A PCR protocol for the identification of Pseudomonas syringae pv. tagetis based on genes required for tagetitoxin production

A polymerase chain reaction (PCR) protocol that can be used to distinguish Pseudomonas syringae pv. tagetis from other P. syringae pathovars, including those that induce apical chlorosis in several plants of the Asteracaea family and in pea, and closely related P. savastanoi pathovars was developed based on DNA sequences from P. syringae pv. tagetis that are required for tagetitoxin synthesis. PCR primer sets designated TAGTOX-9 and TAGTOX-10 in PCR amplifications with DNA from most strains of P. syringae pv. tagetis, produced amplicons of 507 and 733 bp, respectively. The same size amplicons were produced in PCR amplifications with bacterial cells isolated from chlorotic leaf tissue from Canada thistle (Cirsium arvense) plants infected with P. syringae pv. tagetis. Among 16 other P. syringae pathovars, only PCR amplifications with DNA from P. syringae pv. helianthi produced the same size amplicons with the respective primer sets. Low levels of the 507-bp amplicon were produced in PCR amplifications with the TAGTOX-9 primers and DNA from P. syringae pv. helianthi or the nontoxigenic strains of P. syringae pv. tagetis. These results suggest that P. syringae pv. helianthi, the most closely related pathovar to P. syringae pv. tagetis, may be a nontoxigenic form of P. syringae pv. tagetis. Results from PCR amplifications with the TAGTOX-9 and TAGTOX-10 primers provide strong evidence that the newly described Pseudomonas syringae pathovars, CT99B016C isolated from Canada thistle and PP105 and Pisum97-1 isolated from pea, which cause apical chlorosis in these respective hosts, are different from P. syringae pv. tagetis. Published by Elsevier Inc.