Four species of powdery mildews were found only in the anamorph stage on mature leaves of the host plants. The ITS sequences obtained in this study ranged between 570 and 680 bp. The phylogenetic analysis confirmed the species identification, whereas the relationships between the species were not the scope of the study. Based on anamorph morphology, host specificity, and identification with BLAST as well as ML analysis, three powdery mildews on medicinal plants are new records for Taiwan (Fig. 1), Arthrocladiella mougeotii on Lycium chinense, Erysiphe lespedezae on Uraria crinita, and E. lonicerae on Lonicera japonica. Eryngium foetidum is a new host for Erysiphe heraclei hitherto known on other host plants in Taiwan. Eryngium foetidum and Uraria crinita are new host plants for powdery mildews worldwide. The pathogens did not cause death of the host plants, but appeared to enhance stress by colonizing mature leaves. The fungi were only found on specifically mycologically collected specimens in the field, but not among over 80 plant herbarium specimens collected during the last 100 years in Taiwan. A documentation of the morphological and molecular identification of the four powdery mildew species is given below.
Arthrocladiella mougeotii (Lév.) Vassilkov Fig. 2
Colonies amphigenous on leaves. Hyphae smooth, 5–6 µm wide. Hyphal appressoria mostly solitary, nipple-shaped. Conidiophores arising solitarily from middle of hyphal mother cell, slightly constricted at base, composed of foot cell and 1–4 distal cells, (53–)62–89(–109) x (8–)9–11 µm. Foot cell with basal septum at same level as upper surface of supporting hypha, straight or curved, (33–)37–52(–60) x (8–)9–11 µm. Conidia catenate, ellipsoid-ovoid to doliiform, (25–)27–32(–35) x (10–)11–13(–15) µm, germination by forming long hyphae close to one of both ends of the conidium.
Specimens examined. On leaves of Lycium chinense Mill. (Solanaceae). Taipei City, Zhongzheng District, sidewalk near MRT Taipower Building Station, ca. 25.020751, 121.528368, ca. 15 m, 27 Apr 2020, AKII 0082 (TNM), ITS sequence GenBank MT703830; Taipei City, Daan District, Taipei, National Taiwan University campus, Zhoushan Road, 23 Apr 2015, not preserved (Fig. 2a).
Notes. The ITS sequence was identical 100% identical to over ten published ones exceeding 590 bp of Arthrocladiella mougeotii in GenBank. Arthrocladiella mougeotii is the single species of its genus and is almost globally distributed and limited to Lycium hosts (Braun and Cook 2012). In contrast to Farr and Rossman (2020) who list several powdery mildew species for Lycium species, only A. mougeotii and Phyllactinia chubutiana Havryl., S. Takam. & U. Braun are accepted for Lycium hosts in Braun and Cook (2012). Both fungi can be distinguished not only by different ITS sequences, but also the solitary conidia in Ph. chubutiana and catenate conidia in A. mougeotii.
Erysiphe heraclei DC. Figure 3
Colonies amphigenous on leaves. Hyphae smooth, 4–7 µm wide. Hyphal appressoria solitary or in opposite pairs, nipple-shaped or lobed. Conidiophores arising solitarily from middle of hyphal mother cell, slightly curved at base, (56–)68–105(–117) x (6–)7–8(–9) µm. Foot cell with basal septum at same level as upper surface of supporting hypha or slightly elevated up to 9 µm, straight or curved, (32–)38–49(–52) x (6–)7–8(–9) µm, followed by 1–4 cells. Conidia solitary, ellipsoid-ovoid to cylindrical, (34–)35–45(–51) x (11–)12–17(–19) µm, germination from one of both ends by forming long hypha with nipple-shaped or lobed appressoria.
Specimen examined. On leaves of Eryngium foetidum L. (Apiaceae). Taipei City, Daan District, Changhsin Street, National Taiwan University dormitories, ca. 25.015449, 121.546735, ca. 20 m, 24 May 2019, R. Kirschner 4729 (TNM), ITS sequence GenBank MT703849 .
Notes. There was 99% ITS sequence identity with 1 to 6 different bp between our specimen and over ten other published specimens labeled as E. heraclei in GenBank. Presently, it is not possible to distinguish between E. betae (Vaňha) Weltzien, E. heraclei, and E. malvae V.P. Heluta based on rDNA sequences (Takamatsu et al. 2015a). The three species are hardly distinguishable also in morphology (Braun and Cook 2012). Future study may reveal whether the species can be separated with additional markers or need to be put into synonymy. In this case, E. heraclei would have priority since it is the oldest available name.
