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United States Department of Agriculture

Agricultural Research Service

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Location: Genetic Improvement for Fruits & Vegetables Laboratory

2013 Annual Report

1a. Objectives (from AD-416):
Objective 1: Identify genes involved in pathogenicity/virulence of Phytophthora infestans and Streptomyces scabies. Objective 2: Identify variations in genome sequences that distinguish isolates of Phytophthora infestans and Streptomyces scabies. Objective 3: Develop transgenic potato and tomato plants for functional genomics and disease resistance application.

1b. Approach (from AD-416):
Characterization of pathogen isolates will be followed by defined, reproducible studies on interactions with a specific host using these isolates. Genes potentially involved in pathogenicity for each pathogen will be sought using a bioinformatics approach to select and screen candidate genes from the respective genome databases for each pathogen. Testing these genes will be carried out using methods of over-expression and suppression. Multiple databases of genetic information available for Solanaceous crop plants (potato, tomato, eggplant, pepper) will be used to help select genes that may be involved in limiting disease caused by Phytophthora and Streptomyces. Once candidate genes are identified, their role in limiting disease will be determined. Simultaneous studies of pathogen and host will provide new information and tools to be used in breeding and engineered control strategies to limit these major diseases of potato and tomato.

3. Progress Report:
Three endoglucanase genes have been identified, cloned and placed into a transformation vector for use in gene disruption studies with S. scabies. Genomes from two isolates of S. scabies have been sequenced. Genome comparisons are underway to investigate genetic differences. Potato transformation has become standardized, and we now have the capacity to transform numerous different cultivars and germplasm lines.

4. Accomplishments
1. Variation in plant pathogen isolates can result in misdiagnosis of disease resistance in crop plants. Over one thousand isolates of the bacterial pathogen that causes a potato disease called common scab have been characterized and made available for disease screening. This collection allows potato breeders to screen their experimental breeding lines and cultivars against a broad spectrum of isolates, allowing for a more accurate assessment of disease resistance.

2. Cell wall development plays a vital role in plant growth. Defense against disease causing microbes is also mediated through modifications to the plant cell wall. A protein believed to play a role in deactivating a pathogen cell wall degrading enzyme was shown to have a unique, previously unidentified role in plant cell wall development. Transgenic plants expressing this protein produce potato tubers with a shape like the wild potatoes (thin, knotted, twisted shape) that were the progenitors to modern cultivated potato (smooth, round or oblong). Inadvertent selection against this protein by potato breeders may be the basis for modern potato shape. Identifying and controlling this protein may allow for new shapes and sizes of potato tuber.

Review Publications
Jones, R.W. 2012. Multiple copies of genes encoding XEGIPs and EDGPs are harbored in an 85kB region of potato genome(Solanum tuberosum). Plant Molecular Biology Reporter. 30:1040-1046.

Jones, R.W., Perez, F.G. 2012. First report of Colletotrichum acutatum on tamarillo in the United States. Plant Disease. 96:587.

Dees, M.W., Wanner, L.A. 2012. In search of better management of potato common scab. Potato Research. 55:249-268.

Last Modified: 2/23/2016
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