2008 Annual Report
We have completed a large experiment that identified many genes that are important for wheat plant resistance against the Hessian fly. The data are currently being analyzed, but we have begun to verify the results and find that the data are very reliable so far. We are about to do a second experiment that will target additional genes that could not be analyzed with the methods used in the first experiment.
Analysis of genes expressed in Hessian fly larvae associated with larval attack and damage of wheat has been initiated. Of particular interest is gene expression in larvae on resistant wheat where a lesion forms in the plant’s tissue containing dead larvae versus resistant wheat where no lesion forms. Analyses by electron microscopy of the midgut of young larvae on resistant wheat indicates the lining of the midgut is disrupted and sloughing off, while in larvae on susceptible wheat the midgut lining has a normal appearance. These results suggest the midgut may be a target for toxic compounds produced in resistant wheat. A comparative study of genes expressed in young larvae from an Israeli Hessian fly population with those from populations in the United States also has been initiated. This study is of interest because the Hessian fly from Israel shows virulence to a wider range of genes for resistance in wheat than populations in the United States. It is anticipated a comparative study of genes expressed between Israeli populations and populations in the United States will reveal genes important in the ability of Hessian fly larvae to attack and damage wheat.
We have used two and three base pair repeating genetic markers, known as microsatellites to look at populations of Hessian fly from the Southeastern United States. The studies have revealed significant differences between populations of Hessian fly, but the differences between populations do not appear to be related to distance, but rather with ecological differences in climate. These studies have also shown a large amount of genetic variation within these populations, in spite of increased pressures by deployment of resistant wheat. This work allows us to gain better insight on the evolution of the host/pest genotypic interaction and better predict new risk management strategies.
Our objectives and milestones address Component 3 (Genetic Improvement of Crops) Problem Statement 3C (Germplasm Enhancement/Release of Improved Genetic Resources and Varieties) of the Action Plan for NP 301 (Plant Genetic Resources, Genomics and Genetic Improvement). Progress to date is providing basic knowledge to enhance native resistance in wheat to Hessian fly, enable future transgenic approaches to resistance, and provide an understanding of the evolution of virulent pest genotypes and risk management for deployment of host resistance.
Testing Gene flow between neighboring Hessian fly populations.
Knowledge of gene flow between Hessian fly populations is currently unknown, and such knowledge is essential to understanding the spread of virulence through populations. To provide microsatellite markers to assess gene flow between neighboring populations and to further knowledge of the recombination and mutation rates at points of interest in the pest’s genome we have physically mapped on salivary polytene chromosomes microsatellites to be used in population analyses. These microsatellite markers will allow us to address questions of ancestral relatedness between populations and gene flow as issues for an effective control program. Results will have a direct impact on the ability to assess the spread of virulence through Hessian fly populations in the United States. This accomplishment addresses Component 3 (Genetic Improvement of Crops) Problem Statement 3C (Germplasm Enhancement/Release of Improved Genetic Resources and Varieties) of the current Action Plan for National Program 301 (Plant Genetic Resources, Genomics and Genetic Improvement).
Identifying virulence factors in Hessian fly affecting its ability to attack wheat.
The most effective control for Hessian fly is resistant wheat; however, the deployment of resistance has led to the development of more virulent genotypes of the pest. We are identifying virulence factors within the pest that affect its ability to attack wheat. Through this research we identified a gene that codes for a secreted lipase-like protein in the salivary glands of the larval Hessian fly. We have shown the protein is likely secreted into host-plant cells during feeding and has a role in the establishment of the larval feeding site. Results have a direct impact on future genetically engineered resistance to compliment native resistance in wheat. This accomplishment addresses Component 3 (Genetic Improvement of Crops) Problem Statement 3C (Germplasm Enhancement/Release of Improved Genetic Resources and Varieties) of the current Action Plan for National Program 301 (Plant Genetic Resources, Genomics and Genetic Improvement).
Wheat genes responding to Hessian fly infestation.
Hessian flies pose a continuing threat to wheat production so we are studying genes with potential use in improving resistance to understand their mode of action. A wheat lectin that may deter larval feeding is able to bind high-mannose glycoproteins, such as those found in larval digestive organs. Information about genes involved in resistance will pinpoint mechanisms that can be manipulated in future crop protection strategies that employ transgenic resistance. This accomplishment addresses Component 3 (Genetic Improvement of Crops) Problem Statement 3C (Germplasm Enhancement/Release of Improved Genetic Resources and Varieties) of the current Action Plan for National Program 301 (Plant Genetic Resources, Genomics and Genetic Improvement).
5.Significant Activities that Support Special Target Populations
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Shukle, R.H., Yoshiyama, M., Morton, P.K., Schemerhorn, B.J. 2007. Tissue and developmental expression of a gene from Hessian fly encoding an ABC-active-transporter protein during interactions with wheat. Journal of Insect Physiology. 55:146-154.