Hye Young Yun

Antagonistic Bacillus species as a biological control of ginseng root rot caused by Fusarium cf. incarnatum

Background This study aimed to develop a biocontrol system for ginseng root rot caused by Fusarium cf. incarnatum. Methods In total, 392 bacteria isolated from ginseng roots and various soils were screened for their antifungal activity against the fungal pathogen, and a bacterial isolate (B2-5) was selected as a promising candidate for the biocontrol because of the strong antagonistic activity of the bacterial cell suspension and culture filtrate against pathogen. Results The bacterial isolate B2-5 displayed an enhanced inhibitory activity against the pathogen mycelial growth with a temperature increase to 25°C, produced no pectinase (related to root rotting) and no critical rot symptoms at low [106 colony-forming units (CFU)/mL] and high (108 CFU/mL) inoculum concentrations. In pot experiments, pretreatment with the bacterial isolate in the presumed optimal time for disease control reduced disease severity significantly with a higher control efficacy at an inoculum concentration of 106 CFU/mL than at 108 CFU/mL. The establishment and colonization ability of the bacterial isolates on the ginseng rhizosphere appeared to be higher when both the bacterial isolate and the pathogen were coinoculated than when the bacterial isolate was inoculated alone, suggesting its target-oriented biocontrol activity against the pathogen. Scanning electron microscopy showed that the pathogen hyphae were twisted and shriveled by the bacterial treatment, which may be a symptom of direct damage by antifungal substances. Conclusion All of these results suggest that the bacterial isolate has good potential as a microbial agent for the biocontrol of the ginseng root rot caused by F. cf. incarnatum.

First Description of Coleosporium plectranthi Causing Perilla Rust in Korea

Perilla rust is a damaging disease in perilla cultivation in Korea. Its causal agent was identified as Coleosporium plectranthi based on descriptions of morphological characteristics of spores and spore-producing fruiting structures (in uredinial and telial stages from perilla and in aecial stage from the alternate host pine) collected in 15 locations in Korea during the disease survey from 2004 to 2006. These characteristics were yellow or orange uredinium; globose or ellipsoid urediniospore of 20.8 μm×18 μm in size; verruca of 0.3 mm×1.2 mm; orange telium; one-celled, oblong ellipsoid teliospore of 63.1 μm×19.7 μm with one-layered crusts or four-celled (when mature), internal basidium of 64.2 μm×19.7 μm; ellipsoid to globoid basidiospore of 20.3 μm×12 μm; type 2 spermogonium; yellow, broadly ellipsoid peridial cell of 35.6 μm×23.1 μm; and broadly ellipsoidal or subglobose aeciospore of 25.9 μm×18.8 μm. Phylogenetic analysis of 28S rDNA sequences revealed the closest relatedness to those of the genus Coleosporium, a monophyletic group distinguished from other rust fungi and divided into two main lineages, one of which was C. plectranthi grouped with high bootstrap value (96%). In pathogenicity test, both aeciospores and urediniospores caused rust development on perilla leaves. This is the first description of C. plectranthi causing perilla rust with the first findings of its telial stage on perilla and the first rust disease on the aecial host in Pinus densiflora. These aspects would provide basic information for the development of control measures of the disease.

The rust fungus Gymnosporangium in Korea including two new species, G. monticola and G. unicorne.

A survey was conducted of the rust fungus Gymnosporangium in Korea. We recollected previously known species, namely Gymnosporangium asiaticum, G. clavariiforme, G. globosum, G. japonicum and G. yamadae. Gymnosporangium nidus-avis and G. sabinae are reported for the first time from Korea, and two new species, G. monticola sp. nov. and G. unicorne sp. nov., are recognized. Previous single reports of G. miyabei and G. shiraianum could not be confirmed. The LSU rDNA was sequenced from freshly collected specimens. Phylogenetic analyses show that species of Gymnosporangium form a monophyletic group with strong bootstrap support within the rust fungi. The two new species are unique based on both A and B molecular as well as morphological characteristics. Analyses of phenotypic characters mapped onto the phylogenetic tree show that teliospore length followed by telia shape and telia length are conserved; these are morphological characters useful in differentiating species of Gymnosporangium. Each of the nine species of Gymnosporangium in Korea is described and illustrated, and keys based on aecia and telia stages are provided. Lectotype specimens for several names described in Gymnosporangium are designated.

The rust genus Frommeella revisited: a later synonym of Phragmidium after all

Frommeëlla (Phragmidiaceae, Pucciniales, Basidiomycota), which currently includes two species and is typified by F. tormentillae, causes rust on members of tribe Potentilleae (Rosaceae). The genus has been distinguished from Phragmidium on the basis of having only one germ pore per teliospore cell rather than two or three and by aecial characters. Phylogenetic analyses of both currently accepted Frommeëlla spp. with nLSU rDNA data suggest that Frommeëlla was derived from within a clade representing Phragmidium. Thus Frommeëlla should be considered to be a later generic synonym of Phragmidium. Analyses also indicate that Frommeëlla tormentillae on Potentilla species includes two taxa recognized herein as Phragmidium potentillae-canadensis and P. tormentillae. Frommeëlla mexicana on Potentilla spp. formerly classified in Duchesnea, is distinct from but sister to the other two species. Based on data regarding type specimens that were presented in a study by McCain and Hennen, the new combination Phragmidium mexicanum is proposed as the correct name for this species. Necessary studies of original material were made, and Phragmidium potentillae-canadensis is lectotpyified and epitypified. Although considered and expanded here, further examination of species boundaries and host ranges of the fungi formerly classified in Frommeëlla is warranted.

