Archivio Journal of Plant Pathology

Abstract:

Oenothera biennis, family Onagraceae, is a biennial species used as border and potted plant. In summer 2011, severe out- breaks of a powdery mildew were observed in a private garden near Biella (northern Italy). Leaves were covered with a dense white mycelium, especially on the adaxial surface, which was also present on stems, pedicels of flowers and bracts. Conidia were hyaline, ellyptical, borne singly, and measured 25.0-38.4×17.8- 25.4 (average: 31.5×21.0) μm. Germ tubes were produced termi- nally. Fibrosin bodies were absent. Conidiophores were erect, with a cylindrical foot cell measuring 18.0-49.4×7.5-9.6 (average: 30.9×8.4) μm, followed by 1-2 shorter cells, measuring 15.5- 35.0×8.8-12.8 (average: 22.5×10.5) μm. Chasmothecia were not observed. The ITS region of rDNA was amplified using primers ITS1/ITS4 and sequenced (Altschul et al., 1997) (GenBank ac- cession No. JQ288740). The amplified 603 bp product showed 98% similarity with a comparable sequence of Erysiphe pisi. To determine pathogenicity, diseased leaves of O. biennis were pressed against leaves of four healthy plants of the same host. Four plants of Pisum sativum were also inoculated. Controls con- sisted of four non-inoculated plants for each tested species. Plants were maintained at temperatures from 23 to 33°C. Symp- toms were reproduced only on inoculated plants of O. biennis. The pathogen was retained as Erysiphe sp. since P. sativum re- mained healthy. E. howeana was reported on O. biennis in several European countries (Braun, 1995) as well as in New Zealand, while E. polygoni was reported in the USA (Farr et al., 1989).