Single Ascus Research Articles

First Report of Powdery Mildew Caused by Podosphaera xanthii on Salvia farinacea in Korea.

Salvia farinacea Benth. (Lamiaceae) is an herbaceous perennial plant, native to Mexico and southern parts of the United States. This plant is cultivated worldwide for its ornamental value. In November 2019, hundreds of S. farinacea 'Blue Bedder" grown in a flower garden in Jeju (33°30'57"N 126°32'50"E), Korea have been found to be infected with a powdery mildew fungus. The disease severity was estimated to be 100%. Likewise in October 2020, a similar situation with this plant was also observed in a flower garden in Seoul (37°35'19"N 127°01'07"E), Korea. Leaves, stems and inflorescence of plants were covered by white, thin mycelial felt, bearing an abundance of conidiophores and conidia. Eventually, infected plants lose their ornamental value. Two voucher specimens have been deposited in the Korea University Herbarium (KUS-F31478 and F32164). Fresh materials were examined. Hyphal appressoria were nipple-shaped, but rarely found. Conidiophores (n = 30) were straight, 95 to 160 × 10 to 12 μm and produced 2 to 7 immature conidia in chains with a crenate outline. Foot-cells were cylindric and 36 to 60 μm long. Conidia (n = 30) were ellipsoid-ovoid to barrel-shaped, 32 to 38 × 18 to 24 μm, and contained conspicuous fibrosin bodies. Dark brown chasmothecia were found partly embedded in the mycelial felt on leaves, mostly hypophyllous, spherical, and 82 to 100 µm diameter, with a single ascus in each. Appendages were few, mycelioid, 1- to 4-septate, brown near the base when mature, but paler above. Asci were broadly ellipsoid to subglobose, 56 to 68 × 50 to 62 μm, sessile and 8-spored. Ascospores were colorless, oval to subglobose, and 14 to 18 × 12 to 15 µm. These characteristics were consistent with those of Podosphaera xanthii (Castagne) U. Braun & Shishkoff (Braun and Cook 2012). For further confirmation, genomic DNA was extracted from chasmothecia from KUS-F31478 and F32164. PCR amplification was performed using the primer pair ITS1F/PM6 for internal transcribed spacer (ITS) and PM3/TW14 for the large subunit (LSU) of the rDNA (Takamatsu and Kano 2001). Obtained sequences were deposited to the GenBank under the accession numbers MZ359847 and MZ359859 for ITS, MZ359858 and MZ359861 for LSU. For ITS regions 99.80-100% similarity was found with sequences MT131256 (Salvia farinacea), MT131254 (Mazus pumilus) and MT131252 (Erigeron bellioides) of P. xanthii, whereas it was 99.90% with sequences of this fungus on Echinacea purpurea (MT826247 and MT826245) for 28S rDNA gene. Pathogenicity tests were carried out by touching an infected leaf onto healthy leaves of disease-free 30 days old potted 'Blue Bedder' using replication of five plants, with five non-inoculated plants used as controls. The typical signs of powdery mildew started to develop on the inoculated leaves in 7 to 10 days, and microscopic examination revealed the morphological identity with the fungus observed from the field. All non-inoculated control plants remained symptomless. Hitherto Golovinomyces powdery mildews on Salvia spp. were reported globally (Farr and Rossman 2021). However, Podosphaera elsholtziae on Salvia sp. and P. xanthii on S. farinacea were reported from China and Taiwan (Zheng and Yu 1987, Yeh et al. 2021). To our knowledge, this is the first report of P. xanthii on S. farinacea in Korea. The occurrence of Podosphaera powdery mildew on S. farinacea could pose a serious threat to the beauty of this plant, causing premature senescence of young leaves and gray to purplish discoloration of the leaves.

Lager Yeast Design Through Meiotic Segregation of a Saccharomyces cerevisiae × Saccharomyces eubayanus Hybrid.

Yeasts in the lager brewing group are closely related and consequently do not exhibit significant genetic variability. Here, an artificial Saccharomyces cerevisiae × Saccharomyces eubayanus tetraploid interspecies hybrid was created by rare mating, and its ability to sporulate and produce viable gametes was exploited to generate phenotypic diversity. Four spore clones obtained from a single ascus were isolated, and their brewing-relevant phenotypes were assessed. These F1 spore clones were found to differ with respect to fermentation performance under lager brewing conditions (15°C, 15 °Plato), production of volatile aroma compounds, flocculation potential and temperature tolerance. One spore clone, selected for its rapid fermentation and acetate ester production was sporulated to produce an F2 generation, again comprised of four spore clones from a single ascus. Again, phenotypic diversity was introduced. In two of these F2 clones, the fermentation performance was maintained and acetate ester production was improved relative to the F1 parent and the original hybrid strain. Strains also performed well in comparison to a commercial lager yeast strain. Spore clones varied in ploidy and chromosome copy numbers, and faster wort fermentation was observed in strains with a higher ploidy. An F2 spore clone was also subjected to 10 consecutive wort fermentations, and single cells were isolated from the resulting yeast slurry. These isolates also exhibited variable fermentation performance and chromosome copy numbers, highlighting the instability of polyploid interspecific hybrids. These results demonstrate the value of this natural approach to increase the phenotypic diversity of lager brewing yeast strains.

