FIRST REPORT OF WHITE MOULD CAUSED BY SCLEROTINIA SCLEROTIORUM ON ROSEMARY IN ITALY

Abstract

In the winter of 2017, in a commercial farm located in Albenga (northern Italy), about 300 6-month-old potted plants of Rosmarinus officinalis growing in a potting mix made up of peat and fertilizer (ca. pH 6 and E.C. 600 µS) showed symptoms of white mould. Affected leaves and stems became pale brown, withered and were covered by a whitish mycelium that produced dark sclerotia. Finally, affected plants rotted and died. Little pieces of mycelium were taken from affected tissues and white colonies developed on potato dextrose agar producing sclerotia similar to those previously observed. Symptoms and signs as well as morphological characteristics observed in vitro permitted to identify the causal agent of the disease as Sclerotinia sclerotiorum. The Internal Transcribed Spacer (ITS) region of rDNA belonging to the isolate DB17GEN01 was amplified using the primers ITS1/ITS4 and sequenced (GenBank Accession No. KY947523). BLAST analysis (Altschul et al., 1997) of the 518 bp amplified sequence showed 100% homology with the sequence of S. sclerotiorum KX184720. Five plants of R. officinalis were inoculated by placing at the collar wheat kernels (3 g/l) colonized by mycelium and sclerotia (Bohar and Kiss, 1999). Five control plants were treated with sterilised kernels without inoculum. All plants were maintained in a humid chamber (average temperature 22.2-23.0°C; RH 76.4- 89.5%). Four days post inoculation, browning appeared on leaves and stems of inoculated plants that were colonised by a whitish mycelium and withered. S. sclerotiorum was constantly reisolated from affected plants, whereas controls remained symptomless. S. sclerotiorum was reported on R. officinalis in India and in the United States (Putnam, 2004). To our knowledge, this is the first report of S. sclerotiorum on R. officinalis in Italy and in Europe. This disease could cause economic losses due to the widespread cultivation of rosemary in Italy.