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Development, Comparison, and Validation of Real-Time and Conventional PCR Tools for the Detection of the Fungal Pathogens Causing Brown Spot and Red Band Needle Blights of Pine

First, third, and fourth authors: Laboratoire National de la Protection des Végétaux, Station de mycologie, IFR 110, Domaine de Pixérécourt, F-54220 Malzéville, France; and second, fifth, and sixth authors: INRA, Nancy-Université, UMR1136 Interactions Arbres-Micro-organismes, IFR 110, F-54280 Champenoux, France.

Dothistroma pini, D. septosporum, and Lecanosticta acicola are fungal pathogens that cause severe foliage diseases in conifers. All three pathogens are listed as quarantine organisms in numerous countries throughout the world and, thus, are subject to specific monitoring. Detection and identification of these pathogens still often relies on cumbersome and unsatisfactory methods that are based upon the morphological characterization of fungal fruiting bodies and conidia. In this study, we present the development of several new molecular tools that enable a rapid and specific in planta detection of each of these pathogens. Several DNA extraction procedures starting from infected needles were compared and four commercial DNA extraction kits provided DNA of satisfactory quality for amplification by polymerase chain reaction (PCR). In addition, we developed several sets of conventional PCR primers, dual-labeled probes (DLPs), and duplex-scorpion probes (DSPs), all of which targeted each pathogen. Their ability to detect the pathogens in a series of naturally infected needle samples was compared. The quadruplex DLP real-time assay proved to be more sensitive than the DSP assay and conventional PCR but the two real-time probe formats yielded identical results in the naturally infected samples. Both real-time assays proved to be significantly superior to the technique of humid chamber incubation, which often failed to produce spores for the accurate identification of the pathogens.