Abstract

Plant-parasitic nematodes account for 14% crop loss globally and $157 billion loss annually. Root-knot nematodes are yield-limiting and threaten crop production. Toxic chemicals, such as oxamyl, found in industry-standard nematicides can kill helpful microbes and present environmental threats. Previous research identified alpha-terthienyl, a pigment in marigolds, with nematicidal properties. The objective of this investigation was to evaluate marigolds as an herbal bio-nematicide to control nematodes compared to industry-standard, Vydate. 100 marigold plants were planted and root, stem, and flowers were dried and used to generate extracts by performing steam distillation. Nematodes were extracted from soil culture for in vitro assay and used for 5 treatments (untreated control, flower, root, stem extract, industry-standard) replicated 10 times. Nematode counts were taken 5 times over 96-hours. 30 tomato plants were used in vivo to determine the effectiveness of treatments against root galling. After 3 weeks of inoculating nematodes, root galling was observed. In the in-vitro study, root extract had the highest average decrease in nematode count (87.4%) compared to flower (85.2%) and stem (60.8%) extracts after 96 hours. In comparison, industry-standard had a reduction of 100%. Paired t-tests also show root extracts as having the lowest p-value (1.31x10^-9) after industry-standard, conveying greater statistical significance.  As per the root galling data, marigold extracts had 20.0% less galling compared to untreated control after 3 weeks. In conclusion, the plant extracts were effective in nematode management in vitro, indicating there is significant potential for marigold extracts to be commercially developed.