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Phytophthora cryptoea on Common Sage (Salvia officinalis L.) in Italy

During the spring of 2013, many plants of common sage (Salvia officinalis L.), grown as potted plants in a commercial farm at Albenga (northern Italy) showed extensive symptoms of foliar wilt and root rot. The first symptoms developed with temperatures ranging between 8 and 26.5°C, average 17°C, and consisted of leaf chlorosis, wilting, and collapse. Severe root and crown rot were also observed, leading to sudden collapse of approximately 60% of the 6,000 plants within 60 days from transplant. Symptomatic tissues from the root and collar of infected plants were surface disinfested for 1 min in a 1% NaOCl solution, rinsed for 5 min in water, and placed on a selective medium for oomycetes (3). A Phytophthora-like organism (1) was consistently isolated and was transferred to carrot agar. Mycelial disks of the isolate DB13GIU02 were floated in petri plates containing soil extract (1), under continuous fluorescent light at room temperature. Hyphal swelling was abundant in such aqueous medium, measuring 6.4 to 20.1 (13.1 average) μm. Sporangia were obpyriform, persistent, and nonpapillate, measuring 25.3 to 55.1 × 17.9 to 37.1 (average 42.8 to 27.9) μm. Oospores and chlamydospores were absent. The same isolate was tested with two isolates of P. cryptogea from Quercus ilex (PH050, mating type A1) and from Pistacia lentiscus (PH017, mating type A2) on carrot agar, at 23 ± 1°C in the dark. Only the paring of DB13GIU02 with PH017 was successful and produced oogonia with diameter of 28.3 to 34.6 (average 31.7) μm, oospores with diameter of 28.0 to 32.2 (average 29.2) μm, and anphigynous antheridia of 10.5 to 15.1 × 11.6 to 15.1 (average 13.5 × 13.3) μm. DNA of the three isolates was extracted by using the Nucleospin Plant kit (Macherey Nagel). PCR of DNA amplified with primers Cryp 1 and Cryp 2 (4) from all P. cryptogea isolates produced a specific amplicon. The internal transcribed spacer (ITS) region of rDNA of the isolate DB13GIU02 was amplified using the primers ITS1/ITS4 and sequenced. BLAST analysis of the 845-bp segment (GenBank Accession No. KM458193) showed a 99% homology with the sequence of P. cryptogea GU111631. Pathogenicity tests were performed on healthy common sage 60-day-old plants by using one strain of P. cryptogea grown on a mixture of 2:1 wheat/hemp kernels. Infested kernels (10 g/liter of substrate) were mixed into a steam-disinfested substrate based on sphagnum peat/pomix/pine bark/clay (50:20:20:10 v/v). Control plants were treated with uninoculated wheat/hemp kernels mixed into the steam-disinfested soil. The trial was repeated once. Fifteen plants per treatment were used. All plants were kept in a growth chamber at 20 ± 1°C. Inoculated plants became chlorotic 7 days after inoculation, and root and crown rot developed 15 days after inoculation. P. cryptogea was consistently reisolated from inoculated plants. No colonies were isolated on the selective medium from control plants that remained symptomless. P. cryptogea has been reported on S. officinalis in the United States (2), while in Italy the same pathogen has been observed on S. leucantha. This is the first report of P. cryptogea on S. officinalis in Italy. The economic importance of the disease can increase due to the expanding use of this plant both as an aromatic for culinary purposes and for landscaping.

References: (1) D. C. Erwin and O. K. Ribeiro. Phytophthora Diseases Worldwide. APS Press, St. Paul, MN, 1996. (2) S. T. Koike et al. Plant Dis. 81:959, 1997. (3) H. Masago et al. Phytopathology 67:25, 1977. (4) D. Minerdi et al. Eur. J. Plant Pathol. 122:227, 2008.