Raffaelea quercina sp. nov. Associated with Cork Oak (Quercus suber L.) Decline in Portugal

Filomena Nóbrega,Maria L Inácio,Edmundo Sousa,José Marcelino,Arlindo Lima

doi:10.3390/f12040513

Filomena Nóbrega, Maria L Inácio + Show 3 more

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https://doi.org/10.3390/f12040513

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Abstract

Research Highlights: Raffaelea quercina sp. nov. is an ophiostomatoid fungus isolated from the ambrosia beetle Platypus cylindrus. The species occurs in symptomatic Portuguese cork oak trees, (Quercus suber L.), exhibiting vegetative decline. Background and Objectives: Quercus suber L. is a species restricted to the Mediterranean basin, of special economic importance as it constitutes the crucial raw material for the cork production industry, in particular for Portugal, the world’s leading producer. Over the last three decades a progressive and alarming decline of cork oak trees has been observed across its distribution area, including Portugal. The ambrosia beetle Platypus cylindrus, commonly known as the oak pinhole borer, establishes symbiotic relationships with fungi from which it depends for survival and for oak colonization. Some of these fungi are ophiostomatoid species of the Raffaelea genus, known as ambrosia fungi associated with ambrosia beetles. Some Raffaelea species exhibit phytopathogenic activity causing wilting and/or death of trees. The objective of the present study is to identify the association between P. cylindrus and Raffaelea species in Portuguese cork oak stands showing symptoms of disease and decline. Materials and Methods: A total of 300 adult insects were collected as they emerged from cork oak logs, sampled from symptomatic trees. Axenic isolates of Raffaelea species were obtained from the beetles and their galleries in the trunks and identified based on morphological features and molecular analysis of the SSU and LSU rDNA regions. Results: Two Raffaelea species were identified, i.e., R. montetyi and a novel Raffaelea species closely related to R. canadensis. The novel species is morphologically and genetically characterized in this study, and erected as Raffaelea quercina M.L. Inácio, E. Sousa & F. Nóbrega, sp. nov. Raffaelea quercina constitutes a new phytopathogenic fungal species associated with P. cylindrus and cork oak trees exhibiting symptoms of vegetative decline. Conclusions: Raffaelea species appear to have a significant role in cork oak decline. Future research on the association between P. cylindrus and Raffaelea species, encompassing the trans-European and North African wide-range of cork oak stands, would further clarify the relationships between ambrosia beetles, associated fungi and cork oak decline, contributing to a better understanding of the phenomena and for strategies aiming to halt the continuous decline of the unique cork oak stands enclosed in the Mediterranean basin.

Highlights

The cork oak (Quercus suber L.) is an oak species native to the Mediterranean zones of southwest Europe and northwest Africa
Fungal isolations were performed directly from adult P. cylindrus emerged from symptomatic cork oaks, and from pieces of their galleries
Our previous works demonstrated that R. quercina is a pathogenic fungus towards Q. suber seedlings as R. montetyi, probably contributing to cork oak decline and to the establishment of its associated ambrosia insect, Platypus cylindrus

Summary

Introduction

The cork oak (Quercus suber L.) is an oak species native to the Mediterranean zones of southwest Europe and northwest Africa. In Portugal, cork oak landscapes (montados) cover approximately 720 thousand ha [1], providing a vital source of income, especially due to the ability to produce cork, a raw material widely used for wine bottle stoppers. Forests 2021, 12, 513 cover approximately 720 thousand ha [1], providing a vital source of income, especially due to the ability to produce cork, a raw material widely used for wine bottle stoppers. SSiinnccee tthhee 11889900ss,, aa ccoorrkk ooaakk ddeecclliinnee hhaass bbeeeenn rreeppoorrtteedd iinn ssoouutthhwweesstteerrnn PPoorrttuuggaall [[22]]. TThhee ooccccuurrrreennccee ooff tthhee ddeecclliinneewwaassaassssuummeeddaassaacocmomplpelxexphpehneonmomeneonnoncacuasuedsebdybtyhethineitnetrearcatcitoinonoof fmmuultlitpiplelebbioiotitcicaannddaabbiioottiiccffaaccttoorrss[[33]],, ssuucchh aass cclliimmaattiicc vvaarriiaattiioonnss((ddrroouugghhttaanndd ffrroosstt)),,eexxcceessssiivveehhaarrvveessttiinnggaannddpprruunniinngg,, aanndd aattttaacckkss ooff iinnsseecctt ppeessttss aanndd ppaatthhooggeennss [[44––77]].

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