First Report of Gymnosporangium yamadae Causing Japanese Apple Rust on Crabapple (Malus spp.) in Ohio

Japanese apple rust, caused by the heteroecious and demicyclic rust fungus Gymnosporangium yamadae Miyabe ex G. Yamada, can affect juniper (Juniperus spp.), where the telial stage of this disease occurs, and apple or crabapple (Malus spp.), where the aecial stage occurs (Yun, 2010). Leaf samples displaying symptoms and signs of rust disease were collected in August 2020 from 14 different crabapple cultivars (‘Amerspirzam’ [American Spirit®], ‘Amsalzam’ [American Salute™], ‘Excazam’ [Excalibur™], ‘Guinzam’ [Guinevere®], ‘Hargozam’ [Harvest Gold®], ‘Mary Potter’, ‘Orange Crush’, ‘Prairie Maid’, ‘Professor Sprenger’, ‘Pumpkin Pie’, ‘Rawhide’, ‘Select A’ [Firebird®], ‘Shotizam’ [Show Time™], ‘Sinai Fire’) in the crabapple research plot of Secrest Arboretum (Crablandia) in Wooster, OH. Samples displayed adaxial leaf lesions with brown necrotic centers surrounded by a red-yellow coloration, corresponding on the abaxial side to lesions containing brown-orange aecia, producing aeciospores, surrounded by a dark red-orange coloration (Supplemental Figure 1). One to multiple lesions were present per symptomatic leaf. DNA was extracted from symptomatic leaf tissue containing fungal material on all 14 cultivars using the DNeasy Plant Mini Kit (QIagen) and the D1/D2 region of the 28S rDNA was amplified using primers NL1 and NL4 (O’Donnell 1993) according to Dagar et al. (2011). GenBank BLAST sequence analysis of all 14 sequences resulted in 99.83-100% sequence identity to G. yamadae with with 99% query coverage (MN605735). Sequences from all samples were deposited in GenBank under Accession Nos. MW131119.2-131125.2 and MW131127.2-131132.2. Morphological features were characterized for the three representative cultivars ‘Amerspirzam’ (American Spirit®), ‘Orange Crush’ and ‘Pumpkin Pie’ (Supplemental Figure 2). Aecia were hypophyllous, roestelioid, with cornute, yellow-brown, peridia with lacerate sides. Peridial cells appeared yellow and were long-linear rhomboid, verrucose with long papillae, smooth outer walls and echinulate inner walls, measuring 45 - 78 × 16 – 27 µm (average 65 × 21 µm), 51 - 82 × 16 – 30 µm (average 66 × 23 µm), and 47 – 93 × 14 – 31 µm (average 64 × 24 µm), respectively (n=50 per cultivar). Aeciospores were globose, 20 - 26 × 18 - 24 µm (average 23 µm × 20 µm), 21 - 28 µm × 19 - 24 µm (average 24 µm × 21 µm), and 21 - 27 µm × 18 - 23 µm (average 23 µm × 21 µm), respectively, with a slightly coronate surface and dark yellow walls 1.6 - 2.7 µm (average 2 µm), 1.4 - 2.4 µm (average 2 µm), and 1.3 - 2.5 µm (average 1.8 µm) thick, respectively (n=50 per cultivar). The telia, known to occur on Juniperus spp., were not observed. Specimens from these three cultivars were deposited into the U.S. National Fungus Collections (BPI 923889, 923888, 923887). Japanese apple rust has been officially reported in parts of Eastern Asia and the Eastern United States and is also known to be present in parts of Far East Russia and Ontario, Canada (Yun et al., 2009; CAB International, 2008). This report constitutes the first confirmed instance of G. yamadae causing Japanese apple rust in Ohio. Because infected trees tend to be highly symptomatic, this disease poses a significant threat to the nursery and landscape industries as it can decrease the market value of ornamental varieties and affect yield and crop quality in varieties used for fruit production.

