Powdery mildew (Erysiphe cruciferarum) infection on camelina (Camelina sativa) under Mediterranean conditions and the role of wild mustard (Sinapis arvensis) as alternative host of this pathogen

Abstract

During the growing season 2014-2015, camelina (Camelina sativa (L.) Crantz) plants were naturally infected by powdery mildew at the province of Domokos in Central Greece. Moreover, wild mustard (Sinapis arvensis L.) plants, naturally occurring in camelina field, were infected by the disease. The environmental conditions that influence infection of camelina by powdery mildew were recorded. The anamorph as well as the teleomorph of the fungus pathogen were observed on symptomatic leaves, stems and fruits of camelina and wild mustard plants. Fungal specimens were examined. Conidiophores were cylindrical and comprised 3 cells, while conidia were produced singly; they were oblong to cylindrical and measured 21.8 to 40.5 × 9.4 to 18.4 μm (average 32.1 × 13.9 μm). Chasmothecia were also observed on the upper surface of camelina or wild mustard leaves and on wild mustard siliques. Immature chasmothecia were globose, yellow and turned dark brown as reached maturity. Each chasmothecium contained six asci that measured 47.6 to 74.5 × 29.8 to 44.7 μm. Based on these characteristics the pathogen was identified as Erysiphe cruciferarum Opiz ex L. Junell, being probably the first report of E. cruciferarum on camelina in Greece.