Downy mildew outbreak on parsley caused by Plasmopara petroselini in Turkey

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 .