04 July 2016

#163 Herbicide and insect resistant crops

Genetic technology can provide benefits in, for example, agriculture and medicine, but has the associated risk of the escape of the gene concerned into organisms other than the intended host.

Herbicide resistant crops
Fields of crops are sprayed with herbicide to kill weeds that compete for space, light, water, and ions to increase crop yield.

Oil seed rape

  • a source of vegetable oil and biodiesel fuel
  • modified oil seed rape is resistant to the herbicide glyphosphate (inhibits the synthesis of 3 amino acids: phenylamine, tyrosine, trytophan)
             - glyphosphate is absorbed through leaves and is transported to growing tips
  • the gene transferred into crop plants come from a strain of the bacterium Agrobacterium

  • resistant to herbicides: sulfonylurea and dinitroaniline
  • genes taken from other plant species

Effects on the environment:
  • the GMed plants become agricultural weeds
  • pollen will transfer the gene to wild relatives, producing hybrid offspring that are invasive weeds
  • herbicide-resistant weeds will evolve because so much of the same herbicide is used

Insect-resistant crops
To protect crop plants against insect pests to increase crop yield

Cotton - protected against boll weevil

Bt maize - protected against corn borers
  • Bt toxing is - lethal to insects that eat it
                              - harmless to other animals
  • gene for Bt toxin is taken from the bacterium Agrobacterium tumefaciens
  • genetically modified crop plants with Bt toxin gene produce their own insectisides
  • Bt resistance in corn borers: recessive allele. Adult corn borers in refugees (non GM maize) supply the dominant allele to counteract the resistance when they mate with borers from the fields

Effect on environment:
  • evolution of resistance by insect pests
  • damaging effects on other insect species
  • transfer of added gene to other plant species

Syllabus 2016-2018

19.3 Genetically modified organisms in agriculture 

The ability to manipulate genes has many potential benefits in agriculture, but the implications of releasing genetically modified organisms (GMOs) into the environment are subject to much public debate in some countries.

a) explain the significance of genetic engineering in improving the quality and yield of crop plants and livestock in solving the demand for food in the world, e.g. Bt maize, vitamin A enhanced rice (Golden riceTM) and GM salmon 

b) outline the way in which the production of crops such as maize, cotton, tobacco and oil seed rape may be increased by using varieties that are genetically modified for herbicide resistance and insect resistance 

c) discuss the ethical and social implications of using genetically modified organisms (GMOs) in food production


  1. Oil seed rape genetically modified to have resistance to herbicide glyphosate (spelling error - glyphosphate)

  2. Gene for Bt toxin is taken from the bacterium Bacillus thuringiensis not Agrobacterium tumefaciens (which is the bacterium used in the making of Golden Rice)