New Disease Reports (2009) 20, 10.

Downy mildew outbreak on parsley caused by Plasmopara petroselini in Turkey

S. Soylu*, E.M. Soylu and Ş. Kurt

*soylu@mku.edu.tr

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Accepted: 06 Oct 2009

Flat-leafed parsley (Petroselinum crispum var. neapolitanum) is one of the most commercially important vegetable crops in the eastern Mediterranean region of Turkey . In February 2009, downy mildew symptoms were observed in several fields inspected in Hatay province. Incidence of downy mildew infection was 40-60 %, but in some locations it was as high as 95-100 %. Initial symptoms appeared as faint chlorotic spots on the upper surfaces of the leaves. On the corresponding lower surfaces, white to off- white mycelium and sporangiophores developed which eventually turned dark grey. The leaves and stalks became shriveled and necrotic, eventually dying (Fig.1). The tree-like sporangiophores (120-300 x 7.5-10.0 µm), which emerged in groups from the stomata (up to 10 in a fascicle), were hyaline, straight or slightly curved with a slightly swollen base, monopodially branched, each branch ending in two to five ultimate sterigmata tapered towards the tip. The sporangia were hyaline, broadly ellipsoidal to ellipsoidal, 22.5-30.0 x 12.5- 7.5 µm, with a length/width ratio = 1.28-1.55. A short conical pedicel (1.2 µm) was mostly present on mature sporangia which exhibited a dehiscence apparatus. Encysted zoospores were 5.0-7.5 µm in diameter (Figs.2 and 4). Oospores were not observed on the infected leaves. On the basis of symptoms and morphology of the organism, the pathogen was identified as Plasmopara petroselini (= P. umbelliferarum pro parte = P. nivea pro parte = P. crustosa) (Constantinescu et al., 2005).

Pathogenicity was confirmed by inoculating foliage of five-week-old parsley plants (cv. d’giant Italiana) with a suspension of sporangia (105 sporangia/ml). Inoculated plants were kept in a moist chamber (90 % RH) at 18° C for 48 h and then moved to a growth chamber at 20° C with a 16 h photoperiod. Symptoms and signs of downy mildew developed after 12 days only on inoculated plants, and the pathogen morphology matched Plasmopara petroselini. A voucher specimen was deposited at the MKU Herbarium and Culture Collection (MS-310904).

The disease has been previously reported to cause severe damage to parsley grown in European countries, e.g., Belgium, Sweden and Czech Republic (Crepel & Inghelbrecht, 2003; Amein et al., 2006; Muller & Kokes, 2008). To our knowledge, this is the first report of P. petroselini on parsley in Turkey .

Figure1+
Figure 1: Heavy sporulation on the lower surface of parsley leaves infected with Plasmopara petroselini
Figure 1: Heavy sporulation on the lower surface of parsley leaves infected with Plasmopara petroselini
Figure2+
Figure 2: Monopodially branched sporangiophores and sporangium (Sp) (Bar = 50 μm)
Figure 2: Monopodially branched sporangiophores and sporangium (Sp) (Bar = 50 μm)
Figure3+
Figure 3: Sporangia on sporangiophore (stained with trypan blue, Bar = 20 μm)
Figure 3: Sporangia on sporangiophore (stained with trypan blue, Bar = 20 μm)
Figure4+
Figure 4: Encysted zoospore (Zsp) with short germ-tube (Bar = 10 µm)
Figure 4: Encysted zoospore (Zsp) with short germ-tube (Bar = 10 µm)

References

  1. Amein T, Olsson CHB, Wikström M, Findus R, AB D, Wright SAI, 2006. First report in Sweden of downy mildew on parsley caused by Plasmopara petroselini. Plant Disease 90, 111.
  2. Constantinescu O, Voglmayr H, Fatehi J, Thines M, 2005. Plasmoverna gen. nov., and the taxonomy and nomenclature of Plasmopara (Chromista, Peronosporales). Taxon 54, 813-821.
  3. Crepel C, Inghelbrecht S, 2003. First report of Plasmopara petroselini on parsley in Belgium . Plant Disease 87, 1266.
  4. Muller J, Kokes P, 2008. Extended checklist of downy mildews of Moravia and Czech Silesia. Czech Mycology 60, 91-104.

This report was formally published in Plant Pathology

©2009 The Authors