Characterization of Anti-Herbivore Property of Sicklepod Weed.

Among the wildlife species, deer, is responsible for 70% of soybean losses caused by wildlife, costing farmers more than $4.5 billion each year. Currently, the only effective and widely used technique to control deer in soybean fields are establishment of fences and application of repellents. Fencing is expensive and labor intensive to install. Effectiveness of repellents depends on numerous factors; rainfall may dissolve repellents, thus requiring reapplication, while some deer will ignore the odor and feed on repellents when extremely hungry. Plants possess varying levels of herbivore defense mechanisms, and weeds, because of their vast genetic and phenotypic diversity, are a good resource for anti-herbivore traits. Most studies on anti-herbivore mechanisms involve characterization of the compound or pathway responsible for herbivore defense; however, none of the studies have tried to test the activity and effectiveness of these anti-herbivore compounds or plant extracts and study its application in crop protection. In this study we prepared plant extracts of sicklepod and developed liquid formulation for application on soybean crop, and conduct HPLC analysis to identify the anti-herbivore compound. We tested the feed preference of sicklepod and soybean plants on four male deer. The deer consumed all soybean plants, but did not feed on any of the sicklepod plants, implying the potential anti-herbivore property in sicklepod. The anti-herbivory property of sicklepod is mainly associated with anthraquinone derivatives. The primary compounds identified in sicklepod leaves were chrysophanol (314 μg/g) and emodin (90 μg/g), and may therefore be responsible for the antiherbivory property of sicklepod. The anti-herbivore properties can be extracted from sicklepod and applied on soybean plants to provide protection against deer and other wildlife herbivores. Moreover, understanding the biochemical pathway or genes associated with the production of these anti-herbivore compounds can enable us to select or breed this trait into soybean.