Molecular Identification of Phytoplasmas Infecting Diseased Pine Trees in the UNESCO-Protected Curonian Spit of Lithuania

Deividas Valiunas,Rasa Jomantiene,Robert Davis,Algirdas Ivanauskas,Donatas Sneideris,Indre Urbonaite

doi:10.3390/f6072469

Deividas Valiunas, Rasa Jomantiene + Show 4 more

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https://doi.org/10.3390/f6072469

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Abstract

Although mainly known as pathogens that affect angiosperms, phytoplasmas have recently been detected in diseased coniferous plants. In 2008–2014, we observed, in the Curonian Spit of Western Lithuania and in forests of Southern Lithuania (Varena district), diseased trees of Scots pine (Pinus sylvestris) and mountain pine (Pinus mugo) with unusual symptoms similar to those caused by phytoplasmas. Diseased trees exhibited excessive branching, dwarfed reddish or yellow needles, dried shoots and ball-like structures. restriction fragment length polymorphism (RFLP) and nucleotide sequence analysis of 16S rRNA gene fragments revealed that individual trees were infected by Candidatus (Ca.) Phytoplasma pini-related strains (members of phytoplasma subgroup 16SrXXI-A) or by Ca. Phytoplasma asteris-related strains (subgroup 16SrI-A). Of the nearly 300 trees that were sampled, 80% were infected by phytoplasma. Ninety-eight percent of the positive samples were identified as Ca. Phytoplasma pini-related strains. Strains belonging to subgroup 16SrI-A were identified from only few trees. Use of an additional molecular marker, secA, supported the findings. This study provides evidence of large-scale infection of Pinus by Ca. Phytoplasma pini in Lithuania, and it reveals that this phytoplasma is more widespread geographically than previously appreciated. This is also the first report of phytoplasma subgroup 16SrI-A in pine trees.

Highlights

In Lithuania, the timber industry generates about 2% of industrial production and engages 13% of the nation’s workforce
Our recent experimental results have revealed that the timber industry in Lithuania may be threatened by yet another disease caused by a phytoplasma; in this case, the disease is affecting gymnosperms, Scots (Pinus sylvestris L.) and mountain (Pinus mugo Turra) pines
All seven naturally infected Scots pines in the Varena district in southern Lithuania exhibited the same symptoms of excessive branching, dwarfed needles and dried shoots (Figure 1a)

Summary

Introduction

In Lithuania, the timber industry generates about 2% of industrial production and engages 13% of the nation’s workforce. Timber, including wood from pine trees, is an economically important Lithuanian export commodity, and Scots pine (Pinus sylvestris L.) is highly valued in the wood industry for supplying raw materials for products including furniture, paper, firewood, cork, and wood-pulp [1]. Diseases caused by phytoplasmas in forest trees, including alder, willow, and oak, have already been reported in Lithuania [2,3,4]. Our recent experimental results have revealed that the timber industry in Lithuania may be threatened by yet another disease caused by a phytoplasma; in this case, the disease is affecting gymnosperms, Scots (Pinus sylvestris L.) and mountain (Pinus mugo Turra) pines. Mountain pines were introduced since the mid-1800s for dune protection from deflation [5]

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