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First Report of White Mold Caused by Sclerotinia sclerotiorum on Borago officinalis in Italy

Borago officinalis L. (common borage) is a flowering plant belonging to the Boraginaceae with several culinary and medicinal uses and grown in soil or as potted plants in Liguria (northern Italy). At the end of winter in 2008, extensive chlorosis was observed on potted plants of B. officinalis grown in containers on a farm near Albenga (northern Italy). Initial symptoms included stem necrosis at the soil level and darkening of leaves. Disease was characterized by the presence of soft, watery tissues, particularly on affected leaves. As stem and foliar necrosis progressed, infected plants wilted and died. Wilt occurred within a few days on young plants. Symptomatic plants were found on 10 farms: average disease incidence in some nurseries reached 20%. Necrotic tissues became covered with a whitish mycelium that produced dark sclerotia. The diseased stem tissue was surface disinfected for 1 min in 1% NaOCl and plated on potato dextrose agar (PDA) amended with 100 ppm of streptomycin sulfate. Sclerotinia sclerotiorum (Lib.) de Bary (2) was consistently recovered from infected stem pieces. Sclerotia observed on infected plants at the soil level measured 2 to 9 × 1.5 to 7 (average 6 × 3) mm. Sclerotia produced on PDA measured 3 to 7 × 2 to 4 (average 4.4 × 3.1) mm. The internal transcribed spacer (ITS) region of rDNA was amplified using primers ITS4/ITS6 (3) and then sequenced. BLAST analysis of the 521-bp segment showed a 100% homology with the sequence of S. sclerotiorum. The nucleotide sequence has been assigned GenBank Accession No. EU627005. Pathogenicity of four isolates obtained from infected plants and used in mixture was confirmed by inoculating 10 30-day-old plants grown in 14-cm-diameter pots that were maintained in the greenhouse. Inoculum, consisting of 1-cm² mycelial plugs excised from a 10-day-old PDA culture of each isolate, was placed on the soil surface around the base of each plant. Ten noninoculated plants served as a control. Plants were covered with a plastic bag for 4 days after inoculation. The inoculation trial was repeated once. All plants were kept at an average temperature of 20°C and watered as needed. All inoculated plants developed symptoms of leaf yellowing within 4 days, followed by the appearance of white mycelium and sclerotia and eventual wilt. Control plants remained symptomless. S. sclerotiorum was reisolated from the stems of inoculated plants. To our knowledge, this is the first report of white mold on B. officinalis in Italy as well as in Europe. The disease was recently reported in North Dakota (1). The economic importance of this disease is currently low; however, the request of borage for culinary uses is increasing.

References: (1) C. A. Bradley et al. Plant Dis. 89:208, 2005. (2) N. F. Buchwald. Den. Kgl. Veterin.er-og Landbohojskoles Aarsskrift 5:1949. (3) D. E. I. Cooke and J. M. Duncan. Mycol. Res. 101:667, 1997.