Conidia of true Ampelomyces isolates are produced in pycnidia developed intracellularly in
the mycelia of powdery mildew fungi (Figures 1b and 2). Conidia are unicellular, hyaline,
mostly guttulate and are embedded in a mucilaginous matrix inside the pycnidia. In the
presence of water, these matrices swell and conidia are released from intracellular pycnidia as
a cirrhus by the rupture of the pycnidial wall. In ca. 10/20 h under conditions of high
humidity, conidia germinate and the hyphae of the mycoparasites can then penetrate the
hyphae of powdery mildews in their vicinity. The concentration of Ampelomyces conidia on
the leaves is also relevant as Gu and Ko (1997) showed that germination rapidly decreases
above a concentration of 106cfu ml1 due to the production of a self inhibitor. After
penetration, the hyphae of the mycoparasite continue their growth internally and produce
their intracellular pycnidia after 5/8 days in the mycelia of their host fungi (Figure 1b). A
high RH of the environment enhances the internal growth and sporulation of Ampelomyces
(Jarvis & Slingsby, 1977; Philipp & Cru¨ger, 1979).