Peronospora fidelia M. Mu & Thines 2026, sp. nov.

Peronospora fidelia M. Mu & Thines sp. nov. Fig. 7 Etymology. Veronica symbolizes loyalty, the epithet is derived from Latin “ fides ” (loyal), which refers to the symbolism of flowers. Diagnosis. Differs from P. agrestis in having larger conidia, as well as shorter conidiophores and trunks. Differs from P. gracilis in having larger and more elongated conidia, as well as longer ultimate branchlets. Type. GERMANY. Saxony-Anhalt: Annaburg southwest, on living leaves of Veronica triphyllos, 1 May 2004, H. Jage (holotype GLM-F 063005). Description. Lesions on leaves at first pale green, later expanding to dark 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, 238–352 µm long, av. 295 µm; trunk 123–220 µm long, av. 171 µm, 7–8.5 µm broad, sometimes slightly swollen to up to 14 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 10–15.5 µm long, the shorter ones 6.5–10 µm long, with a ratio of the longer to the shorter ultimate branchlet of 1.3–1.85, base 2.5–3 µm broad, apex slightly sharp. Conidia ellipsoid with a grey to reddish colour, 20–25 µm long, 15–18.5 µm broad, length-to-breadth ratio 1.2–1.5. Oospores 36–44 µm in diameter. Habitat. Living leaves of Veronica triphyllos. Distribution. Austria, Germany. Additional specimens examined. AUSTRIA. Burgenland: District of Neusiedl am See, Municipality of Breitenbrunn, Tenauriegel, Weingarten, on living leaves of Veronica triphyllos, 21 Apr 2013, H. Voglmayr (WU-MYC 0032815); District of Neusiedl am See, Municipality of Winden, Hackelsberg S Jois, Annuellesflur at the summit, on living leaves of Veronica triphyllos, 13 Apr 2012, H. Voglmayr (WU-MYC 0032805); Lower Austria: District of Bruck / Leitha, Municipality of Prellenkirchen, Spitzerberg, S-Slope S Edelstal, Weingarten, on living leaves of Veronica triphyllos, 14 Apr 2012, H. Voglmayr (WU-MYC 0032806); District of Hollabrunn, Municipality of Retz, Oberalb, Roßberg, Neubergen, Weingarten, on living leaves of Veronica triphyllos, 27 Apr 2011, H. Voglmayr (WU-MYC 0032801); District of Tulln, Municipality of Fels am Wagram, Dorner S Gösing am Wagram, vineyards, on living leaves of Veronica triphyllos, 17 Apr 2012, H. Voglmayr (WU-MYC 0032808). Notes. Peronospora fidelia and P. gracilis differ only by two gaps in the ITS region and a single base difference in the LSU D 1–3 region, with no variation in the LSU D 6–8 region. However, significant and numerous base differences are observed in the four mitochondrial loci (COX 1, COX 2, NAD 1, and RPS 10). A similar pattern is found between Peronospora sp. on Veronica triloba and P. veronicae-cymbalariae on Veronica cymbalaria in this study. In both cases, nuclear loci do not offer sufficient resolution to effectively distinguish these species. This phenomenon has also been reported in previous studies (Choi et al. 2015 b), particularly in LSU regions, but is rarely seen in ITS. These findings highlight the importance of multi-locus approaches for accurate species identification (Choi et al. 2015 b). In the mitochondrial loci phylogenies, P. fidelia and P. gracilis are confirmed as sister species. Despite their close relationship and morphological similarities, P. gracilis differs from P. fidelia by having smaller and more globose conidia, 21 × 16.5 µm on average, with a length-to-breadth ratio of 1.25 ± 0.1, and shorter ultimate branchlets, the longer branchlets averaging 11 µm and the shorter ones 7.5 µm. Peronospora fidelia is also closely related to P. agrestis, but P. agrestis has smaller conidia, 21 × 16 µm on average, as well as longer conidiophores and trunks, averaging 334 µm and 200 µm, respectively.