Morphological characterization and epidemiological studies of summer squash (Cucurbita pepo) powdery mildew

Samples of powdery mildew of summer squash (Cucurbita pepo L.) collected from Solan, Shimla, Hamirpur and Kinnaur districts of Himachal Pradesh during 2017-18 revealed the presence of anamorphs, whereas the cool and dry temperate region of district Kinnaur showed the occurrence of both teleomorphic and anamorphic stages of powdery mildew on summer squash. Present studies constitute the first report of cleistothecial occurrence on summer squash under Indian conditions. Based on anamorphic characters like ellipsoidal conidia, presence of fibrosin bodies and germinating conidia produced both simple and forked germ tubes without appressorium and teleomorphic characters like cleistothecia with myceloid appendages, single ascus with eight ascospores the associated pathogen was identified as Sphaerotheca fuliginea (Schlecht.) Pollaci. Maximum conidial germination was observed at 25° temperature and 100% relative humidity. The development of powdery mildew disease was significantly favored at moderate temperature coupled with high relative humidity and cumulative rainfall.

First report of powdery mildew caused by Podosphaera xanthii on New Guinea impatiens in Korea

From August to November 2020, a previously unseen powdery mildew disease was encountered repeatedly on New Guinea impatiens (Impatiens hawkeri, syn. Impatiens ‘New Guinea’ hybrid) in Uijeongbu, Korea. It occurred on plants growing in partial shade along high buildings or walls, but not on those planted in sunny gardens. Symptoms included white, effuse, amphigenous mycelial patches on leaves and stems, reducing the aesthetic value of plants (Fig. 1). Microscopic examination of freshly collected leaves revealed the following morphological characteristics: upright conidiophores (110–210 × 10–12 μm) producing 2 to 5 catenescent conidia, and ellipsoid to doliiform conidia (26–38 × 16–22 μm) containing conspicuous fibrosin bodies. In autumn, scattered chasmothecia were found on leaves, mainly on the lower surface (Figs. 2–3). These measured 80–100 μm in diameter, had mycelioid appendages, and contained a single ascus with 8 ellipsoid to ovoid ascospores (16–20 × 12–16 μm) (Fig. 4). These characteristics were consistent with the description of Podosphaera xanthii in Braun & Cook (2012). To confirm the morphology-based determination, genomic DNA was extracted from a representative specimen (KUS-F32140, Korea University herbarium, Seoul, Korea). PCR products were amplified using the primer sets ITS1F/PM6 for the internal transcribed spacer (ITS) and PM3/TW14 for the large subunit (LSU) of rDNA (Takamatsu & Kano, 2001). The sequences obtained in this study (GenBank Accession Nos. MW750225 (ITS) and MW750226 (LSU)) were compared with other sequences in GenBank using BLASTn. The analysis showed 100% identity with other P. xanthii sequences (e.g., AB462799, AB462803 for ITS, and MT919354, LC371331 for LSU) and neighbour-joining analysis of ITS sequences placed the Korean isolate in a well-supported clade with the reference sequences of P. xanthii (Fig. 5). Podosphaera (previously Sphaerotheca) powdery mildews on Impatiens spp. have been previously assigned to P. balsaminae (Braun & Cook, 2012; Farr & Rossman, 2021). However, P. balsaminae was shown to be limited to the Asian materials of Podosphaera on I. noli-tangere (Ito & Takamatsu, 2010). The remainder of Podosphaera powdery mildews on Impatiens spp. were proved to belong to or were tentatively assigned to the P. xanthii complex (Braun & Cook, 2012). Podosphaera powdery mildews on New Guinea impatiens seem to be uncommon considering the world-wide cultivation of the host as a potted and garden plant. Previously, Wolcan (2004) recorded P. balsaminae on I. hawkeri from Argentina, and Garibaldi et al. (2012) recorded Podospahera sp. on I. hawkeri from Italy. We prove here that the earlier collection from Italy also represents P. xanthii (Figure 5). To our knowledge, this is the first confirmed report of powdery mildew caused by P. xanthii on New Guinea impatiens. This finding could be useful for the breeding programme of Impatiens spp. and future plantings of New Guinea impatiens in gardens. This work was supported by Korea IPET through Crop Viruses and Pests Response Industry Technology Development Program, funded by MAFRA.

