engleski

Plasmopara obducens - a new pathogen on Impatiens walleriana in Serbia

Impatiens (Impatiens spp.) is very popular ornamental plant in Serbia. Because of its decorative properties, impatiens is frequently used in public parks and gardens, and that is the main reason for its growing rate of production in Serbia. Potted I. walleriana produced in a greenhouse in the locality of Mionica in Serbia were showing symptoms of stunting, with mild yellowing on the upper surface of the leaves. The lower surface of the affected leaves was covered with white fungal-like growth. Symptomatic leaves wilted and abscised from the stem, leaving plants with only a few of the youngest leaves and no or few flowers. Disease incidence was high, wilting and collapse of affected plants were very rapid, resulting in losses of more than 90%. Microscopic examinations revealed that white downy growth developing on leaf surfaces consist of hyaline sporangiophores with monopodial branching and numerous, ovoid and hyaline sporangia. Pathogenicity was tested by spraying with a sporangial suspension on young I. walleriana plants, and downy mildew symptoms were observed after 13-15 days. Molecular identification included total DNA extraction from plant tissue with a DNeasy Plant Mini Kit (Qiagen) and the amplifiication of the 5′-end of the nuclear DNA coding for the LSU rDNA by PCR using primers NL1/NL4. A representative isolate, 28-10, was sequenced in both directions (Accession No. HQ246451). A Neighbor-joining tree obtained on a 649-bp fragment of Plasmopara spp. isolates available in GenBank database revealed that Serbian isolate 28-10 was clustered with other P. obducens isolates. So far, the presence of P. obducens was recorded in Bulgaria, the Czech Republic, Denmark, Finland, Lithuania, Romania, Russia, the United Kingdom and recently in Norway. It is a serious threat to impatiens production in Serbia as well, especially regarding certain unclarified epidemiological aspects.

Impatiens walleriana; pathogen; Plasmopara obducens

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