Ayanna D. Montegut

The Responses of Susceptible and Resistant Amaranthus palmeri (Palmer Amaranth) to Acetic Acid as an Organic Herbicide Treatment

Ayanna D. Montegut, Ineceia I. Carter, and Yolander Youngblood (Faculty Mentor)

Department of Biology, Prairie View A&M University

Traditional herbicides are glyphosate-based. Overuse of these herbicides has led to glyphosate resistance in some plants. Amaranthus palmeri is one of them. This is an ongoing study whereby we investigate the responses of the Glyphosate-Susceptible and the Glyphosate-Resistant Amaranthus palmeri to acetic acid as an organic herbicide. We hypothesized that although both forms respond differently to glyphosate-based herbicides, both respond the same to organic-based herbicides. When both are treated in a greenhouse with an organic 10% acetic acid solution, they both die. A 10% acetic acid solution was used versus the standard 20% acetic acid solution because previous studies suggest that at a very young age, the 10% solution is strong enough to control the growth. Using a weaker solution is less costly to the farmers' pocket and to the environment. We treated young Glyphosate-Susceptible and Glyphosate-Resistant Amaranthus palmeri plants by spraying the leaves with a 10% acetic acid solution. We observed changes in the epidermal layer. These plants are C4 plants and have stomata on their adaxial and abaxial leaf surfaces. Most leaves have stomata only on their abaxial surfaces. When treated with 10% acetic acid plants start wilting process within two hours. Using the JEOL Scanning Electron Microscope (SEM) we took micrographs to show that leaf stomata are open before the leaves are treated. The micrographs also show that after treatment, as the plants become stressed, the stomata close on both forms. The leaf surfaces of both plants respond the same way. Death did occur with both plant forms. However, there was a slight difference in the death rate. With the Glyphosate Susceptible plants, 85% died within 24 hours, while with the Glyphosate-Resistant plants 100% died within 24 hours. Future computation studies will look at gene expression and address this difference in death rate.

Key words: Amaranthus palmeri, Glyphosate Susceptible, Glyphosate Resistant, organic acetic acid herbicides

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