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Castilleja coccinea, commonly known as Scarlet Indian Paintbrush, is a root hemiparasitic plant native to Illinois and other areas of the central and eastern United States. As a hemiparasite, C. coccinea is green and photosynthetic, but grows haustoria that penetrate neighboring plants’ roots to steal various types of nutrients. Castilleja coccinea can survive alone, however, it is not known to fully mature without having penetrated roots of a host plant. Castilleja coccinea is known to parasitize many vascular plant species, and scant literature suggests Lobelia spicata, commonly known as Pale Spiked Lobelia, is a viable host. Lobelia spicata is also native to Illinois prairies and other surrounding areas of the United States. We tested the hypothesis that by taking minerals, water and other nutrients from the host’s xylem stream, C. coccinea reduces host growth and alters the host’s allocation to shoot and root growth, and that L. spicata would be a suitable host for this particular hemiparasite. Castilleja coccinea seeds were added to young L. spicata plantlets and fertilized with either high or low concentration of fertilizer. Plants were harvested, cleaned, dried and weighed approximately 31 weeks after the addition of C. coccinea seeds, and the masses of roots and shoots were recorded and compared. Parasitism by C. coccinea significantly reduced root and especially shoot growth of the host, but the impact was dependent on the level of fertilizer. Shoot mass of L. spicata was depressed regardless of fertilizer level, but root mass was significantly reduced only in L. spicata treated with [high] fertilizer. We conclude that: (1) Lobelia spicata is a viable host for Castilleja coccinea, (2) this hemiparasite strongly reduces growth of the host, but (3) the impact of the hemiparasite on host growth depends on nutrient supply. Currently, little information about C. coccinea’s preferred hosts and their dynamic relationships is available, so these results add to the understanding of hemiparasite-host interactions.
Edmondson, Jessica, "Parasite Packs a Punch: Impact of Scarlet Indian Paintbrush on the Growth of its Host" (2020). Biological Sciences. 4.
Authors: Jessica Edmondson, Victoria Borowicz
This project has not received IRB approval.