Taxonomic revision of Blumeria based on multi-gene DNA sequences, host preferences and morphology

Abstract

A taxonomic revision of the hitherto monotypic genus Blumeria was conducted incorporating multi-gene sequence analyses, host preference data and morphological criteria. The sequenced loci included rDNA ITS, partial chitin synthase gene (CHS1), as well as fragments of two unnamed orthologous genes (Bgt-1929, Bgt-4572). The combined evidence led to a reassessment and a new neotypification of B. graminiss. str. (emend.), and the description of seven additional species, viz. B. americana sp. nov. (mainly on hosts of the Triticeae), B. avenae sp. nov. (on Avena spp.), B. bromi-cathartici sp. nov. (on Bromus catharticus), B. bulbigera comb. nov. (on Bromus spp.), B. dactylidis sp. nov. (on Dactylis glomerata as the main host, but also on various other hosts), B. graminicola sp. nov. (on Poa spp. as principal hosts, but also on various other hosts), and B. hordei sp. nov. (on Hordeum spp.). Synonyms were assessed, some were lectotypified, and questionable names previously associated with powdery mildew on monocots were discussed although their identities remained unresolved. Keys to the described species were developed.

Keywords: Ascomycota; E3 ubiquitin­protein ligase; Poaceae; typification; unnamed orthologous genes.

Fig. 1 -. Phylogeny of Blumeria graminis s.lat. inferred from concatenated sequences of rDNA-ITS, CHS1, and two hypothetic protein loci (Bgt-1929, Bgt-4572). Taxon labels include voucher numbers, host name, and country codes (ARG Argentina, CAN Canada, CHE Switzerland, CZE Czech Republic, UK England, FIN Finland, DEU Germany, IRN Iran, ISR Israel, JPN Japan, MEX Mexico, RUS Russia, UKR Ukraine, USA United States); superscript EET stands for ex-epitype, EHT ex-holotype, ENT ex-neotype; values on branches are parsimony bootstrapping value (bp)/Bayesian posterior probability (pp), ~ indicates either bp <70 or pp <0.9. Sequences of taxa in grey font were downloaded from GenBank. Tribes (and subtribes for B. avenae and B. dactylidis) of principal hosts were noted under the species names in parentheses.

Fig. 2 -. Blumeria graminis s.str. A: Infected leaf surface with primary mycelia and conidiophores (DAOM 225780, asexual stage on the left), and secondary mycelia and chasmothecia (DAOM 74558, sexual stage on the right); B: Close-up of chasmothecia and secondary mycelia (DAOM 74558); C: A branched secondary hypha with basal septa (arrows, DAOM 74558); D: Conidiophore singly arising from mother cell (DAOM 225780, DAOM 161299); E: Asci ellipsoid or ovoid, with or without a stalk (DAOM 74558); F: Conidia, arrow shows germ tube (DAOM 225780); G: Hyphal appressoria (DAOM 225780, DAOM 161299); H: A secondary hypha unbranched, with one septum at the base (arrow, DAOM 74558); I: SEM of conidium apical wall thickened (on the left, DAOM 225780) and un-thickened (on the right, DAOM 161299). Bars: A 0.5 mm; B 100 μm; C–H 20 μm; I 2 μm.

Fig. 3 -. Blumeria americana sp. nov. A: Infected leaf adaxial (left) and abaxial surfaces (DAOM 156886) showing asexual stage; B:Infected leaf with sexual stage (DAOM 145059); C: Close-up of chasmothecia imbedded in secondary hyphae (DAOM 145059); D: Asci clavate, ellipsoid, ovoid with a sinuous or branched stalk (DAOM 137541); E: Aseptate secondary hyphae with narrow lumen; F: Young conidiophores arising from mother cells singly (top, DAOM 217856, DAOM 156886) or in pairs (bottom, DAOM 156886); G: Branched foot-cells (DAOM 186037); H: Mature conidiophores and conidia (DAOM 217856); I: Hyphal appressoria of various shapes; J: SEM view of conidia with scale-like artifacts on the surface and a thickened patch at apex (DAOM 217856). Bars: A, B 1 mm; C 100 μm; D 50 μm; E–I 20 μm; J 5 μm (including inset).

Fig. 4 -. Blumeria avenae sp. nov. A: Various stages of infection on the leaf surface with light orange to brownish mycelia (DAOM 236220, 147852); B: Close-up of conidiophores on leaf surface (DAOM 236220); C: Conidia, note two with germ tubes at or near apices (DAOM 236220, 147852, arrows); D: Appressoria nipple-shaped (DAOM 236220, 147852), single or in opposite pairs; E–F: Single conidiophore arising from mother cell, the septum between mother cell and foot cell elevated severely (E, DAOM 236220, arrow) or slightly (F, DAOM 147852); G: Two conidiophores arising from mother cell in pairs (DAOM 236220); H: A cluster of conidiophores arising from irregular shaped mother cells (DAOM 236220); I: SEM close up apical wall of conidia. Bars: A 0.5 mm; B 100 μm; C–H 20 μm; I 2 µm.

