Identification of an Emaravirus in a Common Oak (Quercus robur L.) Conservation Seed Orchard in Germany: Implications for Oak Health

Martina Bandte,Carmen Büttner,Marius Rehanek,Bertram Leder,Susanne Von Bargen

doi:10.3390/f11111174

Abstract

We observed the health status of oak trees in a conservation seed orchard for over twenty years, focusing on characteristic virus-suspected symptoms. The orchard was established in 1992 in Kreuztal, North Rhine-Westphalia (Germany) with 1302 seedlings in 186 clusters. The number of seedlings showing chlorotic ringspots and mottle on leaves has fluctuated annually, but has increased from 3.3% to 12.1% in the last 20 years; the number of affected clusters has risen from 8% to 25.9%. A scientific breakthrough was the identification of a novel virus related to members of the genus Emaravirus in diseased oak by high-throughput sequencing (HTS). Screening of the oak seedlings in three consecutive years, using a newly established virus-specific diagnostic reverse transcription polymerase chain reaction (RT-PCR), confirmed the virus infection and revealed a close to 100% association between the observed leaf symptoms and the novel virus. As no other plant virus could be identified in the HTS-datasets, we assume the novel virus is primarily causing the symptoms. To reliably detect the novel virus in oaks, RT-PCR targeting the viral RNA3 or RNA4 should be applied in routine testing of symptomatic leaf tissue. It was obvious that most groups with virus-infected plants cluster, with only five out of the 42 affected groups being offside, not bordering on other affected groups of plants. There was no clear correlation between the detection of the virus and the overall vitality of the seedlings. There was no relation between seedling performance and presence or absence of viral infection. Forecasts on the future growth behavior of these virus-infected oak trees are therefore not possible.

Highlights

Quercus robur (L.), commonly known as common oak, pedunculate oak, or European oak, is a very widespread species which is native to most of Europe and described as a vigorous tree with a large ecological amplitude [1]
BLASTX search of contigs performed in the NCBI database identified six contigs relating to RNA1 to RNA4 encoded by different emaraviruses (Table 1)
Nearly 50% of oak forests are established by planting due to the difficulties in regenerating oaks naturally [21]. This is the case where competition from herbaceous and woody vegetation hinders the natural regeneration of oak or when coniferous stands are to be converted to oak forests and acorn sources are lacking

Summary

Introduction

Quercus robur (L.), commonly known as common oak, pedunculate oak, or European oak, is a very widespread species which is native to most of Europe and described as a vigorous tree with a large ecological amplitude [1]. Oaks are amongst the most economically and ecologically important deciduous trees in Europe providing wood for fuel, bark for tanning, timber for construction, and acorns for livestock. Across 34 European countries, pedunculate oak covers approximately 49,000 km2 [2]. In Germany, oak species can be found on around 10% of forested land, making oaks the second most important deciduous tree species after European beech (Fagus sylvatica L.) [3]. The production of high-quality wood is associated with long rotations and high labor costs.

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