FIRST REPORT OF POWDERY MILDEW CAUSED BY CYSTOTHECA LANESTRIS ON QUERCUS CRASSIPES IN MEXICO

Red oak or Tuchi (Quercus crassipes) is an ornamental endemic species of Mexico. On November 9, 2016, powdery mildew was observed on leaves of Tuchi in Santa Fe, Mexico City. The symptoms and signs included deformed leaves, irregular necrotic lesions on both sides of the leaf, premature leaf drop, chasmothecia and mycelium. A reference specimen (CMPH-ECO23S) was deposited in the Herbarium of the Colegio de Postgraduados. The fungus produced light brown to dark reddish chasmothecia immersed in the mycelium. Chasmothecia were grouped or dispersed, 99-111 µm in diameter, composed of polygonal peridial cells of 12-18 µm; with simple, sinuous, poorly developed, short, or almost absent mycelial appendages (4-4.5 µm wide) that were interlaced with the surrounding mycelium. The single ascus was hyaline, ellipsoid or ovoid to globose, sessile, 80-91 x 55-68 µm to 134 x 85 µm. The ascospores were hyaline, ellipsoid to ovoid, 25-32 x 18-22 µm. Conidiophores and conidia were not observed. Amplification of ITS was carried out using primers ITS4 and ITS5. The PCR product (459 bp) was sequenced and deposited in GenBank (accession No. MF170000). The obtained sequence showed 100% similarity to AF011289 from Q. agrifolia. No extype sequence of C. lanestris is in GenBank, but the type and this sequence are from Q. agrifolia in California, USA. Based on morphological and molecular characteristics, the fungus observed on Quercus crassipes was identified as Cystotheca lanestris (Braun and Cook, 2012). To our knowledge, this is the first report of this fungus causing powdery mildew of red oak in Mexico.

First Report of Powdery Mildew Podoshaera tridactyla on Prunus hypoleuca in China.

Prunus hypoleuca (≡ Maddenia hypoleuca), a native plant in China, grows in the Qinling Mountains that lie at the intersection of several forest regions in north, central, and southwest China. In October 2013, P. hypoleuca suffering from heavy powdery mildew infections was found with approximately 75% of the plants affected. The powdery mildew at first appeared as circular to irregular white patches, which subsequently showed abundant hyphal growth on both sides of leaves, leading to the withering of the leaves. A voucher specimen was maintained in the Mycological Herbarium of Northwest A & F University (Accession No. HMNWAFU-CF 2013166). Hyphal appressoria were nipple-shaped or nearly absent. Conidiophores were cylindrical, measured 83 to 110 × 10 to 12.5 μm, and produced two to five immature conidia in chains with a crenate outline. Foot-cells of conidiophores were straight, cylindrical, and 28 to 62 × 7 to 10 μm. Conidia were hyaline, ellipsoid to ovate, and measured 20 to 32 × 14 to 21 μm (length/width ratio 1.4:1.8). Chasmothecia were scattered or gregarious, depressed globose, and 65 to 112 μm in diameter. Appendages, arising from the upper half of the chasmothecia, usually had two to four dichotomous branches, and were one to three and a half times as long as the chasmothecial diameter. A single ascus in a chasmothecium was subglobose or broadly ellipsoid-ovoid, measured 66 to 86 × 47 to 76 μm and contained six to eight ascospores. The ascospores were ellipsoid-ovoid and 15 to 27 × 12 to 18 μm. The fungus was identified as Podosphaera tridactyla based on its anamorph and teleomorph characteristics (1,2). To confirm the identification, 28S rDNA and the ITS region were amplified. The ITS5/P3 and then PM5/ITS4 primers were used to amplify the ITS region by nested PCR. The primers LSU1/LSU2 were used to amplify the 28S rDNA, and the cloned fragments were sequenced. The 28S rDNA and ITS region sequences were deposited in GenBank (Accession Nos. KJ879240 and KM213121). A GenBank BLAST search of two sequences revealed 99% identity with P. tridactyla infecting Prunus salicina Lindl. in Korea (3). Based on ITS and a 28S rDNA phylogenetic tree, the two sequences retrieved from the Chinese specimen clustered within a strongly supported clade (bootstrap value = 100%) with P. tridactyla (JQ517296 and AB022393, respectively). Cladistic trees were constructed using the neighbor-joining method with the Kimura two-parameter substitution model in MEGA 5.0. Branch robustness was assessed via bootstrap analysis with 1,000 replicates. Phylogenetic analysis data were in agreement with morphological characters (3). To our knowledge, this is the first report of powdery mildew caused by P. tridactyla on P. hypoleuca. While Koch's postulates have not been carried out because of the biotrophic nature of the pathogen, the present report serves as a novel resource in order to improve the understanding of the etiology and epidemiology of the powdery mildew (P. tridactyla) on P. hypoleuca. The occurrence of P. tridactyla, a common powdery mildew on Prunus s. lat., supports recently published results of phylogenetic analyses of the Prunus complex, indicating that Maddenia must be reduced to synonymy with Prunus (4).

