Evaluation of glyphosate resistance in transgenic lettuce

Six transgenic 'South Bay' lettuce lines (Lactuca sativa L.) with elevated levels of 5-enolpyruvyl shikimate-3-phosphate synthase (EPSPS) were evaluat ed for tolerance to the herbicide glyphosate, The six lines were selected f rom approximate to 150 independent transformation events using and Agrobact erium tumefaciens system. Three assay methods were used to identify gene ex pression with regard to glyphosate resistance. Leaf disks: of the transgeni c lines were cultured on media containing 0 to 1280 muM glyphosate, Leaf di sks of the control had lower dry weight (DW) at 40 muM and greater glyphosa te than all the transgenic lines. The transgenic lines continued to grow ev en at 1280 muM. Plants 21 days old were sprayed in the greenhouse with rate s of glyphosate at 0 to 35.84 kg.ha(-1). DW of all the lines were similar t o the control, with a few exceptions, at glyphosate concentrations from 0 t o 0.56 kg.ha(-1). At 2.24 to 8.96 kg.ha(-1) all of the transgenic lines had DW greater than the control, while at 17.92 and 35.84 kg.ha(-1) only B-32, B-33, C-3, and C-14 had DW greater than the control. The resistant line fr om the greenhouse experiment, B-32, grew normally in field trials at the hi ghest glyphosate rate, 17.92 kg.ha(-1), while control plants died at 0.55 k g.ha(-1) glyphosate, Lines A-11 and C-3 had lower DW than B-32 at 2.24 kg h a(-1) glyphosate and greater, While Leaf disk assays can identify potential transformed lines expressing the EPSPS and glyphosate oxidase (GOX) gene, and greenhouse screening can evaluate seedling vigor after glyphosate appli cation, field trials are necessary to evaluate plant growth and yield throu gh the growing season. Chemical name used: N-(phosphono-methyl) glycine (gl yphosate).