A taxonomic re‐evaluation reveals that <i><scp>P</scp>hytophthora cinnamomi</i> and <i><scp>P</scp>. cinnamomi</i> var. <i>parvispora</i> are separate species

Abstract

Summary Between 2008 and 2011, severe dieback associated with root and collar rot was reported on A rbutus unedo in several sites in S ardinia, I taly. Isolations from infected tissues and rhizosphere soil samples consistently yielded a P hytophthora species. It was initially identified as P hytophthora cinnamomi var. parvispora K röber and Marwitz by comparing morphological features with the original description and the internal transcribed spacer ( ITS ) sequences with those present in G en B ank. A multigene phylogeny based on DNA sequence data from two nuclear ( ITS and β‐tubulin) and two mitochondrial ( cox 1 and cox 2) gene regions combined with extensive morphological and physiological properties of these isolates, including the ex‐type culture of P . cinnamomi var. parvispora , demonstrates that this taxon is unique and it is redesignated here as P hytophthora parvispora sp. nov. Although morphologically similar to P . cinnamomi , P . parvispora differs by its smaller‐sized sporangia, chlamydospores, oogonia and oospores, higher oospore wall index, single‐celled antheridia, higher minimum and maximum temperatures for growth and faster growth at optimum temperature. In the phylogeny, P . parvispora falls within P hytophthora ITS clade 7a, grouped in a well‐supported clade sister to P . cinnamomi . In pathogenicity tests, P . parvispora and P . cinnamomi were equally aggressive towards A . unedo seedlings. The possible geographic origin of P . parvispora is also discussed.