Amultiplex-PCR assayforidentificationofthe quarantine plantpathogen Xanthomonas axonopodis pv. phaseoli

article i nfo In this study we developed an algorithm to screen for all exact molecular signatures of the quarantinepath- ogen Xanthomonas axonopodispv. phaseoli (Xap), based on available data of the presence or absence of virulence-associated genes. The simultaneous presence of genes avrBsT and xopL is specifi ct oXap. Therefore we developed a multiplexPCR assaytargeting avrBsT and xopL for the molecular identification of Xap. The specificity of this multiplexwas validated by comparison to that of other molecular identification assaysaimed at Xap, on a wide collection of reference strains. This multiplexwas further validated on a blind collec- tion of Xanthomonasisolates for which pathogenicity was assayedby stem wounding and by dipping leaves into calibrated inocula. This multiplexwas combined to the previously described X4c/X4e molecular identi- fication assayfor Xap. Such a combination enables the molecular identification of all strains of Xanthomonaspathogenic on bean. Results also show that assayby stem wounding does not give reliable results in the case of Xap, and that pathogenicity assaysby dipping should be preferred.