Identification of<i>Armillaria</i>species on declined oak in Britain: implications for oak health

Abstract

The identity of 51 isolates of &lt;it&gt;Armillaria&lt;/it&gt; from 15 &lt;it&gt;Quercus robur&lt;/it&gt; trees in poor health, and a single healthy tree, at nine sites in England, was determined using multilocus sequence analysis (MLSA) of three gene regions. Sequences of the ITS-1, IGS-1 and EF-1α gene regions were obtained by polymerase chain reaction (PCR) amplification and sequencing, and phylogenetic trees were generated based on maximum likelihood and Bayesian inference of phylogenies. Four &lt;it&gt;Armillaria&lt;/it&gt; species were isolated: &lt;it&gt;Armillaria gallica&lt;/it&gt;, &lt;it&gt;A. mellea, A. ostoyae&lt;/it&gt; and &lt;it&gt;A. tabescens&lt;/it&gt;. &lt;it&gt;Armillaria gallica&lt;/it&gt; was most frequently isolated (40/51 isolates), but only from woodland trees. &lt;it&gt;Armillaria mellea&lt;/it&gt; was isolated infrequently (3/51), from garden trees; &lt;it&gt;A. tabescens&lt;/it&gt; was isolated infrequently (4/51), from trees either in a garden or a parkland location. &lt;it&gt;Armillaria ostoyae&lt;/it&gt; (4/51 isolates) was co-isolated with &lt;it&gt;A. gallica&lt;/it&gt;, raising interesting questions about the synecology of these species, suggesting that more thorough investigations are required to detect all species present on a single host. The distribution of these &lt;it&gt;Armillaria&lt;/it&gt; species in Britain and historical information about them on oak are described. It is concluded that further studies are necessary to determine the role of &lt;it&gt;Armillaria&lt;/it&gt; in oak declines; &lt;it&gt;A. gallica&lt;/it&gt; should be a key focus, but investigations should include polymicrobial interactions with other microorganisms, including other &lt;it&gt;Armillaria&lt;/it&gt; species.