Podosphaera filipendulensis Sanjay, Sanjeet & Raghv. Singh, 2021

Yadav, Sanjay, Verma, Sanjeet Kumar & Singh, Raghvendra, 2021, A new species of Podosphaera sect. Sphaerotheca subsect. Sphaerotheca from India-first report of powdery mildew causing wilting and ultimately death of leaves of Filipendula vestita, Phytotaxa 491 (2), pp. 131-142 : 137

Podosphaera filipendulensis Sanjay, Sanjeet & Raghv. Singh sp. nov. ( Figs. 1–4 )

MycoBank: MB 825553

Diagnosis:— Differs from P. filipendulae by its smaller peridium cells, aseptate, shorter and narrower appendages, and constant number of ascospores per ascus.

Type:— INDIA. Uttarakhand: Chamoli, Valley of Flowers National Park, 30° 43’ 59.99” N, 79° 37’ 59.99” E, on living leaves of Filipendula vestita (Wall. ex G. Don) Maxim. (Rosaceae) , September 2017, leg. Sanjay Yadav, AMH 9934 (holotype), MH-BHU 1 (isotype).

Etymology:— Latin, filipendulensis derived from the name of host genus.

Symptoms on leaves of host plant, conspicuous reddish to reddish brown circular spots (1–5 mm diam.) on upper surface, lower surface with brown to blackish brown powdery masses irregularly distributed with ascomata (cleistothecia),heavy infection initially causes wilting and drying, ultimately death of leaves. Cleistothecia hypophyllous, scattered or sometimes gregarious, often between leaf trichomes of host plant, globose, initially hyaline but dark brown to blackish brown at maturity, 76–99(–124) μm diam., cleistothecial cells conspicuous, pseudoparenchymatous, thick, semitransparent, close to each other and irregularly polygonal, 4–14.5 μm diam. Appendages mycelioid, arising perpendicular to the cleistothecial surface, scattered, and radially elongated outward, mostly distributed over entire surface, 4–25 per cleistothecium, unequal in length, (14–)35–101(–172) × 1.6–4.8 μm, length varying between 0.2–3.5 times the diameter of ascomata, smooth, with blunt apex, initially hyaline but upon maturity become pale brown throughout, aseptate, unbranched, thick-walled. Ascus single per cleistothecium, 71–93 × 60–89 μm, subglobose to ellipsoid, sessile, smooth, hyaline, with dense cytoplasmic contents, thick-walled (1.2–4.1 μm), 8-spored, 10–22 μm diam. of the thin-walled apical portion of the asci (oculi). Ascospores ellipsoid to ovoid, sometimes fusiform, hyaline to very rarely olivaceous, smooth, thin-walled (0.63–0.85 μm), aseptate, 17–25 × 10–16 μm.

Phylogenetic analysis clearly supports P. filipendulensis as an independent species ( Fig. 5 ). P. filipendulensis clustered together with P. ferruginea var. ferruginea (Schltdl.) U. Braun & S. Takam. and P. macularis (Wallr.) U. Braun & S. Takam. (ML = 76, BI = 0.89). The diagnostic morphological features of all species of Podosphaera sect. Sphaerotheca reported on Rosaceae is provided in Table 1.

Figures

FIGURE 1. Symptoms on Filipendula vestita a. Host plants in natural habitat. b. Wilting and drying symptom in upper younger leaves. c. Symptom on lower surface of leaf. d. Black cleistothecia on the lower surface of leaf. e. Symptom on upper surface of leaf. f. Heavily infected lower leaf surface. Scale bars: c, d = 5 mm, e = 10 mm, f = 5 mm.

FIGURE 2. Photographs of fruiting body of Podosphaera filipendulensis on the surface of infected leaf (AMH 9934, holotype) a. Cleistothecia (arrows) in between leaf trichomes. b–f. Cleistothecia with appendages. Scale bars: b, c = 60 μm, d = 30 μm, e = 25 μm, f = 30 μm.

FIGURE 3. Microphotographs of fruiting bodies of Podosphaera filipendulensis (AMH 9934, holotype) a. Initial stage of developing cleistothecium (homogenious cells). b. Mature cleistothecium. c. Pseudoparenchymatous nature of wall of cleistothecium. d–g. Ruptured cleistothecia each releasing an ascus. h, i. Appendages on the surface of cleistothecia. Scale bars: a = 25 μm, b = 40 μm, c = 20 μm, d = 50 μm, e = 40 μm, f, g = 30 μm, h, i = 20 μm.

FIGURE 4. Microphotographs of asci of Podosphaera filipendulensis (AMH 9934, holotype) a, b. Fully mature ascus. c, d. Ruptured asci releasing ascospores (arrows for ruptured oculi). e. Ascospores. Scale bars: a = 25 μm, b = 30 μm, c, d = 25 μm, e = 15 μm.

FIGURE 5. Phylogenetic analysis of the ITS region for 26 sequences from the genus Podosphaera and Cystotheca. Bootstrap values for ML above 50% and Bayesian posterior probabilities support above 0.50 are indicated. Sequence from the collection reported in this study is shown in red.