Echinulate Urediniospores Research Articles

Two new Phragmidium species identified on Rosa plants native to China

Two new Phragmidium species, Phragmidium zhouquensis and Ph. longissima, were identified on two native plants, Rosa omeiensis and R. lichiangensis respectively, during an investigation of the occurrence of rust fungi in western China. Phragmidium zhouquensis is mainly characterized by 3–9-celled teliospores bearing minute verrucae on the surface. Phragmidium longissima differs from other Phragmidium species in that it possesses echinulate urediniospores with a pore membrane at the germ pore. Phylogenetic analyses based on 28S rRNA partial gene sequences revealed that specimens of Ph. zhouquensis and Ph. longissima formed two distinct lineages. Phragmidium longissima is the first Phragmidium species to be identified on R. lichiangensis.

Natural infectious behavior of the urediniospores of Melampsora larici-populina on poplar leaves

The uredinial stage in the life cycle of Melampsora larici-populina on poplar leaves is the most important pathogenic phase. We captured partial phases of uredinial infection in the wild, aiming to reconstruct the process of uredinial ontogeny by using scanning and transmission electron microscope. At the initial infection stage, germ tubes germinated from the echinulate urediniospores. Germ tubes were frequently seen to merge with the leaf surface and cuticle breakage was observed, indicating direct hyphal penetration. Stomata penetration occurred commonly, sometimes with more than one germ tube penetrating the same stoma. Melampsora larici-populina did not form appressoria in the infection process, implying that infectious behavior of this pathogen may differ from the other rust pathogens. In general, germ tubes branched randomly, and no distinct evidence indicated that stoma could induce or orient germ tube branches. However, oriented germ tube growth has been occasionally observed in other studies. The urediniospores collapsed and finally wizened when they became nutrient stressed. At the last stage of infection, the uredinia erupted from the leaf epidermis and appeared as orange pustules on the leaf surface.

First Report of Orange Rust of Sugarcane Caused by Puccinia kuehnii in Ecuador.

Orange rust, Puccinia kuehnii (W. Krüger) E.J. Butler, is an important disease of sugarcane (complex hybrid of Saccharum L. species) that causes up to 53% yield loss (3), and can eliminate sugarcane clones in breeding programs. Initially confined to the Asia-Oceania region, P. kuehnii was reported in Florida in June 2007 (2) followed by confirmation in Central and South America. Orange rust pustules were observed on August 5, 2011, in commercial sugarcane fields located in the Ecuadorian Pacific coast of South America. Pustules were observed on cultivar SP79-2233 and sugarcane clones of the CINCAE breeding program (EC06-351, EC06-340, and EC01-744). Low levels of disease incidence and severity were observed in the sugarcane germplasm. Observation under a light microscope showed typical irregularly echinulate urediniospores that were pale in color with thickened apices and paraphyses inconspicuous to absent, such as those reported to be P. kuehnii (4). DNA of urediniospores were extracted and amplified using Pk1F and PK1R qPCR primers (5). Additionally, the 28s large ribosomal subunit DNA was sequenced (1), resulting in a qPCR and 100% sequence identity with a partial sequence of the P. kuehnii 28S ribosomal RNA gene, accession GU058010 (932/932 base pairs, GenBank Accession No. KF202306). Based on urediniospore morphology, DNA amplification, and sequence analysis, the causal agent of the rust observed in Ecuador was confirmed to be P. kuehnii. Commercial varieties have not yet shown symptoms of infections. However, a survey conducted in 2011 and 2012 showed an increase of disease severity from 3% to 28% in the susceptible cv. SP79-2233. Disease symptoms were evident from stalk growth to maturity (7 to 12 months), especially at the beginning of the harvesting season. To our knowledge, this is the first report of the presence, distribution, and disease spread by the sugarcane orange rust pathogen P. kuehnii in Ecuador.

First Report of Cane and Leaf Rust on Rubus fruticosus Caused by Kuehneola uredinis in Korea

