engleski

Flower necrosis of Calendula officinalis L. caused by Alternaria alternata

Pot marigold or English marigold, Calendula officinalis L. (Asteraceae), is an ornamental species, grown in gardens or as potted plants all over Europe. After the discovery of its seed-oil content of around 20%, calendula has been cultivated not only as an attractive garden plant, but also for its flowers rich in essential oils and pigments and as an industrial crop. Potted calendula plants produced in a greenhouse in Krtinjska in Serbia exhibited flower necrosis and decay with incidence estimated at 80%. From diseased plants, as well as from ten samples of commercial calendula seed, a total of 20 monosporial isolates of Alternaria sp. were selected and identified based on morphological features. Their pathogenicity was tested by spore suspension injection of healthy calendula seedlings and by inoculation on nonwounded detached leaves. Intensive necrosis developed after 3-5 days on inoculated test plants and leaves. Further molecular detection and identification of Alternaria isolates was performed using polymerase chain reaction (PCR). Total DNA was extracted directly from fungal mycelium with a DNeasy Plant Mini Kit (Qiagen, Hilden, Germany) following the manufacturer's instructions. Molecular detection was conducted with a specific primer pair AAF2/AAR3 for the detection of A. alternata and they amplified a 340 bp fragment of all isolates. Two representative isolates, 2-10-1 and 58-10, originating from calendula seed and symptomatic calendula plants, were amplified and sequenced with primers ITS1F/ITS4 (HQ625053 and HQ625054, respectively). This isolates exhibited 100% nucleotide identity and were 99.8-100% identical to A. alternata isolates (EU781951, GU566303, GU797144, GU797138, FJ904919) in NCBI GenBank database. So far, Alternaria sp. was reported as a pathogen of C. officinalis in Bulgaria, Moldavia and North America, and this investigation revealed that A. alternata represents a treat to calendula production in Serbia as well.

Alternaria alternata; Calendula officinalis; flower necrosis

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