Gymnosporangium przewalskii sp. nov. (Pucciniales, Basidiomycota) from China and its life cycle

In an investigation of rust fungi in Qinghai Province, northwestern China, the novel rust species Gymnosporangium przewalskii was identified based on morphology and phylogenetic analyses. Phylogenetic analyses using the internal transcribed spacers (ITS) and the large subunit (LSU) rRNA partial gene revealed that G. przewalskii is monophyletic and distinct from other Gymnosporangium species. The life cycle of this new taxon was clarified based on molecular data. Its spermogonial and aecial stages occurred on Sorbus koehneana, and its telial stage was found on Juniperus przewalskii.

First Report of the Telial Stage of Japanese Apple Rust on Juniperus chinensis in North America and the Aecial Stage on Malus domestica

Following a report in April 2009 of the presence of Gymnosporangium yamadae Miyabae ex G. Yamada on crabapple (Malus toringo Siebold) in Wilmington, DE (2), University of Delaware, State of Delaware, and USDA/APHIS PPQ personnel collaborated to confirm and document the pathogen. G. yamadae is the causal agent of Japanese apple rust. The fungus is known from Asia with an aecial state on economically important Malus species and telial state on Juniperus chinensis. During the April 2009 site visit, ornamental J. chinensis were observed near the original crabapples. On May 7, 2009, telial galls were collected from the ornamental J. chinensis at the Wilmington site. The telia were confirmed to be G. yamadae by morphometric analysis and molecular data. The rDNA large subunit (LSU) sequence derived from the collected telial galls (GenBank Accession No. GU058012) was identical to the eight G. yamadae LSU sequences (GenBank Accession Nos. FJ848760–FJ848765, FJ559373, and FJ559375) reported from Korea by Yun et al. (3). Teliospores were 45 to 54 μm long with pedicels that were wide (7.0 to 8.4 μm) along the full length. The G. yamadae telial gall collected from Wilmington, DE was deposited into the U.S. National Fungus Collection (BPI 879273). Leaves of M. domestica on the University of Delaware farm in Newark were confirmed to have Japanese apple rust on Aug 4, 2009. Identification was made on the morphological presence of unique roestelioid aecia with long cornulated peridia that lacerate along the sides. The aecia differ from those of G. juniperi-virginianae, the causal agent of cedar apple rust, which has aecial peridia that fimbriate to the base and are strongly recurved (1). Following release of a USDA Pest Alert, subsequent samples submitted to USDA/APHIS PPQ indicated widespread incidence of the G. yamadae aecial state in the northeast, including Maryland, Maine, New Hampshire, New Jersey, New York, Pennsylvania, and Rhode Island. Japanese apple rust likely went undetected for several years because of similar symptomatology to cedar apple rust. To our knowledge, this is the first report of the telial stage of G. yamadae in North America and the first report of this pathogen on Malus domestica in the United States. Knowledge of the geographic distribution of G. yamadae is of significance because of the actionable regulatory status of the pathogen and its potential impact on ornamental and fruit growers of Malus spp. in the United States. References: (1) F. D. Kern. A Revised Taxonomic Account of Gymnosporangium. Pennsylvania State University Press, University Park, PA, 1973. (2) H. Y. Yun et al. Plant Dis. 93:430, 2009. (3) H. Y. Yun et al. Mycologia 101:790, 2009.

First Report of Gymnosporangium sabinae, European Pear Rust, on Bradford Pear in Michigan

