Phragmidium satoanum,a new rust pathogen of Rosa hirtula in Japan

The causal fungus of a rust disease of Rosa hirtula, endemic to mountainous areas of Fuji-Hakone-Izu National Park, Japan, was thought to be a common species Phragmidium rosae-multiflorae. Continued field observations, morphological examination, and experimental inoculations proved that the fungus produced laterally three-angled aeciospores and urediniospores together with multi-cellular teliospores on the same R. hirtula trees. These morphological features were different from those of P. rosae-multiflorae. The fungus parasitized only R. hirtula. Experimental inoculations and field observations did not prove that R. banksiae, R. laevigata, and R. multiflora supported infection and sporulation of the fungus. Under the field observations, R. multiflora, the most common host of P. rosae-multiflorae, was not proven to harbor the R. hirtula fungus. Therefore, the fungus was concluded to be a species distinct from P. rosae-multiflorae; and a new name, P. satoanum, was proposed for it.     

Life cycle of Melampsora coleosporioides,a leaf rust of Salix babylonica in Japan

Melampsora coleosporioides produces uredinia and telia on the leaves of Salix babylonica. Since the life cycle of this fungus is largely unknown, inoculation experiments were conducted to find alternate host plants. Results showed that M. coleosporioides can use Corydalis incisa as a spermogonial and aecial host. The morphological characteristics of the spermogonial and aecial states of the fungus are first described. Furthermore, field observations and histological studies demonstrated that the fungus was able to overwinter in twigs of S. babylonica and produced urediniospores in early spring. Thus, the leaf rust occurs on S. babylonica every year and alternation with the spermogonial and aecial host is not necessary.     

Phylogenetic study of indigenous grapevine leaf rust fungi in North America and biological identity of an invasive grapevine leaf rust fungus in Brazil

Two American grapevine leaf rust (GLR) fungi, Phakopsora muscadiniae and P. uva, were found to be phylogenetically different from Asian-Australasian GLR fungi. In the phylogram based on rDNA region sequences, a clade of the American fungi was sister to an inclusive clade of three autoecious species on Meliosma and a heteroecious species host-alternating between Meliosma and Parthenocissus. An invasive Brazilian GLR fungus (as P. meliosmae-myrianthae) was included in the Asian-Australasian GLR fungi clade, or the clade of the Thai population of Phakopsora sp. It could be assumed that the Brazilian GLR fungus originated from an inadvertently introduced Thai population.     

Mycoparasitism of Phakopsora pachyrhizi,the soybean rust pathogen,by Simplicillium lanosoniveum

Rust of soybean, caused by Phakopsora pachyrhizi, was first reported in the southeastern US in 2004 where it quickly became established. Yield losses ranged from 35% to more than 80%. The mycophilic fungus Simplicillium lanosoniveum was previously shown to colonize rust pustules on soybean leaves and prevent germination of urediniospores. The number of pustules on soybean leaves also was significantly reduced when S. lanosoniveum colonized leaves. This study examined the antagonistic interactions between P. pachyrhizi and S. lanosoniveum using confocal, transmission (TEM) and scanning electron microscopy (SEM) in order to determine if S. lanosoniveum was mycoparasitic. Co-inoculated detached soybean leaves were examined using TEM and SEM to examine changes in urediniospores colonized by S. lanosoniveum. An isolate of S. lanosoniveum, previously shown to be an antagonist of P. pachyrhizi, was transformed with the green fluorescent protein (GFP) gene and used to document the infection process using confocal microscopy. S. lanosoniveum colonized pustules and coiled around urediniospores before infection. The mycoparasite penetrated urediniospores through germ pores within 24 h after inoculation, at which time organelles showed signs of degradation. By 2 days after inoculation, there was extensive colonization of urediniospores by hyphae of S. lanosoniveum. Hyphae of the mycoparasite erupted from the colonized urediniospores at 7 days after inoculation, and there was extensive sporulation on the surface of urediniospores. Over 90% of urediniospores were colonized within 5 days after inoculation with the mycoparasite. We showed in previous studies that S. lanosoniveum is an antagonist of P. pachyrhizi as well as an effective biocontrol agent, but we were unable to document its mode of action. We now present microscopic evidence that S. lanosoniveum is a mycoparasite.     

Ochropsora staphyleae,a new rust pathogen of Japanese bladdernut,found in central Japan

Japanese bladdernut shrub, Staphylea bumalda (Staphyleaceae), was found infected by a fungus in Prefectures of Ibaraki and Tochigi, central Japan. The fungus produced telia beneath the host epidermis and basidiospores on metabasidia emerging from the sori on the abaxial leaf surface. Probasidia were single-celled, sessile, short-cylindrical, thin-walled, and laterally free. A four-celled metabasidium arose from a probasidium by apical elongation. Apparent biotrophic nature and the basidium morphology of the Staphylea fungus suggested its taxonomic affinity to the rust genus Ochropsora. Molecular phylogenetic analyses of D1/D2 region of LSU rDNA showed that two collections of the fungus were grouped with Ochropsora ariae (type species of the genus) and O. nambuana but formed an independent clade. The fungus under consideration was, therefore, classified in Ochropsora, and a new name, O. staphyleae, was proposed for it.     

Foliar pathogens of Populus angustifolia are consistent with a hypothesis of Beringian migration into North America

Populus angustifolia, the narrowleaf cottonwood, is considered one of two native species of Populus section Tacamahaca restricted to western North America. Efforts to construct a definitive phylogeny of Populus spp. are complicated by ancient hybridization, but some phylogenetic analyses suggest P. angustifolia is more closely related to Asian congeners than to Populus trichocarpa, the other species of Populus section Tacamahaca in western North America. Because hosts and their obligate symbionts can display parallel phylogeographic patterns, we evaluated the possibility of a Beringian migration into North America by an Asian ancestor of P. angustifolia by determining the distributions, host preferences, and, in some cases, closest phylogenetic relatives of fungal leaf pathogens of P. angustifolia. Phyllactinia populi, a common foliar pathogen on Populus spp. in Asia but unknown on P. trichocarpa, was found on P. angustifolia in multiple sites. Mycosphaerella angustifoliorum, also unknown on P. trichocarpa, was commonly collected on P. angustifolia. Conversely, many common foliar pathogens of P. trichocarpa in western North America were not found on P. angustifolia; only Melampsora×columbiana and Drepanopeziza populi were common to both Populus species. Phylogenetic analyses revealed that M. angustifoliorum was not part of the diversification of Mycosphaerella on Populus that includes all other Mycosphaerella species on Populus in North America: Mycosphaerella populicola, Mycosphaerella populorum, M. sp. 1, and M. sp. 2. The latter two undescribed species represent a newly discovered diversification of M. populorum in western North America. Overall, the leaf pathogen community of P. angustifolia is consistent with a Beringian migration into North America by the ancestor of P. angustifolia.     

Unveiling Gymnosporangium corniforme, G. unicorne, and G. niitakayamense sp. nov. in Taiwan

Three rust fungi from high mountains and pear-producing areas in Taiwan were described using morphological and molecular data based on 34 specimens. Gymnosporangium corniforme was demonstrated to produce spermogonia and aecia on Sorbus randaiensis based on molecular analyses and inoculation experiments. The pear rust pathogen G. unicorne was discovered in Taiwan for the first time. Gymnosporangium niitakayamense sp. nov. was observed on the leaves of Photinia niitakayamensis. It was distinct from other species in peridial cell wall structures, i.e., smooth outer wall, rugose side wall, and coralloid projections on the inner wall, and in having echinulate aeciospores.