Abstract
Haloxyfop is one of two acetyl-coenzyme A carboxylase (ACCase) inhibitors that is recommended for controlling Poa annua. We have characterised a population of P. annua that had developed resistance to haloxyfop. This resistant population was found to be almost 20 times less sensitive to haloxyfop than a susceptible population based on percentage survival of individuals in two dose-response experiments. However, the haloxyfop-resistant population was still susceptible to clethodim. Pre-treatment of resistant individuals with a cytochrome P450 inhibitor, malathion, did not change the sensitivity level of the resistant plants to haloxyfop, suggesting that a non-target site mechanism of resistance involving enhanced metabolism, was not responsible for this resistance in P. annua. Gene sequencing showed that a target site mutation at position 2041, which replaced isoleucine with threonine in the carboxyltransferase (CT) domain of the ACCase enzyme, was associated with resistance to haloxyfop in the resistant population. An evaluation of the 3-D structure of the CT domain suggested that, unlike Asn-2041, which is the most common mutation at this position reported to date, Thr-2041 does not change the conformational structure of the CT domain. This is the first study investigating the molecular mechanism involved with haloxyfop resistance in P. annua.
Highlights
Haloxyfop is one of two acetyl-coenzyme A carboxylase (ACCase) inhibitors that is recommended for controlling Poa annua
100% survival was recorded for the haloxyfop-resistant population (R) when treated with haloxyfop application rates up to 480 g ae ha−1, while 100% mortality was observed for the individuals of the haloxyfop-susceptible population (S) when treated with 120 g ae ha−1 of haloxyfop
Resistance to commonly used herbicides such as EPSP synthase inhibitors, ALS inhibitors and photosystem II inhibitors has been reported in P. annua globally[17]
Summary
Haloxyfop is one of two acetyl-coenzyme A carboxylase (ACCase) inhibitors that is recommended for controlling Poa annua. An evaluation of the 3-D structure of the CT domain suggested that, unlike Asn-2041, which is the most common mutation at this position reported to date, Thr-2041 does not change the conformational structure of the CT domain This is the first study investigating the molecular mechanism involved with haloxyfop resistance in P. annua. Cultural practices that can help desirable species compete well with P. annua can be used for management of this weedy grass species in turf grasses[7]; i.e. in an effort to stop it re-establishing from seed after it completes its life cycle. The non-target site mechanism of resistance to ACCase-inhibitors in weedy grass species involves enhanced herbicide metabolism, mainly through the enzyme cytochrome P45021. Clethodim (CHD) and haloxyfop (APP) are two ACCase-inhibitors that do provide effective control of P. annua[24]
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