CHARACTERISTICS OF A PCR-BASED ASSAY FOR IN PLANTA DETECTION OF XANTHOMONAS-CAMPESTRIS PV PELARGONII

Polymerase chain reaction (PCR) amplification was carried out with a p rimer pair targeting a sequence in the genome of Xanthomonas campestri s pv. pelargonii, the causative agent of bacterial blight in geraniums . PCR amplification with the primer pair XcpM1/XcpM2 using total nucle ic acid preparations from 22 geographically-diverse isolates of X. cam pestris pv. pelargonii generated a major 197 bp DNA product. In contra st, no major amplification products were consistently generated from 1 2 other pathovars of X. campestris or from 19 isolates representing 10 different plant pathogenic bacteria, including two other bacterial pa thogens of geraniums, Corynebacterium fascians and Pseudomonas cichori i. After PCR using this primer pair, between 1380 and 13 800 copies of the X. campestris pv. pelargonii bacterial DNA target as template wer e detected by ethidium bromide staining of agarose gels, and between 1 3.8 and 138 copies by blot hybridization to a pathovar-specific biotin ylated probe. Similarly, between 630 and 6300 colony-forming units (CF U) of X. campestris pv. pelargonii could be detected after ethidium br omide staining of agarose gels, and between 63 and 630 CFU after blot hybridization. The PCR-based assay was used to identify X. campestris pv. pelargonii in diseased geraniums; whereas discrete amplification p roducts were not obtained with healthy plants.