Bradford pear, Pyrus calleryana Decne., is well known as an ornamental plant for its flowers, leaf color in fall, and disease resistance, making it desirable as a street tree. In August and October of 2008, the aecial stage of Gymnosporangium sabinae (Dicks.) G. Winter was collected from leaves of P. calleryana in Farmington, MI (Oakland County). The one tree had foliage that was severely affected by the rust fungus. Using published descriptions of G. sabinae as the synonym of G. fuscum, type of the genus Gymnosporangium (1–4), the Michigan specimen was identified and confirmed by comparison with previously reported European and U.S. specimens (BPI 118736 and BPI 856578). The diagnostic characteristics of G. sabinae include: spermagonia epiphyllous; aecia hypophyllous, roestelioid, 3 to 6 mm high; peridium balanoid (acorn shaped), becoming elongated at maturity, pale yellow, sides opening with lateral slits but remaining attached at light brown, pointed apex; peridial cells elongated, 51 to 68 μm long, outer walls smooth, inner walls and side walls sparsely echinulate; aeciospores globose to broadly ellipsoid, somewhat angular, surface slightly coronate, 22 to 32 × 22 to 36 μm, walls orange, 3.5 to 5.5 μm thick. This species is distinguished from other species of Gymnosporangium on Pyrus by the balanoid (acorn-shaped) peridium and the late season maturation of the aecial stage (4). Telia and teliospores of G. sabinae are produced on the alternate host, various species of Juniperus sect. Sabinae, but were not observed in Michigan. The specimen from Michigan is deposited in the U.S. National Fungus Collections (BPI 878928). G. sabinae is widely distributed in Europe, extending to Asia and North Africa, but is rarely reported in North America. It was accidentally introduced into California in the aecial stage on P. communis L. and the telial stage on Juniperus chinensis L. (2), as well as introduced into Canada (British Columbia) (3,4). The only previous report of G. sabinae on P. calleryana is in Germany (1). G. sabinae is known to attack commercial pear and ornamental juniper plants in Europe, thus it seems important to prevent the further spread of this fungus in North America. References: (1) U. Braun. Feddes Repert. Beih. 93:213, 1982. (2) G. Laundon. Mycotaxon 3:133, 1975. (3) A. H. McCain and D. Y. Rosenberg. Calif. Dep. Agric. Bull. 50:13, 1961. (4) J. A. Parmelee. Fungi Canadensis No. 43. Gymnosporangium fuscum, 1974.

First Report of Uredo manilensis in the Western Hemisphere

Crepe jasmine, Tabernaemontana divaricata (L.) R. Br. ex Roem. & Schult. (Apocynaceae), is a popular flowering shrub in South Florida. A native of Southeast Asia, it is one of approximately 100 ornamental species in the genus. In December 2007, rust was observed on the leaves of landscape plants in Key West and Miami. The rust has become prevalent and severely affects young and old leaves of plants in the landscape and in commercial nurseries. Leaf lesions begin as chlorotic flecks that expand into necrotic spots with orange-to-reddish brown, subepidermal uredinia; brown telia develop on the abaxial side of leaves. Urediniospores are one-celled, initially hyaline, minutely echinulate and spherical, turn dark orange, and measure (22) 24 to 29 (32) × (19) 21 to 24 (26) μm. Teliospores are (26) 29 to 36 (38) × (20) 22 to 26 (28) μm, two-celled, ellipsoidal to ovoid, echinulate, constricted at the septum, reddish brown, and have 0.8-μm thick spore walls; pedicels are 25 × 5.6 μm, persistent, and hyaline. Attributes for urediniospores are consistent with those from the original description of Uredo manilensis Syd. & P. Syd. on T. coronariae in Manila (2); however, there are no reports of a telial stage for this rust. Attributes for urediniospores of the South Florida fungus were also consistent with those on herbarium specimens of U. manilensis from the U.S. National Fungus Collection, also collected in Manila but from T. polygama (BPI Accession Nos. 0155269 and 0155270). Notably, these specimens contained telia that matched those found in South Florida. Subsequent comparisons were made with herbarium specimens of the three Puccinia spp. that have been reported on Tabernaemontana spp. (the U.S. National Fungus Collection or the Arthur Herbarium, Purdue University, West Lafayette, IN). Puccinia engleriana (five specimens from India, New Guinea, and the Philippines) differs from the BPI specimens of U. manilensis and the South Florida fungus by its bigger teliospores (32) 35 to 41 (45) × (21) 22 to 24 μm. P. tabernaemontana (six specimens from Uganda) has bigger urediniospores ([45] 34 to 41 × [34] 26 to 32 μm) and yellow-brown, poorly echinulated to almost smooth teliospores. The revised material of P. morobensis (type) was poor, but according to the original description (1) and notes found in the herbarium specimen, the teliospores (24 to 29 × 33 to 45 μm) and urediniospores are larger (23 to 28 × 29 to 35 μm) and the teliospores walls are finely and sparsely echinulated to sometimes smooth, and the pedicels are very short and fragile. A specimen of the South Florida fungus was deposited with the U.S. National Fungus Collections (BPI Accession No. TBA). To our knowledge, this is the first report of U. manilensis in the Western Hemisphere and the first time a telial stage (provisionally P. manilensis) has been recognized for the fungus. This disease has become a concern in South Florida for gardeners as well as producers who must now treat the crop with fungicides. References: (1) G. B. Cummins. Mycologia. 33:148, 1941. (2) H. Sydow, and P. Sydow. Ann. Mycol. 8:36, 1910.

