APS 2009 Annual Meeting Abstract of Presentation

A diagnostic real-time PCR assay for the detection and quantification of Xanthomonas axonopodis pv. phaseoli and X. axonopodis pv. phaseoli var. fuscans
Y. HE (1), A. Fessehaie (1), L. Shepherd (1), G. Munkvold (1)
(1) Seed Science Center, Iowa State University, Ames, IA, USA
Phytopathology 99:S34

Common bacterial blight of bean is caused by Xanthomonas axonopodis pv. phaseoli (Xap) and Xanthomonas axonopodis pv. phaseoli var. fuscans (Xapf). These seedborne, quarantined pathogens can cause up to 40% yield loss in susceptible cultivars and also reduce seed quality, especially if seed is produced under humid conditions. Seed health testing is one of the most significant control steps to protect against contamination of seeds for domestic planting and international seed trade. Based on sequence information from RAPD fragments generated by Xap-specific primers, we developed a real-time PCR for detection and quantification of Xap and Xapf. Primer and probe specificity was tested against DNA of several Xanthomonas species and pathovars of X. axonopodis. Several close related Xanthomonas strains could not be amplified using this PCR assay. The detection limit of the TaqMan assay for purified DNA and cells was 20 fg and 20 CFU per 25 µl PCR reaction mixture, respectively. This assay may be useful as a rapid, highly sensitive and specific detection method to ensure seed quality control and meet phytosanitary regulations. This is also the first real-time PCR assay developed for Xap and Xapf.