Project Number: 1275-22000-251-02
Project Type: Specific Cooperative Agreement

Start Date: Sep 30, 2003
End Date: Sep 29, 2008

Objective:
Characterize the genetic diversity present in accessions of Xanthomonas axonopodis pv. citri, the citrus canker pathogen, in herbarium specimens collected by/for ARS over the past century in the USA and foreign countries. Implement real time quantitative PCR detection for contemporary strains of the pathogen.

Approach:
ARS maintains an herbarium collection of specimens of citrus canker infected plant material, including 'type' specimens. This material includes specimens from the 1914 outbreak in the USA as well as specimens from the same period collected throughout Asia. Samples from a total of 36 countries are represented in the collection, which is complemented by a similar contemporary collection of viable bacteria. Although the bacteria are no longer viable, methods of forensic PCR will be used to clone, sequence and compare the diversity present in this collection with the contemporary collection. The full genome sequence of a contemporary isolate is available to assist in primer design, and similar work has been described for Phytophthora infestans, which will provide the basis for technical methods and approach. Quantitative, real-time PCR will be developed based on well characterized and ARS-patented methods, using the LightCycler system.