First Report of Collar and Root Rot Caused by Phytophthora tentaculata on Witloof Chicory (Cichorium intybus) in Italy

Abstract

Witloof chicory (Cichorium intybus L.) is an important crop in Italy where most of the crop is still produced in soil. In September 2009, chicory plants (cv. Pan di Zucchero) grown on a commercial farm in Tarquinia (central Italy) showed symptoms of a previously unknown disease. Symptoms, observed 20 days after transplanting, consisted of stunting, yellowing of leaves, and a crown and root rot. Affected plants turned brown, wilted, and eventually died. At the soil level, dark brown-to-black water-soaked lesions coalesced and often girdled the stem. All of the crown and root system was affected. At this location, the disease was severe and widespread, with 60% of observed plants being affected. A Phytophthora-like organism was consistently isolated on a medium selective for oomycetes (4) after disinfestation of lower stem and root pieces of C. intybus for 1 min in a solution containing 1% NaOCl. Tissue fragments of 1 mm2 were excised from the margins of the root and crown lesions. The pathogen genus was identified as Phytophthora based on morphological and physiological features. Sporangia were produced for identification by growing a pure culture for 15 days on modified V8 juice agar medium (Campbell V8 juice [200 ml], agar [15 g], CaCo3 [0.5 g], and sterile water [800 ml]) under alternating light and dark (12/12 h). Sporangia were pyriform to ovoid, papillate, and measured 33.3 to 59.2 × 18.9 to 30.2 μm (average 39.9 × 25.8 μm). Chlamydospores developed in 28-day-old cultures and measured 21.3 to 30.2 × 19.5 to 29.7 μm (average 24.4 × 23.6 μm). Oogonia were globose and measured 26 to 41 μm (average 32.5 μm). Eighty percent of antheridia were paragynous. Amphyginous antheridia (15 to 20%) were also observed. Oospores were scarcely produced and measured 24 to 32 μm in diameter. The internal transcribed spacer (ITS) region of rDNA of a single isolate was amplified using the primers ITS4/ITS6 and sequenced. BLAST analysis (1) of the 851-bp segment showed 100% homology with the sequence of Phytophthora tentaculata. The nucleotide sequence has been assigned GenBank Accession No. GU949536. Pathogenicity of this isolate was confirmed by inoculating C. intybus cv. Pan di Zucchero plants 20 days after transplant. The same isolate was grown for 15 days on a mixture of 70:30 wheat/hemp kernels and then 5 g/liter of the inoculum was mixed into a substrate containing a mixture of blond and black peat (15:85 vol/vol), pH 5.5. Five plants per 2-liter pot were transplanted and four replicates were carried out. Twenty noninoculated plants represented the control treatment. The trial was repeated. Plants were kept in two growth chambers at two temperatures (20 and 25°C). Symptoms similar to those observed in the field developed 7 days after inoculation. Twenty days later, 100 and 40% of the plants were dead at 25 and 20°C, respectively. Control plants remained symptomless. P. tentaculata was consistently reisolated from symptomatic plants. To our knowledge, this is the first report of P. tentaculata on C. intybus in the world ( http://nt.ars-grin.gov/fungaldatabases/index.cfm ). P. tentaculata was recently reported on lavender in Spain (2) and oregano in Italy (3). The economic importance of this disease is relatively low on most commercial farms. References: (1) S. F. Altschul et al. Nucleic Acids Res. 25:3389, 1997. (2) L. Alvarez et al. Plant Dis. 90:523, 2006. (3) P. Martini et al. Plant Dis. 93:843, 2009. (4) H. Masago et al. Phytopathology 67:425, 1977.