Target-site basis for resistance to flucarbazone- sodium in Japanese brome (Bromus japonicus Houtt.) in China

Abstract

Japanese brome ( Bromus japonicus Houtt.) is a troublesome annual weed and widely distributed in winter wheat ( Triticum aestivum L.) fields in the North China Plain. A B. japonicus population (TJ06) suspected of resistance to acetolactate synthase (ALS) inhibitors was found in Tianjin, China. In this study, the TJ06 population with an Asp-376-Glu mutation in ALS gene was identified. TJ06 population developed 66.7-fold resistance to flucarbazone-sodium and exhibited obvious cross-resistance to other two ALS-inhibiting herbicides. The 50% plant growth reduction (GR 50 ) to herbicides of pyroxsulam and mesosulfuron-methyl were 28.72 and 39.44 g ai ha -1 , respectively. In in vitro ALS activity assays, the concentration of flucarbazone-sodium required to inhibit 50% ALS activity (I 50 ) for TJ06 was 11.3-fold greater than that for a susceptible population (TJ01), which was highly correlated with that of whole-plant response experiments and indicated that the Asp-376-Glu mutation leading to resistance reduced sensitivity of the ALS enzyme to flucarbazone-sodium. Besides, one derived cleaved amplified polymorphic sequence (dCAPS) marker was designed to quickly detect Asp376 mutation in ALS gene of B. japonicus . of Bromus japonicus has evolved high-level resistance to flucarbazone, and demonstrates the molecular mechanism underlying this resistance by an Asp-376-Glu mutation in the ALS gene. These results demonstrate that persistent and intensive application of flucarbazone-sodium has resulted in resistance in B. japonicus in China, and an integrated weed management system is highly necessary for B. japonicus control in wheat fields.