A Contribution to the Identity of Rhododendron Powdery Mildew in Europe

Rhododendron powde ry mi ldew has caused seriOlls di sease on o utdoor Rhododendron in Euro pe since 1981 yet its ide ntity i:\nd ori gins are still uncertain. Light and scanning electron microscope studies co nfirmed previo lls evidence thal conidial specimens all olltd oor Rhododendron in Euro pe a re mo rpho logica ll y simi la r. They co uld all be placed into the newly erected anamorph taxo n. OidiulII subgenus Pseudoidium . C leis to thecia of Allicrusphaero (coleoe o n decidu o us azalea (Rhodvdelldron/l.lleulI/) and evergreen rh ododendron ( Rhododelldroll hybrid and Rhodo( I£)l1drol1 /orltmei) arc described in dewil lo r the first lime in Europe from Bonn, Germany, together wilh the previo usly undescribed anamorph . An earlier record of ·M. ccaleaeʹ from Be lgium was shown to be a Ilew species, here described as M icrosphaera digiflU{f sp . nov. The pscucioiciiulll all Cl lll o rphs a ssociated with bo th M. a::a/elle and !vI. digitata were sim ilar to th ose examined on o utdoor Rhododendron in Europe. They a ll confo rmed to the d escription of Oidium eriCʹillulI1 from Rhododendroll and o ther Ericaceac. These two Microsphacra species are the first rhododendro n powdery mildews in Europe fo r which the teleomorph a namorph connecli o ns ha ve been described . The possible identities of rhododendron powdery mildews in Europe are discussed .