Forest Pathology

Abstract‘Candidatus Phytoplasma ulmi’, associated with elm yellows, shoot proliferation and dieback of elm (Ulmus) species trees was reported in United States of America and in many European countries. Until now its presence in elm trees in Poland has not been detected. In 2017–2018, during visual inspection of elm trees grown in four areas of southern Silesia Province leaf yellowing, shoot proliferation, phloem necrosis and dieback of branches were observed on European field elm trees grown in nature reserve close to the border with the Czech Republic. Phloem tissue from shoots collected from six symptomatic and twenty asymptomatic trees was used for extraction nucleic acids. Nested PCR with primer pairs amplifying 16Sr RNA sequences of phytoplasmas resulted in specific products for samples from six symptomatic trees however the restriction fragment length polymorphism (RFLP) and phylogenetic analyses of the sequenced products did not allow to clearly classify newly detected isolates within the elm yellows group (16SrV). The isolates found in Poland clustered on the boundary of the 16SrV‐A and 16SrV‐C ribosomal subgroups. Sequence analyses of less conservative genes rpl22‐ rps3 and secY confirmed the affiliation of the phytoplasma isolates found in Poland to ‘Candidatus Phytoplasma ulmi’; however, the significant nucleotide changes in signature sequences for all three genes were shown compared with EY1T reference strain. Surprisingly, the newly detected isolates shared a common origin and were phylogenetically closer to EY1‐SRB and EY10‐SRB strains from Serbia as well as NK16 strain from Croatia strains than to the EYCZ1 strain from the Czech Republic. This is the first report on detection and molecular characterization of ‘Candidatus Phytoplasma ulmi’ in Poland based on sequence analysis of three genetic locus.

AbstractIn order to devise a method for rapid detection of ‘Candidatus (Ca.) Phytoplasma pini’ and for distinguishing it rapidly from other phytoplasmas, we carried out preliminary sequencing of Lithuanian ‘Ca. Phytoplasma pini’ strain PineBL2 using Illumina (NGS) technology and targeted sequencing employing universal phytoplasma primers. We focused on two resulting chromosomal segments that contained a 16S rRNA gene and a translation elongation factor EF‐TU gene (tuf), respectively. Based on alignments of the ‘Ca. Phytoplasma pini’ gene sequences with the corresponding sequences of other phytoplasmas, we designed new primer pairs for PCR‐based detection of ‘Ca. Phytoplasma pini’. Because ‘Ca. Phytoplasma pini’ strains are expected to reside in the pine phloem in a very low titre, one might expect that they could be detected only by nested PCR. By contrast, the primers and PCR protocols designed in the current work enabled rapid direct PCR detection and identification of ‘Ca. Phytoplasma pini’ by amplifying a 484 bp 16S rDNA segment and a 513 bp tuf gene fragment that contain regions unique to this phytoplasma.

SummaryDuring summer of 2015, Eucalyptus camaldulensis plants showing witches’ broom, little leaf and general yellowing of the foliage were observed in west of Fars and Khozestan province of Iran. DNA from samples of 22 symptomatic and two asymptomatic trees was extracted and subjected to molecular analyses. Nested‐PCR test using R16F2n/R16R2 primers confirmed phytoplasma presence in 63% of symptomatic Eucalyptus plants. Sequence analysis along with virtual RFLP of the 16S ribosomal DNA allowed to classify three Eucalyptus witches’ broom strains into the “stolbur” (“Candidatus phytoplasma solani”) 16SrXII‐A subgroup. Comparison of the secA and secY gene sequences with sequences deposited in GenBank confirmed the phytoplasma identity. Real and virtual RFLPs of the amplified secY gene using HaeIII, MseI and RsaI restriction enzymes showed profiles indistinguishable from each other. This is the first study reporting E. camaldulensis as a new host species for “Ca. P. solani.”