The status of Myriangiaceae (Dothideomycetes)

The family Myriangiaceae is relatively poorly known amongst the Dothideomycetes and includes genera which are saprobic, epiphytic and parasitic on the bark, leaves and branches of various plants. The family has not undergone any recent revision, however, molecular data has shown it to be a well-resolved family closely linked to Elsinoaceae in Myriangiales. Both morphological and molecular characters indicate that Elsinoaceae differs from Myriangiaceae. In Elsinoaceae, small numbers of asci form in locules in light coloured pseudostromata, which form typical scab-like blemishes on leaf or fruit surfaces. The coelomycetous, “Sphaceloma”-like asexual state of Elsinoaceae, form more frequently than the sexual state; conidiogenesis is phialidic and conidia are 1-celled and hyaline. In Myriangiaceae, locules with single asci are scattered in a superficial, coriaceous to sub-carbonaceous, black ascostromata and do not form scab-like blemishes. No asexual state is known. In this study, we revisit the family Myriangiaceae, and accept ten genera, providing descriptions and discussion on the generic types of Anhellia, Ascostratum, Butleria, Dictyocyclus, Diplotheca, Eurytheca, Hemimyriangium, Micularia, Myriangium and Zukaliopsis. The genera of Myriangiaceae are compared and contrasted. Myriangium duriaei is the type species of the family, while Diplotheca is similar and may possibly be congeneric. The placement of Anhellia in Myriangiaceae is supported by morphological and molecular data. Because of similarities with Myriangium, Ascostratum (A. insigne), Butleria (B. inaghatahani), Dictyocyclus (D. hydrangea), Eurytheca (E. trinitensis), Hemimyriangium (H. betulae), Micularia (M. merremiae) and Zukaliopsis (Z. amazonica) are placed in Myriangiaceae. Molecular sequence data from fresh collections is required to confirm the relationships and placement of the genera in this family.

A re-assessment of Elsinoaceae (Myriangiales, Dothideomycetes)

The family Elsinoaceae is a relatively poorly known, but important family within Myriangiales, Dothideomycetes. The genera of this family are mostly plant pathogens and causes disease, such as apple and grape scab. In this paper we revisit the family by examining generic types and analysis of molecular sequence data available in GenBank. Elsinoaceae and Myriangeaceae are morphologically and phylogenetically well-supported families in Myriangiales. In Elsinoaceae, 3 to 10 asci form in locules in light coloured pseudoascostromata, which form typical scab-like blemishes on leaf or fruit surfaces, while Myriangeaceae forms raised, superficial, black ascostromata with single asci in each locule, genera may or may not form scab-like lesions. Elsinoe is the type of the family Elsinoaceae and is characterized by forming scab-like blemishes on leaves with few to numerous bitunicate, fissitunicate, globose asci forming inside each locule with a pseudoascostroma containing fungal and host tissues. Following examination of generic type material, Molleriella is retained in Elsinoaceae as it has characters similar to Elsinoe in forming scab-like lesions with pseudoascostromata containing few to numerous bitunicate asci inside each locule. Beelia, Butleria, Hemimyriangium, Hyalotheles, Micularia, Saccardinula, Stephanatheca and Xenodium are excluded from Elsinoaceae and their relative placement in Dothideomycetes is discussed. Fresh collections of these genera are needed so that molecular sequence data can be obtained and analysed to resolve their placement in families or orders of Dothidoemycetes.

First Report of Powdery Mildew Caused by Cystotheca wrightii on Quercus glauca in Korea.

Quercus glauca Thunb. (syn. Cyclobalanopsis glauca (Thunb.) Oerst.), known as ring-cupped oak or Japanese blue oak, is a dominant tree species commonly found in evergreen forests in East Asia (2). In May 2012, hundreds of Q. glauca were found heavily affected by a powdery mildew in several locations of Jeju Islands, Korea. Symptoms on overwintered leaves appeared as circular to irregular blackish violet to dark brown felt-like growths with numerous chasmothecia on abaxial leaf surfaces. New infections on current-year leaves started in early summer and were characterized by typical white patches with abundant sporulation on abaxial leaf surfaces. In early autumn, with formation of special aerial hyphae and without further sporulation, the patches turned light brown to brown. Formation of chasmothecia was noticed from late autumn. The adaxial leaf surface was free of powdery mildew growths and exhibited yellowing and discoloration. Voucher specimens were deposited in the Korea University Herbarium (KUS). Special aerial hyphae were falcate to curved, aseptate, at first hyaline, later deep brown to purplish brown, thick-walled, and 80 to 140 × 6 to 15 μm. Conidiophores were 175 to 245 × 10 to 12 μm, and produced 2 to 4 immature conidia in chains with a sinuate outline. Foot-cells of conidiophores were cylindrical and 80 to 120 μm long. Conidia were lemon- to barrel-shaped, 26 to 35 × 17 to 24 μm with a length/width ratio of 1.2 to 1.6, and devoid of fibrosin bodies. Primary conidia were apically conical and basally subtruncate. Germ tubes produced in the lateral to perihilar position of conidia were long and slender (3 μm wide). Chasmothecia were scattered or gregarious, partly embedded with special aerial hyphae, dark brown, spherical, 55 to 70 μm in diameter, and contained a single ascus. Chasmothecial peridia consisted of two layers. Exoperidia (outer layer) were composed of dark brown, polygonal cells 10 to 20 μm wide. Endoperidia (inner layer) consisted of hyaline, polygonal cells 10 to 15 μm wide. Appendages were basally attached, mycelioid, rare or few, and pale brown to rusty brown. Asci were short stalked, 55 to 72 × 35 to 46 μm, had a terminal oculus 10 to 20 μm wide, and contained 8 ascospores. Ascospores were oblong-elliptical, 22 to 27 × 10 to 12.5 μm, subhyaline, and contained 1 or 2 oil drops. The specific measurements and characteristics (especially falcate aerial hyphae) were consistent with those of Cystotheca wrightii Berk. & M.A. Curtis (1). Fungal DNA was extracted by the Chelex method. The internal transcribed spacer (ITS) region of rDNA of KUS-F27309 was amplified with primers ITS5/P3 and sequenced directly (4). The resulting 589-bp sequence was deposited in GenBank (Accession No. KF735066). A BLAST search in GenBank showed that the Korean isolate had 100% homology with C. wrightii on Q. glauca from Japan (AB000932). Powdery mildews of Q. glauca associated with C. wrightii have been known in Japan, Taiwan, and China (1,3), but not in Korea. Finding of C. wrightii on Q. glauca could pose a potential threat to other evergreen oak species in southern part of Korea.

