. The seeds of matured S. juncoides and M. vaginalis biotypes were collected from a total of 105 sites and a whole plant dose-response test was performed. Nonlinear fit curve (DoseResp) analysis revealed that GR50 values of S. juncoides biotypes ranged from 9.6 to 16.5 g a.i. ha-1 to mesotrione and 13.1 to 26.4 g a.i. ha-1 to benzobicyclon. BSI was 1.72 and 2.01 for mesotrione and benzobicyclon respectively. The GR50 values of M. vaginalis populations ranged from 10.9 to 16.3 g a.i. ha-1 to mesotrione and 11.7 to 21.1 g a.i. ha-1 to benzobicyclon. BSI was 1.48 for mesotrione and 1.78 for benzobicyclon. No shift in mesotrione and benzobicyclon sensitivity was observed suggesting that these HPPD herbicides can still be used very ffectively to control S. juncoides and M. vaginalis populations in rice fields in South Korea. However, we strongly suggest that constant monitoring and baseline sensitivity studies need to be conducted continuously to detect the evolution of herbicide-resistant weed biotypes.