Occurrence of powdery mildew on Lactuca viminea subsp. chondrilliflora in south France

Abstract

During the summer 1999 an expedition was conducted in seven European countries to collect wild Lactuca spp. germplasm and to study its geographic distribution and ecology. Natural infections by powdery mildew were recorded to. L. saligna and L. virosa plants found in south France (Provence) were free of powdery mildew infections. However, powdery mildew on L. viminea subsp. chondrilliflora was found. Based on the observations of the morphology of its anamorph stage and comparison with the species described on Lactuca spp. till now, the identity of this powdery mildew species is discussed. The comparison of powdery mildew collected on L. viminea subsp. chondrilliflora with Golovinomyces cichoracearum (≡ Erysiphe cichoracearum), the only species hitherto described on Lactuca spp., showed substantial differences in length of conidia and their shape index, conidiogenesis and number of distal conidial cells (Pseudoidium type). The occurrence of cleistothecia was not recorded. The fungus may be assigned to Erysiphe emend., and is probably a new species.