Erysiphe viburni-plicati and Podosphaera photiniae, two new species of Erysiphales (Ascomycota) from Japan

Two new species of the Erysiphales, Erysiphe viburni-plicati and Podosphaera photiniae, are described and illustrated in this paper. These two fungi were first reported in 1977 and 1996 as Podosphaera spp. from Japan, but have not yet been formally described and named. We performed detailed morphological re-examinations and phylogenetic analyses based on new specimens. The results clearly show that these fungi are new, hitherto undescribed species. Molecular analyses of E. viburni-plicati indicate that this fungus belongs to the genus Erysiphe, not to Podosphaera, although it has chasmothecia with a single ascus. This result reveals that monoascus-type chasmothecia are not confined to Podosphaera and Cystotheca as they are also formed by some Erysiphe species.

First Report of Powdery Mildew Caused by Podosphaera xanthii on Papaya in Korea

In March 2013, papaya (Carica papaya L. cv. Sunrise) plants growing in polyethylene-film-covered greenhouses in Agricultural Research Center for Climate Change located in Jeju City, Korea, were observed severely affected by a powdery mildew. Symptoms appeared as circular to irregular white patches on both sides of the leaves. As the disease progressed, the plants were covered with dense masses of the spores, eventually causing senescence and withering of leaves. Voucher specimens were deposited in the Korea University Herbarium (KUS). Hyphae were flexuous to straight, branched, septate, and 5 to 8 μm wide. Conidiophores were 110 to 250 × 10 to 12.5 μm and produced 2 to 5 immature conidia in chains with a crenate outline followed by 2 to 3 cells. Foot-cells of conidiophores were straight, cylindric, slightly constricted at the basal septum, and 55 to 110 μm long. Conidia were hyaline, ellipsoid-ovoid, measured 22 to 38 × 18 to 21 μm with a length/width ratio of 1.2 to 1.8, and had distinct fibrosin bodies. Chasmothecia were scattered or partly clustered, dark brown, spherical, 80 to 100 μm in diameter, and each contained a single ascus. Appendages were mycelioid, 1- to 5-septate, brown at the base and becoming paler. Asci were sessile, 72 to 87 × 52 to 68 μm, had a terminal oculus of 17 to 23 μm wide, and contained 8 ascospores, each 17 to 23 × 12.5 to 15 μm. The morphological characteristics and measurements were consistent with those of Podosphaera xanthii (Castagne) U. Braun & Shishkoff (1). To confirm the identification, the complete internal transcribed spacer (ITS) region of rDNA of KUS-F27269 was amplified with the primers ITS5/P3 and sequenced (3). The resulting 443 bp sequence was deposited in GenBank (Accession No. KF111806). The Korean isolate showed >99% similarity with those of many P. xanthii isolates including an isolate on papaya from Taiwan (GU358450). Pathogenicity was confirmed through inoculation tests by gently pressing a diseased leaf onto young leaves of three asymptomatic, potted seedlings (cv. Sunrise). Three non-inoculated seedlings were used as control. Inoculated plants were isolated from non-inoculated plants in separate rooms in a greenhouse at 26 to 30°C. Inoculated leaves developed symptoms after 7 days, whereas the control plants remained symptomless. The fungus present on the inoculated leaves was identical morphologically to that observed on the original diseased leaves, fulfilling Koch's postulates. Powdery mildews of papaya caused by Podosphaera species including P. caricae-papayae have been reported in North America, South America, Hawaii, Africa, Ukraine, Australia, New Zealand, the Cook Islands, India, Thailand, Taiwan, and Japan (2,4). P. caricae-papayae is currently reduced to synonymy with P. xanthii (1). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on papaya in Korea. Though papaya is a minor crop in Korea, producing about 300 M/T annually in greenhouses, powdery mildew disease is a threat to safe production of the fruits.

