In vitro assay selection of glyphosate resistance in lettuce

Glyphosate-resistant plants of 'South Bay' lettuce (Lactuca sativa L.) were produced by using Agrobacterium tumefaciens containing a plasmid carrying glyphosate oxidase and EPSPS gene. An in vitro assay was performed to determine the sensitivity of 'South Bay' leaf discs and seedling explants to varying glyphosate concentrations. The I-50 for glyphosate leaf discs was 53.8 mu M and for glyphosate seedlings 7.6 mu M. There was a high correlation between the response of leaf discs and seedlings to glyphosate based on dry weight. These findings will allow identification of glyphosate-resistant transformants in an early stage of plant development, saving time and reducing the cost in generating an improved cultivar with the glyphosate resistance trait.