First Report of Alder Yellows Phytoplasma Infecting Common and Grey Alder (Alnus glutinosa and A. incana) in Montenegro.

Abstract

Alder yellows phytoplasmas (AldYp) of the 16SrV-group associated with common alder (Alnus glutinosa) and grey alder (A. incana) are closely related to the grapevine yellows (GY)-associated quarantine phytoplasma Flavescence dorée (FDp). AldYp have been reported in several countries where epidemic appearance of FDp has been confirmed (France, Italy, and Serbia) (1,2). To date, the presence of 16SrV-group of phytoplasmas has not been reported in Montenegro; however, the main vector of FD phytoplasma, Scaphoideus titanus, has been identified in Montenegrin vineyards since 2008. During a survey in September 2011, in the northern part of Montenegro, 12 symptomatic alder trees showing symptoms of leaf discoloration, ranging from yellow to light green, were sampled. Six samples, each comprising several symptomatic leaves, were collected from A. glutinosa at streamside in woodlands near the town Kolašin and other six samples from A. incana close to the river Lim near the town of Bijelo Polje. Leaves of six young A. glutinosa seedlings were used as controls. Total DNA was extracted from fresh leaf midribs and petioles using the DNeasy Plant Mini Kit (Qiagen, Hilden, Germany). Nested PCR assay was conducted on 16S rRNA gene using phytoplasma generic primers P1/P7 and F2n/R2 followed by RFLP with MseI endonuclease (Fermentas, Vilnius, Lithuania) (3). Confirmation of identification and characterization of phytoplasma positive samples was performed by amplifying the non-ribosomal metionine aminopeptidase (map) gene using FD9f5/MAPr1 and FD9f6/MAPr2 primer set (1), specific for the members of the 16SrV group phytoplasmas. Amplification products were sequenced and deposited in GenBank (KC188998 through 9001). Comparison of the map gene sequences was performed by phylogenetic analysis along with 20 reference sequences of the 16SrV-group members (1), using the neighbor-joining method in MEGA5 software (4). 16S rRNA gene amplification revealed the presence of phytoplasmas in 11 out of 12 symptomatic samples, while Mse I restriction analysis and comparison with reference strains (AldYp and FDp from Serbia) enabled affiliation of detected phytoplasmas to the 16SrV-group. None of the controls were positive for any phytoplasma. Phylogenetic analysis of the Montenegrin AldYp map gene sequences revealed presence of four different strains clustering within the previously defined clusters of the 16SrV-group members (1). Three different strains associated with symptomatic A. glutinosa were identified and they clustered either within the FD1, FD2, or PGY-C cluster, while a single detected strain from A. incana proved to be identical with PGY-A isolate of AldY phytoplasma infecting grapevine in Germany (AM384892). To our knowledge, this is the first report of the association of 16SrV-group phytoplasmas with common and grey alder in Montenegro, as well as the first report of FD-related phytoplasmas in Montenegro. Since alder trees are considered as a possible natural reservoir of the FD phytoplasmas (1), the finding of alders naturally infected with strains related to the FDp (FD1 and FD2 clusters) indicate a possible threat of economic importance to the grape production in Montenegro, which should be addressed in further research.