Erysiphe lespedezae R.Y. Zheng & U. Braun Fig. 4
Colonies amphigenous on leaves. Hyphae smooth, 3–6 µm wide. Hyphal appressoria mostly solitary, nipple-shaped or lobed. Conidiophores arising solitarily from middle of hyphal mother cell, slightly curved and rough at base, composed of foot cell and 1–4 distal cells. Foot cell with basal septum at same level as upper surface of supporting hypha, straight or curved, (35–)45–78(–115) x (4–)5–6(–8) µm. Conidia solitary, ellipsoid-ovoid to doliiform, (24–)26–34(–40) x (12–)14–17(–19) µm, germination terminal.
Specimens examined. On leaves of Uraria crinita (L.) Desv. ex DC. (Fabaceae). Miaoli County, Touwu Township, Lavender Cottage, ca. 24.587072, 120.896818, ca. 80 m, 09 Nov 2018, AKII 0005 (TNM), ITS sequence GenBank MT703848; Taipei City, Shilin District, Medicinal Botanical Garden, 25.115751, 121.576885, ca. 220 m, 12 Nov 2018, AKII 0006 (TNM).
Notes. When ITS sequences exceeding 570 bp were compared, there was 99% identity with 2 to 5 different bp between our specimen and seven published specimens labeled as E. lespedezae in GenBank, whereas the identity with other specimens were 98% or lower, with more than 5 different bp. Uraria species have not yet been recorded as hosts of powdery mildews worldwide (Braun and Cook 2012, Farr and Rossman 2020). The foot cell of conidiophores was longer [(35–)45–78(–115) µm] than reported in Braun and Cook (2012: about 20–40 µm long), but Meeboon & Takamatsu (2017a) also reported longer foot cells (35–65 µm) for this species. Some species of Erysiphales on Fabaceae presently lacking DNA, such as Pseudoidium bauhiniae (G.J.M. Gorter & Eicker) U. Braun & R.T.A. Cook and Ps. caesalpiniacearum (Hosag. & U. Braun) U. Braun & R.T.A. Cook may require restudy for clarifying the species boundaries of E. lespedezae.
Erysiphe lonicerae DC. Figure 5
Colonies amphigenous on green leaves. Hyphae verruculose, 3–6 µm wide. Hyphal appressoria mostly single, rarely in opposite pairs, nipple-shaped, lobed or elongated. Conidiophores arising solitarily from middle of hyphal mother cell, straight or curved at base (only in one case curvature formed in cell distal to foot cell), cylindrico-clavate, verruculose, composed of foot cell and 1–3 distal cells, (55–)79–120(–140) x (7–)9–12(–14) µm. Foot cell with basal septum at same level as upper surface of supporting hypha, cylindrical, straight or curved, (20–)37–51(–60) x 5–6.5(–7) µm. Conidia solitary, oblong to short cylindrical, smooth-walled when fully turgescent, wall becoming reticulate by aging, (31–)32–40(–44) x (13–)15–18.5(–20) µm, germinating apically into a short hypha with lobed appressoria.
Specimens examined. On mature leaves of Lonicera japonica Thunb. (Caprifoliaceae). New Taipei City, Shenkeng District, near City Highway 106B, ca. 24.999115, 121.620617, ca. 50 m, 07 Apr 2019, R. Kirschner 4712 (TNM), ITS sequence GenBank MT703799; Taipei City, Daan District, National Taiwan University, near post office, 25.018563, 121.537213, ca. 15 m, 31 May 2019, R. Kirschner 4733 (TNM); Taipei City, Shilin District, Medicinal Botanical Garden, 25.115751, 121.576885, ca. 220 m, 30 Oct 2014, R. Kirschner & W.-A. Liu 4112 (TNM).
Notes. When ITS sequences exceeding 600 bp were compared, there was 99% identity with 1 to 4 different bp between our specimen and seven published specimens labeled as E. lonicerae in GenBank, whereas the identity with other species was 98% or lower, with more than 10 different bp. Erysiphe lonicerae is known on different Lonicera species in Europe and East Asia (mainland China, Korea, Japan) and is a new record for Taiwan (Farr and Rossman 2020). Information about conidiophore morphology and DNA sequences do not exist, however, for two other Erysiphe species on Lonicera hosts in East Asia, namely E. lonicerae-ramosissimae (Tanda) U. Braun & Takam. and E. miurae (U. Braun) U. Braun & Takam. These data are also lacking for, E. magnusii (S. Blumer) U. Braun & Takam. reported from Europe and Central Asia, and for E. caprifoliacearum (U. Braun) U. Braun & Takam. in America (Braun and Cook 2012).