Action of Imidazolinones

The I50 for various commercial imidazolinone herbicides in vitro AHAS assays varies between 0.1 and 10 gM depending upon the assay conditions [27]. Under 

Plants tolerant to imidazolinones have been produced by both transgenic and non-transgenic mechanisms. However, all of the imidazohnone-tolerant crops currently being sold have been developed by non-transgenic methods. The first imidazolinone-tolerant crop (maize) was introduced in 1992. Subsequently, four additional imidazolinone-tolerant crops (canola, rice, wheat and sunflower) have been commercialized [31]. All of the imidazohnone-tolerant crops are being sold under the CLEARFIELD trade name. 

These imidazolinone tolerance traits in different crops were developed by various methods. These methods included tissue culture selection (maize), pollen mutagenesis (maize), microspore selection (canola), seed mutagenesis (wheat and rice) and incorporation of resistance trait from a weedy relative (sunflower). Details of these methods have been previously reviewed [31, 32]. In all of these cases, the basis of tolerance is due to the presence of an altered form of AHAS that is resistant to inhibition by imidazolinones. The resistant enzyme is produced due to a single base pair change in the gene encoding the large subunit 

From the imidazolinone family, four different molecules, imazapyr, imazapic, imazethapyr and imazamox, have been registered for weed control in various imidazolinone-tolerant crops in different regions of the world. These herbicides are applied alone or in combination with other imidazolinones or with other classes of herbicides for a broad spectrum, season-long weed control. A combination of different imidazolinone tolerance traits and multiple herbicide options provides an effective weed management tool for farmers around the world. 

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