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Funded Project

Funding Program: Regional IPM Grants (S-RIPM)

Project Title: Using DNA Diagnostics to Predict Potentially Damaging Isolates of Greenbug

Project Director (PD): Keyan Zhu-Salzman [1]

Lead State: TX Lead Organization: Texas A&M University

Research Funding: $39,767

Start Date: Jun-15-2004 End Date: Dec-31-2006

Pests Involved: greenbug

Summary: The greenbug, Schizaphis graminum (Rondani), infests more than 70 cultivated and wild grass hosts. This aphid causes annual losses of $126 million to sorghum, Sorghum bicolor (L.) Moench and $240 million to wheat, Triticum aestivum L., in the Southern Great Plains, of the United States. Use of resistant cultivars is the major IPM strategy for managing greenbugs. However, new resistance-breaking biotypes have been discovered two to five years after release of every resistant sorghum. Without mating, female greenbugs give birth to living young. Because new greenbug biotypes that can damage sorghum have been identified in such rapid succession, populations with great genetic diversity probably exist in nature. No method exists to predict new damaging biotypes. Being able to predict future predominant greenbug biotypes is imperative to breeding resistant sorghum, thus avoiding devastating outbreaks. Despite no apparent morphological differences, variation in genetic information among greenbug populations can be detected by using molecular techniques. Amplified fragment length polymorphism (AFLP) allows genomewide identification of molecular markers from little DNA and is highly repeatable. When AFLP was used for distinguishing eight greenbug biotypes, biotypes able to damage sorghum in the field shared more common polymorphic markers among themselves than with non-sorghum biotypes, suggesting that a common genetic factor(s) responsible for fitness on sorghum might be shared by sorghum greenbug biotypes. These markers would be useful for monitoring new biotypes. The goal of this research is to use a high-throughput DNA diagnostic method to identify greenbugs with the potential to become pests of sorghum. Greenbugs will be collected and biotyped from cultivated and wild grass hosts. AFLP markers will be used to analyze the DNA and differentiate among the greenbug isolates from the field. Greenbugs with great similarity to known sorghum biotypes will be evaluated for ability to damage resistant sorghums. This information will be provided to extension agents and specialists to provide to farmers and to sorghum breeders who are developing resistant sorghums for release to the commercial seed industry. Thus, greenbugs could be managed before outbreaks occur and sorghum yield would be maintained by an environmentally friendly approach. Objectives: The greenbug aphid, Schizaphis graminum (Rondani), causes annual loss of hundreds of millions of dollars on sorghum, Sorghum bicolor (L.) Moench, wheat, Triticum aestivum L., and other small grains in the Southern Great Plains of the United States. Use of resistant cultivars is hindered by outbreaks of new greenbug biotypes that are insensitive to resistance factors. To date, no method exists to predict new biotypes that could damage sorghum or wheat. New biotypes are identified only after resistant cultivars become dysfunctional in managing greenbugs. Being able to predict future dominant greenbug biotypes is imperative to breeding resistant crops, thus preventing devastating outbreaks of greenbugs. This proposal is to use high-throughput DNA diagnostic method to identify greenbugs that have potential to become future new biotypes. The specific objectives of this research are to: (1) Determine the number and distribution of greenbug biotypes by obtaining and culturing greenbugs from major sorghum-growing counties in Texas and neighboring states. (2) Use AFLP technique to identify greenbug isolates that have 0.9 or greater similarity coefficients with any known sorghum-feeding biotype. (3) Test greenbug isolates that have 0.9 or greater similarity coefficients with sorghum biotype for ability to live on and damage resistant sorghum lines currently available. Results will allow us, for the first time, to predict which greenbug isolates have the greatest potential to damage sorghum before outbreaks occur.

Final Report:

Results The greenbug aphid, Schizaphis graminum (Rondani) causes annual losses of $126 million to sorghum and $240 million to wheat the United States. Use of resistant cultivars is the major IPM strategy for managing greenbugs. However, new resistance-breaking biotypes have been discovered two to five years after release of every resistant sorghum. We collected and cultured greenbugs from sorghum-growing counties in Texas and use both bioassay and molecular techniques to biotype the greenbug isolates. All isolates cultured are diagnosed as biotype I. The reason for the lack of detection of potential new biotypes could be due to the limit of the collecting region (major sorghum-growing counties in Texas). Broader range of sample collection may lead to identification and isolation of new biotypes. IMPACT: 2004/06 TO 2006/12 The work provided information to extension agents and sorghum breeders on the currently existing and most abundant greenbug biotypes in Texas sorghum-growing counties. Continuous monitoring changes in greenbug population will help breeders developing resistant sorghum lines before outbreaks occur. Use of resistant cultivars is an environmentally friendly approach for pest management. PUBLICATIONS (not previously reported): 2004/06 TO 2006/12 No publications reported this period

Outcomes N/A

Impacts From report submitted by the PI to USDA CRIS report system The work provided information to extension agents and sorghum breeders on the currently existing and most abundant greenbug biotypes in Texas sorghum-growing counties. Continuous monitoring changes in greenbug population will help breeders developing resistant sorghum lines before outbreaks occur. Use of resistant cultivars is an environmentally friendly approach for pest management.

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