In September 2011, we observed a rust disease affecting about 90% of the leaves of several Rubus fruticosus L. plants at Andong (36°32'12.4″ N, 128°47'20.1″ E), Korea. Pustule formation occurred on cane surfaces and on the undersurfaces of leaves, with yellowing, reddening, and necrosis on the corresponding upper leaf surface. Leaf distortion and senescence also occurred. For light and scanning electron microscopy, uredinia were detached from leaf lesions using a razor blade and then mounted in water without staining. Leaves with lesions were prepared by gold sputtering and then observed by SEM (Hitachi S-2500C microscope, Japan). We observed the development of uredinial colonies with abundant sporulation. The echinulate urediniospores, which were 16.3 to 19.8 × 17.5 to 25.3 μm, were yellowish or occasionally pale brown, with a globose or subglobose shape (2). Telia were a floccose and pale yellowish-buff or almost white. Teliospores were four- to seven-celled. Cells were trapezoid-cylindric, 15 to 40 × 14 to 24 μm, with hyaline walls. Cell wall surface was smooth but often bearing coronate projections or bumps at the top (in apical cells) or upper rim (in intercalary cells). Cell wall thickness was about 0.5 μm at the sides and 2 to 4 μm at the apex; apical pores occurred on short cell-wall projections. Teliospore pedicels were short (0.17 to 1.34 × 0.78 to 1.45 μm), hyaline, and fragile (3). The pathogen was identified as Kuehneola uredinis L. on the basis of morphology (3), and this identification was confirmed by internal transcribed spacer (ITS) analysis. ITS rDNA of the fungus was amplified using the ITS1 and ITS4 primer set (ITS1: 5'-TCCGTAGGTGAACCTGCGG-3', ITS4: 5'-TCCTCCGCTTATTGATATGC-3'). BLAST analysis of the PCR product showed that the sequence shared 99% identity with the published nucleotide sequences for K. uredinis (Accession No. EU14069). The D1/D2 domain of 28S rDNA was amplified by PCR using the primer pair 5'-ACCCGCTGAAYTTAAGCATAT-3' and 5'-CTTCCTTGGTCCGTGTTTCAAGACGG-3' (1). Phylogenetic analysis using 28S rDNA sequences identified the causal fungus as K. uredinis. The identity of the fungus was confirmed as K. uredinis by DNA sequencing; the sequence was 99% similar to that of other K. uredinis (AF426218, AY745696, DQ354551, and GU058013). To the best of our knowledge, this is the first report of an outbreak of cane and leaf rust on Rubus fruticosus Linné caused by K. uredinis in Korea.

First Report of Soybean Rust Caused by Phakopsora pachyrhizi on Erythrina herbacea (Coral Bean).

Soybean rust (SBR), caused by the obligate fungus Phakopsora pachyrhizi Syd. & P. Syd., was initially reported on soybean (Glycine max L.) in Louisiana in 2004 and has since been reported on soybean and/or kudzu (Pueraria lobata (Willd.) Ohwi) in 9 states in 2005, 15 states in 2006, and 19 states in 2007 (1). The host range of P. pachyrhizi includes plants that are all in the Fabaceae or legume family. Six plant species in the United States have been reported as hosts of P. pachyrhizi: soybean, kudzu, Florida beggarweed (Desmodium tortuosum (Sw) DC.), dry bean (Phaseolus vulgaris L.), lima bean (P. lunatus L.), and scarlet runner bean (P. coccineus L.) (4). On 17 April 2008, a rust disease was observed on a weedy legume host with red showy flowers that was growing with kudzu in an overgrown vacant lot in the understory of live oak trees (Quercus virginiana Mill.) in Citra, FL. The discovery was made during routine scouting of this Integrated Pest Management Pest Information Platform for Extension and Education (IPM PIPE) mobile sentinel plot (3). The plant was confirmed by University of Florida botanists to be Erythrina herbaceae L., commonly known as coral bean. Coral bean is native to the southeastern United States and also is planted as a perennial ornamental. A sample of leaves exhibiting rust pustules characteristic of P. pachyrhizi uredinia was collected and examined with a microscope. Brown-to-brick red, angular lesions that were 3 to 11 mm in diameter (average 6.75 mm) were observed on the undersides of the leaves of two trifoliates. Within these lesions, there were several uredinia, some exuding hyaline, echinulate urediniospores (20 × 25 μm). The visual diagnosis and the species of the rust fungus were confirmed to be P. pachyrizi by a real-time PCR protocol (2). The diagnosis on this new host was verified by a USDA, APHIS National Mycologist in Beltsville, MD. Coral bean may serve as an additional overwintering host for P. pachyrhizi in the southeast. To our knowledge, this is the first report of soybean rust caused by P. pachyrhizi on E. herbaceae.

Late Season Occurrence of Soybean Rust Caused by Phakopsora pachyrhizi on Soybean in Illinois.

