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 deter mine the sensitivity of 'South Bay' leaf discs and seedling explants to var ying 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 b etween the response of leaf discs and seedlings to glyphosate based on dry weight. These findings will allow identification of glyphosate-resistant tr ansformants in an early stage of plant development, saving time and reducin g the cost in generating an improved cultivar with the glyphosate resistanc e trait.