Mal3, the Schizosaccharomyces pombe homolog of EB1, is required for karyogamy and for promoting oscillatory nuclear movement during meiosis

Two successive rounds of chromosome segregation following a single round of DNA replication enable the production of haploid gametes during meiosis. In the fission yeast Schizosaccharomyces pombe, karyogamy is the process where the nuclei from 2 haploid cells fuse to create a diploid nucleus, which then undergoes meiosis to produce 4 haploid spores. By screening a collection of S. pombe deletion strains, we found that the deletion of 2 genes, mal3 and mto1, leads to the production of asci containing up to 8 spores. Here, we show that Mal3, the fission yeast member of the EB1 family of conserved microtubule plus-end tracking proteins, is required for karyogamy, oscillatory nuclear movement, and proper segregation of chromosomes during meiosis. In the absence of Mal3, meiosis frequently initiates before the completion of karyogamy, thus producing up to 8 nuclei in a single ascus. Our results provide new evidence that fission yeast can initiate meiosis prior to completing karyogamy.

First Report of Powdery Mildew Caused by Podosphaera xanthii on the Invasive Weed, Bidens pilosa, in Korea

Bidens pilosa L., known as Spanish needle or cobbler's peg, is a cosmopolitan weed, originating from South America and common in all tropical and subtropical areas of the world. In Korea, this plant was first reported in 1992 (3), and has become naturalized widely by replacing indigenous plants and disrupting native ecosystems. In the autumn of 2012, hundreds of Spanish needles growing around an industrial complex in Milyang in southern Korea were observed to be severely infected with a powdery mildew. Symptoms first appeared as circular to irregular white patches, which subsequently showed abundant hyphal growth on both sides of the leaves, and on young stems and inflorescences. Red-purplish discoloration and crinkling of the leaves were also observed. Appressoria on the mycelium were nipple-shaped or nearly absent. Conidiophores measured 100 to 190 × 11 to 13 μm, and produced 2 to 5 immature conidia in chains with a crenate outline, at the end of 2 to 3 straight cells of the conidiophore. Conidia were hyaline, ellipsoid to barrel-shaped, measured 28 to 42 × 16.5 to 21 μm (length/width ratio of 1.4 to 2.0), and had distinct fibrosin bodies. Dark brown chasmothecia were found partly embedded in the mycelial felt on leaves and stems, were spherical, gregarious to scattered, and 80 to 100 μm in diameter. Each contained a single ascus and had a terminal oculus 17 to 23 μm wide. Asci were sessile, 70 to 90 × 52 to 65 μm, and contained eight ascospores, each 22 to 28 × 16 to 20 μm. The structures and measurements were consistent with those of Podosphaera xanthii (Castagne) U. Braun & Shishkoff (1). Specimens were deposited in the Korea University Herbarium (KUS). To confirm identity of the causal fungus, the complete internal transcribed spacer (ITS) region of rDNA of isolate KUS-F27201 was amplified with primers ITS5 and P3 (4), and sequenced directly. The resulting 476-bp sequence was deposited in GenBank (Accession No. KC484700). A GenBank BLAST search of this sequence revealed >99% similarity with those of many P. xanthii isolates on plants in the Asteraceae. Pathogenicity was confirmed through inoculation by gently pressing diseased leaf onto leaves of five healthy, potted, young Spanish needle plants. Five non-inoculated plants served as a control treatment. Plants were maintained in a greenhouse at 25 ± 2°C. Inoculated plants developed symptoms after 8 days, whereas the control plants remained symptomless. The fungus present on the inoculated plants was identical morphologically to that originally observed on diseased plants, fulfilling Koch's postulates. Powdery mildews of B. pilosa caused by Podosphaera species have been reported in North America, Africa, and Asia (India and China), but not from Korea (2). To our knowledge, this is the first report of powdery mildew caused by P. xanthii on Spanish needles in Korea. The field observations suggest that the powdery mildew could limit expansion of this invasive weed in Korea.

Outbreak of Cucurbit Powdery Mildew on Watermelon Fruit Caused by Podosphaera xanthii in Southwest Florida.

