Variability in morphology of Microsphaera alphitoides Griffon et Maubl. in Poland

Abstract

The aim of this study was to verify descriptions of the morphology of the fungus responsible for powdery mildew on oak leaves of nursery seedlings and of young trees in forest stands. Infected, fully developed leaves from apical parts of stems of Quercus robur or Q. petraea were collected in two national parks and in six forest districts in Poland. The taxonomic characteres of all specimens were generally consistent with those given in keys for Microsphaera alphitoides. However, the limoniform shape of conidia, characteristic of two sites (nurseries), has not been found in available synopses. Limoniform conidia were significantly longer and wider than others. Agreat variety of forms of mycelium on leaves were observed. The mycelium appeared in three forms: (1) floccose or felted oval patches (always with yellow or brown discoloration), (2) faveolate oval patches (often with yellow or brown discoloration), and (3) felted or mealy mycelium along veins (rarely with discoloration). Mycelium without limoniform conidia appeared in all forms, while mycelium with limoniform conidia appeared only in the form of patches, always causing leaf discoloration.