Bull. Spec. CORESTA Symposium, Kallithea, 1990, p. 148, A39, ISSN.0525-6240

Use of bromoxynil for weed-killing of transgenic tobaccos

Rhone-Poulenc Agrochimie, Lyon, France
Bromoxynil is a post-sprouting anti-dicotyledon herbicide used for weed-killing of cereal crops. This selectivity results from the detoxication of the herbicide by a nitrilase. A gene coading for this enzyme has been isolated from a Klebsiella ozaenae, subjected to the control of regulation sequences functioning in the plants, inserted between the edges of DNA-T of Agrobacterium tumefaciens and then introduced into industrial tobaccos by the method of co-culture of leaf discs. Initial trials carried out under glass and then in the field have shown that small quantities of nitrilase confer resistance to at least 16 times the commonly used dose of the herbicide. This level of resistance was obtained particularly by using a construction involving the promoter of a small subunit of the sunflower Rubis Co. Since this resistance has been acquired, three types of complementary trials have been carried out : 1) Development trials have defined a weed-killing program for tobacco. In view of the selectivity of bromoxynil, association with a post-sprouting anti-monocotyledon herbicide was tested. This association, which is fully selective for tobacco, gave good weed-killing efficacy against a range of adventices. 2) Metabolism trials have shown that the degradation of the herbicide follows a pathway similar to that described for wheat. At harvesting, the herbicide and its metabolites are below the threshold of detection (less than 0.5 mg/kg fresh weight). 3) Finally, trials carried out to confirm the compliance of treated and untreated transgenic tobaccos with regard to agronomic and quality parameters of the raw material have demonstrated the absence of any harmful effects of the transformation and the treatment on the basis of the analysis criteria adopted. The efficacy and cost of this weed-killing program compared with those of traditional weed-killing programs make bromoxynil a potential herbicide for transgenic industrial lines.