Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: December 6, 2011
Publication Date: December 6, 2011
Citation: Zasada, I.A., Weiland, G.E., Reed, R.L., Stevens, J.F. 2011. Activity of meadowfoam (Limnanthes alba) seed meal glucolimnanthin degradation products against soilborne pathogens. Journal of Agricultural and Food Chemistry. 60:339-345. Interpretive Summary: Soilborne pathogens attack all crops of agricultural importance, causing billions of dollars in losses annually to U.S. farmers. One problem facing growers is the lack of safe and effective methods for controlling soilborne pathogen-induced crop losses. This makes the discovery of environmentally and economically sound control strategies critical. One potential control strategy is the incorporation of meadowfoam seed meal into soil. Meadowfoam is an oil seed crop grown in Oregon. After extraction of oil from seed, the remaining seed meal byproduct contains compounds that are potentially toxic to soilborne pathogens. Therefore, we tested five naturally-occurring compounds in meadowfoam seed meal against three soilborne pathogens. The study identified three meadowfoam seed meal compounds that were toxic and found that each pathogen differed in its sensitivity to these compounds. These results are significant because they identify specific compounds that are responsible for the toxicity of meadowfoam seed meal to soilborne pathogens. This research will be used by scientists developing the use of meadowfoam seed meal for reducing soilborne pathogen numbers in agricultural fields.
Technical Abstract: Meadowfoam (Limnanthes alba L.) is a herbaceous winter-spring annual grown as a commercial oilseed crop. The meal remaining after oil extraction from the seed contains up to 4% of the glucosinolate glucolimnanthin. Degradation of glucolimnanthin yields toxic breakdown products, and therefore the meal may have potential in the management of soilborne pathogens. To maximize the pest-suppressive potential of meadowfoam seed meal, it would be beneficial to know the toxicity of individual glucolimnanthin degradation products against specific soilborne pathogens. Meloidogyne hapla second-stage juveniles (J2) and Pythium irregulare and Verticillium dahliae mycelial cultures were exposed to glucolimnanthin as well as its degradation products. Glucolimnanthin and its degradation product, 2-(3-methoxyphenyl)acetamide, were not toxic to any of the soilborne pathogens at concentrations up to 1.0 mg/mL. Two other degradation products, 2-(3-methoxymethyl)ethanethioamide and 3-methoxyphenylacetonitrile, were toxic to M. hapla and P. irregulare but not V. dahliae. The predominant enzyme degradation product, 3-methoxybenzyl isothiocyanate, was the most toxic compound against all of the soilborne pathogens, with M. hapla being the most sensitive with EC50 values (0.0025 ± 0.0001 to 0.0027 ± 0.0001 mg/mL) 20-40 times lower than estimated EC50 mortality values generated for P. irregulare and V. dahliae (0.05 and 0.1 mg/mL, respectively). The potential exists to manipulate meadowfoam seed meal to promote the production of specific degradation products. The conversion of glucolimnanthin into its corresponding isothiocyanate should optimize the biopesticidal properties of meadowfoam seed meal against M. hapla, P. irregulare, and V. dahliae.