Peronospora agrestis Gaum.
Year: 2026
Type: article
Abstract: Peronospora agrestis Gäum., Annales Mycologici 16 (1–2): 198. 1918. Fig. 2 Description. Lesions on leaves at first yellowish, later dark yellow to brown, diffuse to vein-delimited. Down present on the lower leaf surface, consisting of scattered to dense felt-like conidiophore outgrowth. Conidiophores hyaline, straight to curved, thin-walled, 271–396 µm long, av. 334 µm; trunk 156–243 µm long, av. 200 µm, 6.5–9 µm broad, sometimes slightly swollen to up to 13 µm at the base, ratio of the total length to trunk length 1.5–2, callose plugs absent. Branching subdichotomous in 4–6 orders, with sub-straight to curved branches, gradually attenuate, often at right angles. Ultimate branchlets sub-straight to curved, paired branchlets differing in length, with the longer ones 9.5–15.5 µm long, the shorter ones 6.5–11 µm long, with a ratio of the longer to the shorter ultimate branchlet of 1.2–1.65, base 2–2.5 µm broad, apex slightly sharp. Conidia ellipsoid to ovoid with a dark brown colour, 20–22.5 µm long, 15–17 µm broad, length-to-breadth ratio 1.25–1.4, basal part of the conidia mostly protruding. Oospores not observed. Type host. Veronica polita (Gäumann 1918; Stevenson 1926). Reported hosts. Veronica agrestis (Gäumann 1918; Stevenson 1926; Dennis 1986), V. arvensis (Dennis 1986), V. polita (Gäumann 1918; Stevenson 1926), V. opaca (Notizen 1934), Veronica chamaedrys (Voglmayr 2003). Reported distribution. Austria, Russia, Spain, Switzerland (Gäumann 1923; Stevenson 1926; Voglmayr 2003). Specimens examined. AUSTRIA. Lower Austria: Mödling, Guntramsdorf, gappy embankment at Weingarten, on living leaves of Veronica polita, 4 Apr 2004, H. Voglmayr (WU-MYC 0032792). GERMANY. Baden-Württemberg: Tübingen, on living leaves of Veronica filiformis, 28 Apr 2001, H. Voglmayr (WU-MYC 0032787); Bayern: unknown, on living leaves of Veronica filiformis, 10 May 2013, J. Kruse (J. K. 0460); Saxony: Dresden, on living leaves of Veronica filiformis, 11 July 1988, H. Jage (GLM-F 068565); Hermsdorf, on living leaves of Veronica persica, 28 Jun 1998, H. Jage (GLM-F 074038); Saxony-Anhalt: Lammsdorf, on living leaves of Veronica persica, 25 May 2002, H. Jage (GLM-F 078101); Kemberg, on living leaves of Veronica polita, 29 Sep 1984, H. Jage (GLM-F 068541); Saaleck, on living leaves of Veronica persica, 19 Jun 2003, H. Jage (GLM-F 073381). Unknown, on living leaves of Veronica persica, unknown, M. Thines (M. 600). Notes. Peronospora agrestis has been reported in Europe infecting various hosts, including Veronica agrestis, V. arvensis, V. chamaedrys, V. opaca, and V. polita (Gäumann 1918, 1923; Stevenson 1926; Notizen 1934; Dennis 1986; Voglmayr 2003), with V. polita being the type host of P. agrestis. However, our phylogenetic analysis reveals that P. agrestis is restricted to its type host, V. polita, and closely related hosts V. filiformis and V. persica. The Peronospora species found on V. arvensis represents a distinct, previously undescribed taxon, which is phylogenetically distinct from P. agrestis infecting V. polita, V. filiformis, and V. persica across all phylogenetic trees. Furthermore, an ITS sequence, AY 198243, from specimen WU-MYC 0022873 collected in Austria on Veronica chamaedrys was previously identified as P. agrestis (Voglmayr 2003). However, our ITS phylogenetic tree shows that this sequence does not form a clade with P. agrestis, but rather with two other specimens from Germany, also parasitic on V. chamaedrys, suggesting that V. chamaedrys is not a host of P. agrestis, but a previously undescribed species. Phylogenetic analyses indicate that P. agrestis has two closely related sister species, P. fidelia and P. gracilis, which were previously undescribed. However, P. fidelia and P. gracilis are characterised by shorter conidiophores and trunks, with lengths shorter than 300 µm and 200 µm on average, respectively.
Language: English
Subfield: Plant Science
Domain: Life Sciences
SDG: Zero hunger
Open Access status: green
OpenAlex ID: W7140188941