The Allelopathic Effects of Palmer Amaranth (Amaranthus palmeri) on the Growth of Soil Fungal Pathogens.

Kayla L. Broster, Joseph L. Matthews, Karla L. Gage, Arjun Subedi, and Ahmad M. Fakhoury

Department of Plant, Soil, and Agricultural Systems

The allelopathic effects of Palmer amaranth (Amaranthus palmeri) on growth of soil fungal pathogens

Abstract

Weeds, such as Palmer amaranth, left uncontrolled in agricultural fields can result in crop yield loss. Aside from direct competition with crops, Palmer amaranth produces allelopathic compounds, or biochemical products that interfere with plant and microbe growth, and the effects have been noted on the growth of multiple crops; however, to our knowledge, effects on soil microbes have not been explored. The fungi tested, Fusarium viguliformae, F. graminearum, Macrophomina phaselina, Pythium ultimum, and Rhizoctonia solani, all have an economic impact on corn and soybean production. The objective of these experiments was to determine the allelopathic effects of Palmer amaranth residue on growth of fungal pathogens. Ground Palmer amaranth residue was added to potato dextrose agar (PDA) or broth (PDB), and accessions of each fungal pathogen were introduced to the media preparations. PDA- and PDB-alone were used as controls. Radial growth of fungi was assessed by inoculating petri plates of PDA with 6 mm plugs cultured from each fungus. Radial growth was measured twice daily for 7 days, while incubating plates at room temperature. Fungal biomass growth was assessed by inoculating flasks of PDB with 6 mm plugs of M. phaseolina, P. ultimum, and R. solani. Flasks were incubated, collected, and dried after 7 days. Results indicate that there is an interaction between Palmer amaranth residue and growth of some fungal species. Radial growth of P. ultimum was most sensitive to Palmer amaranth residue with an increase in radial growth. M. phasolina and P. ultimum biomass increased with Palmer amaranth residue but did not differ between treatment and control for R. solani. Accelerated growth may indicate the fungus is attempting to overcome stress caused by the allelopathic compounds. More research is needed, but increased fungal growth may result in disease spread, underscoring the need for integrated weed and fungal pathogen controls.