MOLECULAR INTERACTION BETWEEN THE RUSSIAN WHEAT APHID

AND WHEAT HOSTS

Nora Lapitan^1*, Youchun Li¹, and Anna-Maria Botha-Oberhoster^1,2

Department of Soil and Crop Sciences, Colorado State University,

Fort Collins CO 80523¹; Cereal Genomics, Department of Genetics and FABI, University of Pretoria, Hillcrest Pretoria ZA0002 South Africa².

*Corresponding Author: PH ((70) 491-1921; e-mail: nlapitan@lamar.colostate.edu

ABSTRACT

The Russian wheat aphid (RWA) was first discovered in North America in 1986 and quickly became the most important insect pest of wheat in the western United States. Between 1986 and 2003, RWA infestations have caused a total economic impact approaching $1 billion, including the use of nearly 20 million pounds of insecticides. The use of resistant cultivars has been the most effective means to control RWA. During the last two years however, several new biotypes were discovered in the western great plains that overwhelmed existing resistance genes in wheat. Little is known about the genetics of the RWA and the basis for rapid development of new biotypes. Furthermore, the interaction between RWA and wheat is poorly understood. Understanding the genetic basis of RWA biotype evolution and its interaction with wheat can open up new possibilities in developing novel strategies to control RWA. The long-term goals of this research are 1) to elucidate the molecular interaction between the RWA and wheat, and 2) to understand the genetic basis of the rapid evolution of RWA biotypes. Polymorphisms in SSR patterns were observed among five U.S. biotypes. Development of DNA fingerprints for the different biotypes are underway. These DNA fingerprints will be useful for studying the distribution of biotypes within the US., their genetic relationships, and genetic basis of biotype development. An in vivo assay was developed to identify the aphid elicitor, that is, the chemical component from the aphid that induces susceptible symptoms in plants. When buffer containing ground aphids were injected into wheat, susceptible genotypes exhibited leaf rolling, a typical susceptible symptom following aphid feeding. Resistant genotypes injected with the same extract, as well as plants injected with buffer only, did not show leaf rolling. Aphid fractions containing proteins or metabolites were injected into resistant and susceptible genotypes to narrow down the chemical component of aphid elicitors. The biochemical response of wheat plants injected with these different components were also investigated. The results indicate that the aphid elicitor(s) consists of proteins. A working model for the interaction between the RWA and wheat will be presented.