Characterization and Deer-Repellent Property of Chrysophanol and Emodin from Sicklepod Weed

Deer, particularly white-tailed deer (Odocoileus virginianus), damage row crops such as soybean (Glycine max L.) and are a perceived problem in the continental US. Currently, the only widely used technique to control deer from crop browsing is establishment of fences, which is expensive, labor intensive, and most of the time ineffective. Studies have shown that sicklepod, Senna obtusifolia (L.), contains anthraquinone derivatives, which in separate studies were shown to be toxic to cattle, rats, rabbits, and horses, and repel herbivores primarily birds. However, information of the deer-repelling property of anthraquinone in sicklepod is lacking. Field tests conducted at our Captive Deer Facility at MississippiStateUniversity(MSU) confirmed the deer-repelling property of anthraquinone extracts from sicklepod. Soybean plants applied with control treatment (water) were browsed by deer, while plants applied with sicklepod anthraquinone extracts were avoided. Using chromatography techniques, we found the levels of anthraquinone derivatives (chrysophanol, emodin) in sicklepod plant parts in the order: root > fruit > stem/leaf. Hydrolysis of water extracts of sicklepod seed produced high emodin concentration, suggesting emodin glycoside as the main form of anthraquinone glycoside in sicklepod seed. Deer-repelling compounds can be extracted in its pure form from sicklepod and applied on soybean to increase its repelling efficacy on deer, and at the same time protect soybean yields.

Phenotyping of Weedy Rice to Assess Root Characteristics Associated with Allelopathy

Weedy rice is a species of Oryza, and is a wild relative of cultivated rice. The weed possesses unique hardiness that allows them to thrive in dynamic and stressful environments. These characteristics suggest that weedy rice is a stored source of novel genes for competitive traits. One such trait is allelopathy, where a species releases secondary metabolites that suppress the growth and development of neighboring species. Weed competition is a limiting factor in rice production systems;therefore, it is critical to identify specific allelopathic weedy rice accessions to determine the genetic pathways and mechanisms associated with allelopathy to be used in breeding programs. Due to the complex nature of allelochemical production and the lack of knowledge of allelopathy mechanisms in weedy rice, phenotypic traits, particularly root traits, can be used to overcome this limitation and serve as target characteristics for breeding weed suppressive rice varieties. Five weedy rice accessions were chosen from preliminary screenings of larger sample sizes with the ability to suppress barnyardgrass weed seedling growth. Another five weedy rice with low barnyardgrass suppression was selected for the current root phenotypic study. Five cultivated rice lines were used as a comparison. All plants were propagated in a transparent germination pouch for four weeks. Roots were scanned and analyzed for root length and area covered. No differences were found in the seedling root area among weedy rice and rice accessions;however, allelopathic weedy rice plants exhibited a 14% increase in root length than non-allelopathic weedy rice plants. The allelopathic weedy rice accession B2 possessed the most extended root system (22.4 cm root length). The highly allelopathic weedy rice accessions (including B2) screened and phenotyped in this study are ideal candidates for identifying the genetic controls of early root length, a possible trait contributing to underground allelopathic production and competitive advantage.