Development of imidazolinone herbicide tolerant borage (Borago officinalis L.)

- Borage is commercially cultivated for gamma-linolenic acid (GLA, 18:3-6,9,2), a nutraceutical fatty acid used in food and cosmetics.
- However, an herbicide-resistant variety for effective weed management has not yet been developed, which severely constrains the borage framing.
- This manuscript reports generation of two borage mutant lines resistant to herbicide imidazolinone by ethyl methanesulfonate (EMS) mutagenesis.
- Molecular analysis of the mutant lines revealed single nucleotide substitution inside two acetohydroxyacid synthase (AHAS) genes.
- A KASP marker was thus developed to differentiate the homozygous susceptible, homozygous resistant and heterozygous borage plants.
- An in vitro assay further showed that homozygous resistant borage carrying the AHAS1 mutation retained significantly higher AHAS activity than susceptible borage across different imazamox concentrations.

Borage (Borago officinalis) is an annual herb that produces a high level of gamma-linolenic acid (GLA) in its seed oil. Due to the recognized health benefits of GLA, borage is now commercially cultivated worldwide. However, an herbicide-tolerant variety for effective weed management has not yet been developed. Here we report the generation and characterization of ethyl methanesulfonate (EMS) induced borage mutant lines tolerant to the herbicide imidazolinone. An EMS-mutagenized borage population was generated by using a series of concentrations of EMS to treat mature borage seeds. Screening of the M2 and M3 borage plants using an herbicide treatment resulted in the identification of two imidazolinone-tolerant lines. Sequence analysis of two acetohydroxyacid synthase (AHAS) genes, AHAS1 and AHAS2, from the mutant (tolerant) and wild type (susceptible) borage plants showed that single nucleotide substitutions which resulted in amino acid changes occurred in AHAS1 and AHAS2, respectively in the two tolerant lines. A KASP marker was then developed to differentiate the homozygous susceptible, homozygous tolerant and heterozygous borage plants. An in vitro assay showed that homozygous tolerant borage carrying the AHAS1 mutation retained significantly higher AHAS activity than susceptible borage across different imazamox concentrations. A herbicide dose response test indicated that the line with the AHAS1 mutation could tolerate four times the normally used field concentration of “Solo” herbicide.