First report of alder yellows phytoplasma on common alder (Alnus glutinosa) in Serbia

Alder yellows (AldY) phytoplasma associated with common alder (Alnus glutinosa) and grey alder (A. incana) belongs to the 16SrV-C group and is closely related to the Flavescence dorée (FD) phytoplasma, a quarantine pathogen of economic importance that affects vineyards of southern Europe including Serbia. AldY phytoplasma has been reported in France, Germany, Switzerland, Austria, Italy and in the Baltic region (Arnaud et al., 2007) where alders are frequently infected, exhibiting symptoms such as yellowing, small leaves, reduced foliage, or sometimes infected trees remain symptomless (Lederer & Seemüller, 1991). During September 2007, leaves with petioles from twelve alder trees showing symptoms of discrete leaf yellowing (Fig. 1) and multiple shoot growth from the basal part of trunk, were collected from three different sites in the vicinity of Topola (Central Serbia) and another twelve samples showing discrete symptoms were collected from one site near Veliko GradiÅ¡te (East Serbia). Leaves of six asymptomatic young alder seedlings were used as controls.

Figure 1: Yellowing symptoms on common alder (Alnus glutinosa). The tree shown was positive for AldY phytoplasma.

DNA was extracted from fresh leaf midribs and petioles from affected and asymptomatic plants according to previously reported protocols (Angelini et al., 2001). Initial phytoplasma identification was conducted using a nested PCR assay with P1/P7 and 16r758f/M23Sr primers on the 16S rRNA gene, followed by RFLP analysis with TaqI restriction enzyme. RFLP profiles showed the presence of phytoplasmas of the 16SrV-C group in all symptomatic samples (Fig. 2). Further characterization was performed by amplifying the ribosomal protein gene operon using primers rp(V)F1/rpR1 followed by rp(V)F1A/rp(V)R1A, followed by digestion with MseI (Fig. 3) (Lee et al., 2004). Two different MseI RFLP profiles were detected among the AldY phytoplasma isolates: one similar to FD-C and one (only in samples from Eastern Serbia) similar to the AldY strain previously described by Lee et al. (2004). None of the asymptomatic plants were positive for the presence of phytoplasma.

This is the first report of phytoplasmas associated with common alder in Serbia and of the association of two distinct isolates belonging to rRNA group 16SrV-C. These phytoplasmas have recently been studied as a possible natural source of phytoplasmas that affect vineyards in France, Italy and Germany (Arnaud et al., 2007). The finding of AldY phytoplasmas infecting alders in Serbia could be of importance in revealing an epidemiological cycle of FD outbreaks in this area.