Effect of glyphosate on the castor plant Ricinus communis L

Authors: McKeon, Thomas; Brichta, Jenny

Submitted to: Biocatalysis and Agricultural Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/24/2014
Publication Date: 3/24/2014
Citation: Mckeon, T.A., Brichta, J.L. 2014. Effect of glyphosate on the castor plant Ricinus communis L. Biocatalysis and Agricultural Biotechnology. DOI: 10.1016/j.bcab.2014.03.002.

Interpretive Summary: Castor oil is an extremely useful chemical feedstock, used in an array of products that match and are superior to similar products currently derived from petroleum and castor plants can produce the equivalent of 6 barrels of petroleum per acre. However, castor contains a protein toxin and there is concern about the possibility of castor volunteer plants appearing in other fields and getting mixed in with food crops. In most cases, simple field observation can eliminate castor volunteers, as castor plants are 5 to 6 feet in height, but such volunteers could be hidden in a corn field. Since most corn grown in the US is resistant to glyphosate, we evaluated the effect of this herbicide on castor at two different growth stages. Under a standard treatment for glyphosate-resistant corn, nearly all of the inflorescences on the castor plant were killed and the seed that developed was approximately 98% inhibited in germination. Early treatment of fields will be effective in preventing castor volunteer plants from mixing in with food crops.

Technical Abstract: The presence of a toxin in the castor seed has been a major impediment to the reintroduction of castor as a domestic crop in the US. Because dehiscent forms of castor are invasive and castor seed remains viable for years under the right conditions, there is concern that if castor were widely cultivated, it could contaminate nearby fields. Since most major crops in the US are resistant to the herbicide glyphosate, we evaluated the susceptibility of 5 week and 9 week old castor plants to the herbicide at levels appropriate to herbicide resistant plants. The younger plants are more susceptible to the herbicide, with half of the plants necrotic or entirely defoliated. More importantly, all the inflorescences were dead after one spray treatment. The 9 week old plants were much more resistant to the effects of the herbicide and required two spray treatments 4 weeks apart. This treatment resulted in significant defoliation but only 15% of the plants appeared necrotic or entirely defoliated. Of 148 inflorescences, 5 bore apparently normal seed pods. However, many of the seeds in the pods were well below normal in mass and oil content. Of 112 of these seeds planted, only two germinated, compared to the usual germination rate of >90% for castor seed. Thus, glyphosate treatment even on maturing castor plants can be an effective means for preventing volunteer castor plants.