Development of 2,4-D-resistant transgenics in Indian oilseed mustard (Brassica juncea)

Abstract

Transgenic lines resistant to the herbicide 2,4- dichlorophenoxyacetic acid (2,4-D) were developed in mustard (Brassica juncea), a major oilseed crop grown in more than six million hectares of land in North India. The developed construct contained the tfdA gene, encoding the enzyme 2,4-D monooxygenase, cloned downstream to the 35S promoter along with a leader sequence from RNA4 of alfalfa mosaic virus (AMV leader sequence), for improved expression of the transgene in plant cells. Southern analysis of T0 transgenics confirmed six out of 24 transgenics to be single copy events, from both the flanks of T-DNA. Selfed progeny derived from single copy tfdA lines germinated normally and rooted in medium containing 2,4-D at concentrations as high as 2.5 mg l^–1 compared to the wild-type seedlings which did not root even at a concentration of 0.5 mg l^–1. The tfdA transgenic lines were also sprayed with commercially available 2,4-D herbicide at concentrations ranging from 10 to 1000 mg l^–1 under field conditions. Wild type plants were affected by levels as low as 10 mg l^–1 and were completely killed at a concentration of 50 mg l^–1. The four transgenic lines tested in the study were resistant to herbicide concentration of 500 mg l^–1. The available transgenic lines can be used for testing the potential of 2,4-D in weed control including the control of parasitic weeds (Orobanche spp) of mustard and for low-till cultivation of mustard.