Document Type

Thesis - Open Access

Award Date


Degree Name

Master of Science (MS)

Department / School

Agronomy, Horticulture, and Plant Science

First Advisor

Adam J. Varenhorst


Soybean aphids have been a significant pest of soybeans in North America since 2000. Before 2000, soybeans did not face significant insect pest pressure from any arthropods with piercing-sucking mouthparts. It is estimated that economic damage from soybean aphids range from $1billion to $4.7 billion annually. Research efforts focused on the identification of host plant resistance genes in soybean and discovered many resistant to Aphis glycines genes (i.e., Rag genes) in soybean. However, the adoption of commercially released Rag soybean cultivars has been limited. The prospect of management with Rag genes was further complicated by the identification of three virulent soybean aphid biotypes. Currently, biotype 4 is the greatest threat to management using Rag genes because it can colonize soybean containing Rag1, Rag2, Rag1+Rag2 or Rag1+Rag2+Rag4 genes. Previous studies have determined that soybean aphids illicit an induced susceptibility response in soybean. For example, virulent soybean aphid biotypes can obviate the resistance provided by Rag genes thereby allowing for the colonization by otherwise avirulent biotypes. This phenomenon was initially documented for biotype 1 and biotype 2 but not for biotype 4. In the first study we examined biotype 4 on Rag genes and found induced susceptibility. We then performed a second study that was an induced susceptibility screen using three plant introductions of soja with identified soybean aphid host plant resistance. We determined that induced susceptibility occurs on soja as well.

Library of Congress Subject Headings

Soybean -- Diseases and pests.
Soybean -- Disease and pest resistance.
Disease susceptibility.
Host plants.



Number of Pages



South Dakota State University



Rights Statement

In Copyright