Abstract
In this work, we rechecked, using species-specific Loop mediated isothermal AMPlification (LAMP) diagnostic assays followed by sequencing of fungal isolates at the beta-2-tubulin (tub2) gene region, a historical and never confirmed report of Dothistroma needle blight (DNB) in the introduced Monterey pine (Pinus radiata D. Don) in the mountains in the extreme tip of southern Italy. The report dates back to the mid-1970s, and predates the molecular-based taxonomic revision of the genus Dothistroma that defined the species accepted today. In the fall of 2019, symptomatic needles of Monterey pine and Corsican pine (Pinus nigra subsp. laricio (Poir.) Palib. ex Maire) were sampled in the area of the first finding. The applied diagnostic methods revealed the presence of Dothistroma septosporum (Dorogin) M. Morelet on both pine species. In this way, we: (i) confirmed the presence of the disease; (ii) clarified the taxonomic identity of the causal agent now occurring at that site; (iii) validated the species-specific LAMP diagnostic protocol we recently developed for Dothistroma for use on a portable field instrument, and (iv) showed that the pathogen now also attacks the native P. nigra subsp. laricio, a species particularly susceptible to the disease, indigenous to the mountains of Calabria, which is one of the very few areas where the species’ genetic resources are conserved. Comparative genetic analysis of the rare populations of D. septosporum found in the central Mediterranean region and in the native range of P. nigra subsp. laricio could help to clarify the history of the spread of the pathogen in southern Europe and better evaluate the risk it poses to the conservation of native pine species.
Highlights
Typical Dothistroma needle blight (DNB) symptoms were present on all needle samples taken in six different groups of pines, two of P. radiata and four of P. nigra subsp. laricio, on the south-facing slopes towards Lake Metramo at elevations ranging from about 900 to 1100 m a.s.l
In confirming the persistence of the pathogen in the area, we demonstrated that the recently published Loop mediated isothermal AMPlification (LAMP) diagnostic assays discriminating the infections by DNB agents and
Application of LAMP diagnostics and sequencing in the tub2 gene region confirmed the pathogen found today in the study area to be the species currently identified as D. septosporum
Summary
Dothistroma needle blight (DNB) is a serious foliar disease of pines with a worldwide distribution [1,2]. Causal agents of the disease are two closely related ascomycete fungi, Dothistroma septosporum (Dorog.) Morelet Scirrhia pini Funk & Parker, teleomorph: Mycosphaerella pini Rostr.), and Dothistroma pini Hullbary (teleomorph:unknown) [3]. These pathogens induce quite similar symptoms consisting initially of water-soaked lesions that later develop into small brown-to-reddish spots. Within these spots, black conidiomata differentiate under favorable conditions. Spots later expand to the whole needle circumference, resulting in transverse bands, the alternative name “red band needle blight”
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