First Report of Japanese Apple Rust Caused by Gymnosporangium yamadae on Malus spp. in North America

Plants in the genus Malus Mill. are grown in temperate regions for fruit crops such as apple and ornamental landscape plants such as flowering crab apple. Gymnosporangium yamadae Miyabe ex G. Yamada, cause of Japanese apple rust, is known to attack economically important species of Malus in Asia. In August 2004 and July 2008, the aecial stage of a rust fungus was observed in Wilmington, DE and nearby in Media, PA on leaves of toringo crab apple (Malus toringo (Siebold) Siebold ex de Vriese), a cultivated plant native to Asia. On the basis of morphological and molecular characteristics, the fungus was identified as G. yamadae. This pathogen has not been previously reported in North America. The identification was confirmed by morphological comparisons with specimens of G. yamadae from Asia and descriptions (1-3) as well as using the D1/D2 domain of 28S rDNA sequence data G. clavariiforme (GenBank Accession No. AR426211), G. clavipes (GenBank Accession No. DQ354545), G. cornutum (GenBank Accession No. AF426210), G. juniperi-virginianae (GenBank Accession Nos. AF522167, AY629316, and DQ354547), G. libocedri (GenBank Accession No. AF522168), G. sabinae (GenBank Accession Nos. AF426209 and AY512845) and G. yamadae (GenBank Accession Nos. FJ559373 and FJ559375). The specimens from North America included aecia of G. yamadae that are foliicolous, hypophyllous, roestelioid, and 4 to 7 mm high. The peridia are yellow-brown to brown and cornute to tubular with a closed brown tip at the apex and lacerate sides; the peridial remains often form a reticulate pattern. The peridial cells are long-narrow rhomboid, 83 to 120 μm long with smooth outer walls and verrucose to echinulate inner and side walls. The aeciospores are globose, 18 to 28 × 19 to 29 μm, with a slightly coronate surface and brown-yellow walls 2 to 3 μm thick. The telia known on Juniperus spp. were not observed. The specimens were deposited in the U.S. National Fungus Collections (BPI 878846, BPI 878847, BPI 878848, and BPI 878849). The 28S rDNA sequence of G. yamadae from BPI 878849 was deposited in GenBank as Accession No. FJ455091. Aecia of G. juniperi-virginianae, cause of cedar apple rust, differ from G. yamadae in having recurved peridial walls at maturity. References: (1) F. D. Kern. A Revised Taxonomic Account of Gymnosporangium. Pennsylvania State University Press, University Park, PA, 1973. (2) S. K. Lee and M. Kakishima. Mycoscience 40:109, 1999. (3) S. K. Lee and M. Kakishima. Mycoscience 40:121. 1999.

Tubakia subglobosa Causes Leaf Spots on Ring-Cupped Oak Trees in Korea

Ring-cupped oak, Quercus glauca Thunb., is an evergreen broadleaf tree growing up to 15 to 20 m tall. It is native to eastern Asia (China, Japan, Taiwan, and Korea). In Korea, it is distributed in the islands of the southern part of the peninsula, mostly in Jeju Island, South Korea. This species is planted as a windbreak and as an ornamental tree in urban forest areas and its fruit, leaves, and bark have been used in medicine. Small, dark-brownish leaf spots with a tiny yellowish center were observed on ring-cupped oak leaves in Jeju Island from May to July 2015, most extensively at an altitude of 203 to 228 m above sea level (33°28.087′N, 126°29.589′E). Symptoms enlarged with time, becoming distinctive epiphyllous lesions with a necrotic margin. Tiny, brownish, disc-shaped, crustose conidiomata composed of scutella, columella, and conidia (typical of the genus Tubakia), resembling grains of dust, were produced around and over the lesions. From these, a fungus was consistently isolated and cultured on malt extract agar (MEA). Specimens from Jeju Island and their cultures were deposited at the Herbarium of the Korean Forest Research Institute, Seoul, South Korea (HKFRI) and the Korean Collection for Type Cultures, Jeonbuk, South Korea (KCTC), with accession numbers HKRFI4093 and HY4604 (KCTC46432), and HKRFI4094 and HY4702 (KCTC46433). On MEA, fungal cultures formed creamy, cinnamon-colored colonies in the center, with concentric rings of aerial mycelium with a scalloped margin. Scutella on leaves were septate, leaves have radiating, septate hyphae, irregular at margin, usually tufted, brown to dark-brown, 80 to 150 μm in diameter; columellae were parenchymatous, 12 to 18 × 6 to 9 μm in size; conidia were subglobose, hyaline to reddish brown, 10 to 13 × 9 to 11 μm in size. Microconidia were not observed. These macro- and micromorphological traits closely fitted to those of Tubakia subglobosa (Diaporthales), which was described from Japan (Yokoyama and Tubaki 1971). ITS rDNA was PCR-amplied using primers (ITS1F/ITS4) and sequences (612 bp each) of the two fungi were analyzed and compared using BLAST search with sequence data from a Japanese T. subglobosa culture (CBS193.71, KY952636) from CBS-KNAW culture collection, and with sequences from our two isolates of T. subglobosa deposited in GenBank (accession nos. KY934453 and KY934454). Our fungus showed complete sequence homology to these T. subglobosa isolates, confirming its identity as T. subglobosa. In order to carry out the pathogenicity test, fungal spores produced on sterilized ring-cupped oak leaves were wound-inoculated on the main veins of the tree leaves as in Harrington et al. (2012). Small dark-brownish spots, with a yellowish center, matching initial natural symptoms, were produced 13 days after inoculation. Brownish disc-shaped conidiomata were formed on or around the necrotic spots, from which the fungus was reisolated, thus fulfilling Koch’s postulates. To our knowledge, this is the first report on the occurrence of T. subglobosa on Q. glauca in Korea.