Soybean rust, first reported in the continental United States in Louisiana in 2004 (2), is one of the most important foliar diseases of soybean worldwide. On 10 October 2006, 20 soybean leaflets from 20 plants at physiological maturity were arbitrarily collected in research plots near Glendale, IL at the University of Illinois Dixon Springs Agricultural Center in Pope County and sent by overnight courier. On 11 October, leaflets were examined with a dissecting microscope at the Soybean Disease Laboratory at the National Soybean Research Center, and then at the Plant Disease Clinic, University of Illinois. Tan, angular lesions that were 2 to 4 mm in diameter were observed on the lower leaf surfaces of two of the 20 leaflets. Within these lesions, there was one uredinum on one leaflet and four on the other leaflet exuding hyaline, echinulate urediniospores (20 × 25 μm). On 11 October 2006, these leaflets were sent by overnight courier to the USDA/APHIS/PPQ/NIS Laboratory, Beltsville, MD Plant Disease Clinic for identification by morphological examination and by PCR using primers specific to Phakopsora pachyrhizi (1). Both tests confirmed the presence of P. pachyrhizi. The 18 leaflets that did not have sporulating pustules on 11 October were incubated in the laboratory for 5 days at near 100% relative humidity. Following incubation, nine leaflets were observed to have uredinia exuding urediniospores with a range of 1 to 43 uredinia per leaflet. These results indicate that incubation may be necessary to maximize the potential to observe uredinia exuding urediniospores. To our knowledge, this is the first report of P. pachyrhizi infecting plants in Illinois.

First Report of Phakopsora pachyrhizi, the Causal Agent of Asian Soybean Rust, on Florida Beggarweed in the United States.

Phakopsora pachyrhizi Syd. & P. Syd., which causes Asian soybean rust (SBR), was observed on Florida beggarweed, Desmodium tortuosum (Sw) DC., in Attapulgus, GA during late October and early November 2005. Tan to brown lesions (<1.0 mm in diameter) consistent with symptoms of SBR (2) were observed on older leaves of several plants collected near an SBR-infected soybean trial. Dissection (40 to 60×) and compound microscopy (×200 to 400) revealed conical pustules and ellipsoid, echinulate urediniospores (average size 15 × 20 μm) on the abaxial leaf surface. Polymerase chain reaction (PCR) (primers Ppm1 and Ppa2) (1) was conducted on four samples to confirm identification of P. pachyrhizi or P. meibomiae. Three were positive for P. pachyrhizi, and one was negative for both species. Using morphology and real-time PCR, SBR was confirmed as P. pachyrhizi by the USDA/APHIS in Beltsville, MD. Six noninfected Florida beggarweed plants were transplanted to pots during December 2005 and grown at 22 to 24°C in a greenhouse. On 11 January 2006, a water suspension of urediniospores collected from SBR-infected soybeans (1 × 105 spores per ml) was spray inoculated on all leaves to almost runoff and incubated for 48 h in a plastic humidity chamber. Lesions, pustules, and urediniospores consistent with SBR (2) were observed on 3 February 2006. A PCR assay was conducted on six samples from the infected greenhouse plants and all were positive for P. pachyrhizi. Florida beggarweed is widespread in the southern United States and may serve as an additional overwintering source for P. pachyrhizi and a potential inoculum source for the soybean crop.

Desmosorus, a new rust genus (Uredinales)

Uredo behnickiana (syn. Hemileia americana and H. oncidii) is known on orchids of the genera Cattleya, Epidendrum, Laelia, Lophiaris and Oncidium. Previously, only the uredinial stages of these fungi have been described. The telial stage of the rust species was found for the first time on Oncidium marshallianum. Because of a unique combination of morphological characters the fungus could not be assigned to Hemileia or any other known rust genus. Desmosorus is proposed, therefore, as a new genus with Desmosorus oncidii as the single known species. Desmosorus is characterised by (1) suprastomatal sori on which the spores are formed at the ends of branched hyphae, by (2) subglobose to ovoid, echinulate urediniospores with a smooth patch around the hilum and by (3) thin-walled, oblong elliptical to cylindrical teliospores with a rounded apex.

Attraction of Twospotted Spider Mite to Bean Rust Uredinia

Adults of the twospotted spider mite, Tetranychus urticae, were two- to sixfold greater on bean leaves, Phaseolus vulgaris, containing multiple uredinia of the rust fungus, Uromyces appendiculatus, than on rust-free bean leaves. On rust-free plants, freshly released mites went to the young trifoliolate leaves; but on rust-infected plants, they initially migrated to uredinia on older leaves. Mites became covered with echinulate urediniospores and vectored them to rust-free plants. The smooth-walled teliospores seldom adhered to the mites

A Bright-Field and Scanning Electron Microscopic Study of the Development ofPuccinia ZoysiaeonZoysiaSpecies andPaederia Scandens

