Watercress is an aquatic dicotyledonous vegetable belonging to Brassicaceae (Aiton 1812). Watercress was grown in an aquaponic system on a fired clay ball medium at the Aquaponic Research Station of the University of Debrecen (Hungary). In January 2020, 3-month-old plants showed symptoms in aquaponic cultivation.
A visual survey showed 30% of plants with symptoms. Leaves and stems withered and showed white cotton-like mycelium. Mycelia from infected plants were placed on potato dextrose agar (PDA) and incubated at 25°C for seven days. Single hyphal tips were transferred to produce a pure culture. All ten fungal isolates showed similar morphological characteristics on PDA. Colonies consisted of white mycelia after three days and globoid to irregular and black 2.5 to 7 (average, 3) mm (n = 100 from ten plates) sclerotia formed ten days later, which are the typical morphological features of Sclerotinia sclerotiorum (Mordue et al. 1976).
Molecular identification was performed with one of the ten isolates (Scl_B). Mycelia were grown in 250 ml of potato dextrose broth in a rotary shaker at 175 rpm at 24°C for six days. DNA was extracted from mycelium using a Nucleospin plant II (Macherey-Nagel, Germany) according to the manufacturer's protocol. PCR amplification (Kim et al. 2014) was performed with primers ITS1/ITS4 for the internal transcribed spacer region (White et al. 1990) on a Primus 96 thermal cycler (MWG Biotech, Germany).
Similar results were detected in three repeated experiments with white mold fungus being reisolated from all 45 infected watercress plants. The 45 non-inoculated plants did not show any symptoms or diseases. This pathogen has already been reported on watercress in the field (Farr et al. 1989; Boland and Hall 1994; Garibaldi et al. 2019). This is the first reported case of white mold on watercress in aquaponic system in Hungary.
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Csüllög, Kitti & Tóth, Brigitta & Lelesz, Éva & Fehér, Milán & Virág, István & Kutasy, Erika & Jász, Brigitta & Tarcali, Gábor & Biró, Györgyi. (2022). First report of Sclerotinia sclerotiorum on watercress (Nasturtium officinale) in aquaponic system in Hungary. Plant Disease. 16. 767. 10.1094/PDIS-07-21-1472-PDN.