Cucurbit powdery mildew caused by the obligate parasite Podosphaera xanthii occurs commonly on foliage, petioles, and stems of most cucurbit crops grown in the United States. (3). However, in the field, fruit infection on cucurbits including watermelon (Citrullus lanatus), is rarely, if ever, observed (2). Consequently, it was atypical when severe powdery mildew-like symptoms were observed on seedless and seeded watermelon fruit on several commercial farms in southwestern Florida during November and December 2010. Severe powdery mildew was also observed on 'Tri-X 313' and 'Mickey Lee' fruit grown at SWFREC, Immokalee, FL. Infected fruit developed poorly and were not marketable. Powdery mildew symptoms were mainly observed on young immature fruit, but not on mature older fruit. Abundant powdery mildew conidia occurred on fruit surface, but not on the leaves. Conidia were produced in chains and averaged 35 × 21 μm. Observation of conidia in 3% KOH indicated the presence of fibrosin bodies commonly found in the cucurbit powdery mildew genus Podosphaera (3). Orange-to-dark brown chasmothecia (formerly cleisthothecia) containing a single ascus were detected on the surface of some fruit samples. Conidial DNA was subjected to PCR using specific primers designed to amplify the internal transcribed spacer (ITS) region of Podosphaera (4). The resulting amplicons were sequenced and found to be 100% identical to the ITS sequences of P. xanthii in the NCBI database (D84387, EU367960, AY450961, AB040322, AB040315). Sequences from the watermelon fruit isolate were also identical to several P. fusca (synonym P. xanthii), P. phaseoli (GQ927253), and P. balsaminae (AB462803) sequences. On the basis of morphological characteristics and ITS sequence analysis, the pathogen infecting watermelon fruit can be considered as P. xanthii (1,3,4). The powdery mildew isolate from watermelon fruit was maintained on cotyledons of squash (Cucurbita pepo, 'Early Prolific Straight Neck'). Cotyledons and leaves of five plants each of various cucurbits and beans were inoculated with 10 μl of a conidial suspension (105conidia/ml) in water (0.02% Tween 20). Two weeks after inoculation, abundant conidia were observed on cucumber (Cucumis sativus, 'SMR-58') and melon (Cucumis melo) powdery mildew race differentials 'Iran H' and 'Vedrantais'. However, no growth was observed on melon differentials 'PI 414723', 'Edisto 47', 'PMR 5', 'PMR 45', 'MR 1', and 'WMR 29' (2,3). The powdery mildew isolate from watermelon fruit behaved as melon race 1 (3). Mycelium and conidia were also observed on fruit surface of watermelon 'Sugar Baby' and a susceptible U.S. plant introduction (PI 538888) 3 weeks after inoculation. However, the disease was not as severe as what was observed in the fields in fall 2010. The pathogen did not grow on plants of Impatiens balsamina or on select bean (Phaseolus vulgaris) cultivars ('Red Kidney', 'Kentucky Blue', and 'Derby Bush'), but did grow and produce abundant conidia on 'Pinto bush bean'. Powdery mildew on watermelon fruit in production fields can be considered as a potentially new and serious threat requiring further studies to develop management strategies.

Meiosis Drives Extraordinary Genome Plasticity in the Haploid Fungal Plant Pathogen Mycosphaerella graminicola

Meiosis in the haploid plant-pathogenic fungus Mycosphaerella graminicola results in eight ascospores due to a mitotic division following the two meiotic divisions. The transient diploid phase allows for recombination among homologous chromosomes. However, some chromosomes of M. graminicola lack homologs and do not pair during meiosis. Because these chromosomes are not present universally in the genome of the organism they can be considered to be dispensable. To analyze the meiotic transmission of unequal chromosome numbers, two segregating populations were generated by crossing genetically unrelated parent isolates originating from Algeria and The Netherlands that had pathogenicity towards durum or bread wheat, respectively. Detailed genetic analyses of these progenies using high-density mapping (1793 DArT, 258 AFLP and 25 SSR markers) and graphical genotyping revealed that M. graminicola has up to eight dispensable chromosomes, the highest number reported in filamentous fungi. These chromosomes vary from 0.39 to 0.77 Mb in size, and represent up to 38% of the chromosomal complement. Chromosome numbers among progeny isolates varied widely, with some progeny missing up to three chromosomes, while other strains were disomic for one or more chromosomes. Between 15–20% of the progeny isolates lacked one or more chromosomes that were present in both parents. The two high-density maps showed no recombination of dispensable chromosomes and hence, their meiotic processing may require distributive disjunction, a phenomenon that is rarely observed in fungi. The maps also enabled the identification of individual twin isolates from a single ascus that shared the same missing or doubled chromosomes indicating that the chromosomal polymorphisms were mitotically stable and originated from nondisjunction during the second division and, less frequently, during the first division of fungal meiosis. High genome plasticity could be among the strategies enabling this versatile pathogen to quickly overcome adverse biotic and abiotic conditions in wheat fields.

Erysiphe monascogera sp. nov., an unusual powdery mildew fungus found on fruits of Styrax japonica

Morphological observations using light and scanning electron microscopes and molecular phylogenetic analysis revealed that the fungus growing on the surface of fruits or sepals of Styrax japonica collected at Nagano, Japan, is a new powdery mildew with an unusual morphology, described here as Erysiphe monascogera. This fungus has mainly a single ascus in a chasmothecium, but molecular phylogenetic analysis and the shape of the hyphal appressoria suggest that it is an Erysiphe species. Erysiphe monascogera is a sister-species to E. nomurae on Symplocos chinensis var. leucocarpa f. pilosa, although there are obvious morphological differences between the two species. This inconsistency between molecular phylogeny and morphology may be explained by the unique habitat of E. monascogera. Erysiphe monascogera and E. nomurae are included in a clade composed of the E. alphitoides complex, which suggests that these two species diverged by host jumping of the E. alphitoides complex, having oaks as major host plants.

