Patterns of resistance to ALS herbicides in a resistant limnocharis flava (L.) buchenau population from Malaysia

Abstract

Sawah Flowering Rush (Limnocharis flava (L.) Buchenau) is a monocot weed in the Alismataceae family. Limnocharis flava is a common and competitive weed in irrigated and rain fed lowland rice fields in Malaysia (Juraimi et al. 2012; Weber and Brooks 2013). In Malaysia this weed first evolved multiple i resistance to herbicides in the Groups B/2, and 0/4 in 1998 in Pulau Pinang and is now infesting many rice fields, predominantly during the main planting season. This particular population has been confirmed to develop resistance to 2, 4-D and bensulfuron- methyl (Juraimi et al. 2012) and it is believed that they may be already cross-resistant to other herbicides in the Groups B/2, and 0/4 (Heap 2016). The present study aims to characterize resistance patterns across ALS inhibitors in a Limnocharis flava population collected in Pulau Pinang, Malaysia. Dose-response experiments were conducted to determine the level of resistance to the ALS herbicides sulfonylureas (SU), imidazolinone triazolopyrimidine (TP) and pyrimidinyl- thiobenzoate (PTB). Cross resistance across different ALS herbicides was observed in resistant L. flava population; exhibiting high- level resistance to bensulfuron-methyl, while exhibiting moderate- level of resistance to metsulfuron- methyl and low- level of resistance to pyrazosulfuron- ethyl and pyribenzoxim. However, similar to susceptible population, all resistant L. flava individuals were sensitive towards ALS herbicides imazethapyr, penoxsulam, and bispyribac- sodium. The finding from this study is crucial to elucidate the underlying resistance mechanism that conferred resistance to ALS herbicides in L. flava. In this study, resistant population of L. flava exhibited high level of resistance to bensulfuron- methyl, while at the same time were cross-resistant to other SU and PTB herbicides at varied levels. Thus, the resistance is likely endowed by target site mutation(s). The mechanism endowing resistance in R L. flava remains unknown and a comprehensive study to elucidate this aspect is underway.