The development of the heteroecious, macrocyclic rust Puccinia zoysiae on zoysiagrasses (Zoysia spp.) and Paederia scandens was studied using bright-field and scanning electron microscopy. This fungus grows intercellularly through the mesophyll of the zoysiagrass leaf, invading parenchyma cells, and forming haustoria. However, its growth is restricted by the vascular bundles and the bulliform cells, which the fungus does not penetrate. As a consequence, longitudinal lesions are formed, predominantly on the adaxial leaf surface. Soon after the onset of infection, paraphyses and echinulate urediniospores are produced, and are rapidly exposed due to rupture of the epidermis. Teliospores form later, first within the uredinia, and subsequently in telia which appear on both leaf surfaces. These spores are two-celled, persistent, and pedicellate. They germinated after two months of suspension in water at 4 C, followed by exposure to a saturated atmosphere for 24 hours. Germination begins with the emergence of a basidium (promycelium) from either or both cells of the teliospore. This is followed by the formation of septa and sterigmata from which basidiospores arise. These spores infect leaves of P. scandens, producing inconspicuous, intercellular spermogonia. Aecia form intercellularly and eventually erupt through the lower leaf surface. The aecial peridium has an unusual double-layered wall, the inner wall of which consists of non-viable aeciospores. Aeciospores are verrucose and are produced in basipetal succession.

A Bright-Field and Scanning Electron Microscopic Study of the Development of Puccinia zoysiae on Zoysia Species and Paederia scandens

The development of the heteroecious, macrocyclic rust Puccinia zoysiae on zoysiagrasses (Zoysia spp.) and Paederia scandens was studied using bright-field and scanning electron microscopy. This fungus grows intercellularly through the mesophyll of the zoysiagrass leaf, invading parenchyma cells, and forming haustoria. However, its growth is restricted by the vascular bundles and the bulliform cells, which the fungus does not penetrate. As a consequence, longitudinal lesions are formed, predominantly on the adaxial leaf surface. Soon after the onset of infection, paraphyses and echinulate urediniospores are produced, and are rapidly exposed due to rupture of the epidermis. Teliospores form later, first within the uredinia, and subsequently in telia which appear on both leaf surfaces. These spores are two-celled, persistent, and pedicellate. They germinated after two months of suspension in water at 4 C, followed by exposure to a saturated atmosphere for 24 hours. Germination begins with the emergence of a basidium (promycelium) from either or both cells of the teliospore. This is followed by the formation of septa and sterigmata from which basidiospores arise. These spores infect leaves of P. scandens, producing inconspicuous, intercellular spermogonia. Aecia form intercellularly and eventually erupt through the lower leaf surface. The aecial peridium has an unusual double-layered wall, the inner wall of which consists of non-viable aeciospores. Aeciospores are verrucose and are produced in basipetal succession.

Blastospora Itoana on Smilax Nipponica forms a Caeoma Stage on Prunus Grayana in Japan

A caeomatoid rust fungus on Prunus grayana is proved to be an aecial anamorph of Blastospora itoana, whose uredinial and telial stages occur on Smilax nipponica and S. riparia. The Caeoma stage is determined as C. radiatum. Aciculate aeciospores and completely echinulate urediniospores separate B. itoana from B. smilacis with verrucose aeciospores and incompletely echinulate urediniospores.

Blastospora itoana on Smilax nipponica Forms a Caeoma Stage on Prunus grayana in Japan

A caeomatoid rust fungus on Prunus grayana is proved to be an aecial anamorph of Blastospora itoana, whose uredinial and telial stages occur on Smilax nipponica and S. riparia. The Caeoma stage is determined as C. radiatum. Aciculate aeciospores and completely echinulate urediniospores separate B. itoana from B. smilacis with verrucose aeciospores and incompletely echinulate urediniospores.

Autoecious species of Puccinia on Cichorieae in North America

Seventeen autoecious species of Puccinia occurring on Cichorieae (Asteraceae) in North America were studied. The taxa removed from those usually treated synonymously with P. hieracii include: P. troximontis Pk. and P. hypochaeridis Oud., which are segregated because of their completely echinulate urediniospores. Puccinia agoseridis sp.nov. is also segregated from the same complex because of difference in teliospore wall sculpturing. Both varieties of P. harknessii stand apart from P. hieracii by their more conspicuous teliospore warting. Puccinia harknessii var. harknessii attacks Lygodesmia while P. harknessii var. stephanomeriae comb.nov. occurs on Stephanomeria. Puccinia chondrillina is separated from P. hieracii by its smaller urediniospore tonsures and P. lapsanae possesses tonsures which are absent in P. variabilis. Such morphological differences become more evident with the use of scanning electron microscope examination to support observations with the light microscope.

Surface structure of the urediniospores of Puccinia coronata f. sp. avenae

The surface structure of the echinulate urediniospores of Puccinia coronata f. sp. avenae race 320 was examined with the light microscope and the electron microscope. The scanning electron microscope revealed a network of ridges encircling the spines. On many urediniospores, small ring-like ridges, about 1 μ across, closely encircled the bases of the spines and sometimes were connected by fine linear ridges. On other spores, the ridges took the shape of four- to seven-sided polygons, 2–3 μ across, with triangles at their corners.