Transgenic sugar beet tolerant to glyphosate

Sugar beet (Beta vulgaris L.) lines transformed with the 5-enolpyruvylshikimate-3-phosphate synthase gene (CP4 EPSPS) from Agrobacterium sp. CP4 and a glyphosate oxidase reductase gene (GOX) also isolated from bacteria resulted in the development of lines highly tolerant to glyphosate. Glyphosate (N-phosphonomethyl-glycine) is the active ingredient in Roundup(R), herbicide. The EPSPS enzyme is involved in the biosynthesis of aromatic amino acids. Glyphosate binds irreversible to the EPSPS and inhibits the pathway. GOX degrades, glyphosate into non-toxic compounds. 260 independent transformants have been evaluated in greenhouse and field trials for tolerance to Roundup(R) in 1993 and 1994. Variation of tolerance was recorded between different transformants, ranging from complete susceptibility to full tolerance. The Agrobacterium tumefaciens mediated transformation resulted in a negative correlation between copy number of the T-DNA insert and the level of tolerance to the herbicide. Transformants which contain a single copy insert showed tolerance to higher doses of glyphosate than transformants with multiple copies. Two transgenic lines were identified that showed agronomically useful tolerance to glyphosate.