Fig. 5 -. Blumeria bromi-cathartici sp. nov. (TNS-F87248 = MUMH 0117). A: Infection on leaf surface showing light yellow to orange primary mycelia and conidiophores; B: Close-up ofconidiophores on leaf surface; C: Hypha branching at a narrow angle, and hyphal appressoria nipple-shaped and single; D–E: Conidiophores at different developing stages singly arising from mother cell; F: Primary conidia mostlyoblong; G: Blumeria-type germination of a conidium; H: SEM view of apical walls. Bars: A 0.5 mm; B 100 μm; C–G 20 μm; H 2 µm.

Fig.6 –. Blumeria bulbigera comb. nov. A: Infection on adaxial leaf surface showing yellow primary mycelia and conidiophores (DAOM 82541); B: White secondary mycelia and chasmothecia produced on adaxial leaf surface (GLM-F54349); C: Exposed disk-shaped chasmothecia with deep depression on upper surfaces (GLM-F54349); D: Asci with cylindrical stalk (GLM-F54349); E: Conidiophore arising singly from irregular mother cell (DAOM 82541); F: Nipple-shaped appressoria arising singly or in opposite pairs, ovoid swelling at the end or middle of hyphae (see arrows, DAOM 82541, GLM-F62360); G: Conidia of subglobose, ovoid, oblong, and lime-shaped, germ tubes produced near the apices (DAOM 82541, GLM-F62360); H: Secondary hypha with several septa (see arrows, GLM-F54349), I: SEM view of conidia; J: Apical wall of conidia (DAOM 82541). Bars: A–C 100 μm; D–H 20 μm; I 5 μm; J 2 µm.

Fig. 7 -. Blumeria dactylidis sp. nov. A: Infection on adaxial leaf surface showing brown primarymycelia and conidia production (left, DAOM 91654), and on abaxial leaf surfaceshowing greyish white secondary mycelia and chasmothecia (right, GLM-F50119); B:Close-up of conidia chains (DAOM 118220); C: Chasmothecium side view (upper)and overview (lower) showing the deep depression at the upper surface and thesurrounding white secondary mycelia (GLM-F79570); D: Secondary hyphae aseptateand unbranched (GLM-F50119); E: Appressoria in nipple and lobe shapes (DAOM91654, 118220); F–H showing one conidiophore per mother cell (DAOM 91654): F:Conidiophore with elevated septum between mother cell and foot cell, G: Youngfoot cell, H: Conidiophore with slightly elevated septum between the mother celland foot cell; I: Conidia, producing one or two germ tubes (DAOM 91654, DAOM118220, arrows); J: Asci with a slightly protruding stalk (GLM-F79570); K: SEM view of apical wall of conidiaun-thickened. Bars: A 0.5 mm; B, C 100 μm; D–J 20 μm; K 2 μm.

Fig. 8 -. Blumeria graminicola sp. nov. A: Chasmothecia covered with white secondary hyphae oninfected leaf surface (DAOM 179493); B: Primary hyphae and conidia (arrow)co-exist with secondary hyphae and chasmothecium (DAOM 159510); C: Filiform appendages of chasmothecium with a septum at the base or near base (arrows,DAOM 159510); D: Asci subglobose, or ovoid with an unbranched short stalk (DAOM159510); E: Secondary hyphae with septa (arrow, DAOM 179493); F: Single conidiophore arising from one mother cell (DAOM 159510); G: Hyphal appressoria(DAOM 181460, DAOM 91194); H: Two conidiophores arising from one mother cell,and branched foot-cell (arrows, DAOM 179493, DAOM 159510); I: Conidia, note oneconidium producing a germ-tube; J: SEM view of scale-like artifacts on surfaceof conidia, thickened apical wall with depressed center (DAOM 24040); K:Close-up of apical wall of conidia (DAOM 91194). Bars: A 0.5 mm; B 100 μm; C–I 20 μm; J 5 μm; K 1 μm.

Fig. 9 -. Blumeria hordei sp. nov. (A–F DAOM 18154, G–I GLM-F99595 and DAOM 18154). A: Chasmothecia embedded in greyish to brownish secondary mycelia, developed simultaneously with deeper colored primary mycelia and conidia (arrow, DAOM 18154); B: Close-upof brownish conidial chains; C: Clavate or ovoid asci with wiggly stalks; D:Two conidiophores arising from single mother cell; E: Conidiophores arising singly from mother cells; F: Secondary hyphae arising from primary hyphae withone septum at the base; G: Conidia, mostly with round ends compared withpointed ends (i.e. B. graminicola Fig. 8 I); H: Nipple shaped appressoria mostly in pairs; I: SEM close-up of apical wall of conidia. Bars: A 0.5 mm; B 100 μm; C–H 20 μm; I 5 µm.