<i>Erysiphe monascogera</i> sp. nov., an unusual powdery mildew fungus found on fruits of <i>Styrax japonica</i>

Morphological observations using light and scanning electron microscopes and molecular phylogenetic analysis revealed that the fungus growing on the surface of fruits or sepals of Styrax japonica collected at Nagano, Japan, is a new powdery mildew with an unusual morphology, described here as Erysiphe monascogera. This fungus has mainly a single ascus in a chasmothecium, but molecular phylogenetic analysis and the shape of the hyphal appressoria suggest that it is an Erysiphe species. Erysiphe monascogera is a sister-species to E. nomurae on Symplocos chinensis var. leucocarpa f. pilosa, although there are obvious morphological differences between the two species. This inconsistency between molecular phylogeny and morphology may be explained by the unique habitat of E. monascogera. Erysiphe monascogera and E. nomurae are included in a clade composed of the E. alphitoides complex, which suggests that these two species diverged by host jumping of the E. alphitoides complex, having oaks as major host plants.

Homothallism in Sclerotinia minor

Sclerotinia species are sexually reproducing ascomycetes. In the past S. minor and S. sclerotiorum, have been assumed to be homothallic because of the self-fertility of colonies derived from single ascospores. S. trifoliorum has previously been shown to be bipolar heterothallic due to the presence of four self-fertile and four self-sterile ascospores within a single ascus [Uhm, J.Y., Fujii, H., 1983a. Ascospore dimorphism in Sclerotinia trifoliorum and cultural characters of strains from different-sized spores. Phytopathology 73: 565–569]. However, isolates of S. minor and S. sclerotiorum were proven to be homothallic ascomycetes, by self-fertility of all eight ascospores within an ascus. Apothecia were raised from all eight ascospores of a single tetrad from four isolates of S. minor and from an isolate of S. sclerotiorum, indicating that inbreeding may be the predominant breeding mechanism of S. minor. Ascospores from asci of S. minor and S. sclerotiorum were predominantly monomorphic, but rare examples of ascospore dimorphism similar to S. trifoliorum were found.

Heterothallic mating observed between Mexican isolates of Glomerella lindemuthiana

Although several reports have described the occurrence of the teleomorphic state of Glomerella lindemuthiana (anamorph, Colletotrichum lindemuthianum), there has been a lack of continuity in this research. To identify G. lindemuthiana isolates capable of developing the teleomorphic state, 19 Mexican isolates were analyzed. Three types of response were observed: (i) negative, where only mycelial growth with or without acervuli was observed; (ii) potential, where in addition to the above, spherical perithecia-like structures were observed; (iii) positive, where perithecia containing asci and ascospores were observed. All strains were self-sterile and only one combination of strains produced fertile perithecia. From this fertile combination 168 individual ascospore cultures were isolated, including five from a single ascus. Forty-four monoascospore cultures were characterized with AFLP, confirming that these individuals were progeny from a sexual cross between the original two G. lindemuthiana isolates and that sexual reproduction in G. lindemuthiana is heterothallic in nature. Analysis of the parental strains with degenerate PCR primers indicated that sequences homologous to the HMG box of the MAT1-2 idiomorph are present in both parental isolates. This supports previous observations in other Glomerella species where the standard ascomycete configuration of distinct idiomorphs at the MAT locus does not hold true. The significance of these results is discussed.

Heterothallic mating observed between Mexican isolates of Glomerella lindemuthiana

Although several reports have described the occurrence of the teleomorphic state of Glomerella lindemuthiana (anamorph, Colletotrichum lindemuthianum), there has been a lack of continuity in this research. To identify G. lindemuthiana isolates capable of developing the teleomorphic state, 19 Mexican isolates were analyzed. Three types of response were observed: (i) negative, where only mycelial growth with or without acervuli was observed; (ii) potential, where in addition to the above, spherical perithecia-like structures were observed; (iii) positive, where perithecia containing asci and ascospores were observed. All strains were self-sterile and only one combination of strains produced fertile perithecia. From this fertile combination 168 individual ascospore cultures were isolated, including five from a single ascus. Forty-four monoascospore cultures were characterized with AFLP, confirming that these individuals were progeny from a sexual cross between the original two G. lindemuthiana isolates and that sexual reproduction in G. lindemuthiana is heterothallic in nature. Analysis of the parental strains with degenerate PCR primers indicated that sequences homologous to the HMG box of the MAT1-2 idiomorph are present in both parental isolates. This supports previous observations in other Glomerella species where the standard ascomycete configuration of distinct idiomorphs at the MAT locus does not hold true. The significance of these results is discussed.