Occurrence of Telia of Phakopsora pachyrhizi on Kudzu in Texas

The first discovery of Asian soybean rust (ASR) caused by Phakopsora pachyrhizi H. Sydow & Sydow in the continental United States was in Louisiana in 2004 (3). In Texas, the uredial stage of this fungus was first found on kudzu (Pueraria lobata) in November 2005 and 3 months later on soybean (Glycine max) (2). The telial stage of P. pachyrhizi was first reported in the continental United States on kudzu in central Florida (1). On January 5, 2008, telia of P. pachyrhizi along with uredia were found on living kudzu leaves at two locations in Polk and Liberty counties of East Texas, where only the uredial stage had been found in September of 2007. The kudzu in both locations had died back more than 99% in January. A single telium or a cluster of telia were found along with uredinia on the abaxial leaf surface. Telia and uredinia (n = 20) were similar in size, 136.3 ± 26.3 and 133.1 ± 16.4 μm in diameter, respectively. Telia were dark brown to black compared with tan colored uredinia. Elongated, oval-shaped teliospores (n = 15) were 18.1 ± 1.7 μm long and 10.6 ± 1.0 μm wide. A reexamination of herbarium specimens from previous ASR collections indicated that telia had been present on kudzu leaves from Liberty County collected in December of 2005 and 2006. In contrast, telia were not found on soybean leaves collected in February of 2006 and 2007 and January of 2008 from Hidalgo County in the Lower Rio Grande Valley (LRGV), an area with a subtropical climate where ASR hosts could survive year round. Kudzu does not occur in the LRGV. Infected kudzu in East Texas can support production of telia over the winter months. However, the hosts that can be infected by basidiospores have not been identified, and so the significance of telia as a source of genetic variation is not known. To our knowledge, this is the first report of the telial stage of P. pachyrhizi in Texas. References: (1) C. L. Harmon et al. Plant Dis. 90:380, 2006. (2) T. Isakeit et al. Plant Dis. 90:971, 2006. (3) R. W. Schneider et al. Plant Dis. 89:774, 2005.

First Report of Phakopsora pachyrhizi Telia on Kudzu in the United States

Soybean rust caused by Phakopsora pachyrhizi H. Sydow & Sydow was first reported in the continental United States during 2004 (2). By 10 November 2005, the disease was confirmed in eight southern states (Florida, Georgia, Alabama, Mississippi, South Carolina, North Carolina, Louisiana, and Texas). Diagnoses have been based on visual observation of uredinia and urediniospores of the pathogen followed by polymerase chain reaction confirmation. On 10 November 2005, uredinia and telia were identified on leaves of kudzu (Pueraria lobata) in central Florida. Telia first were noted as dark brown-to-black flecks on the abaxial leaf surface intermingled with abundant tan-to-light brown uredinia. Of 200 leaves examined, 143 (72%) had telia. The number of telia ranged from a few (1/cm2) that were scattered to many (73/cm2). Telia were approximately the same diameter as uredinia, but were appressed to the leaf surface and pigmented. Twenty telia were excised from host tissue with the aid of a dissecting microscope and a 20 gauge hypodermic needle. Telia averaged 89 × 100 μm (n = 20, σ = 17 and 16 μm, respectively). Four telia were crushed and five teliospores from each averaged 4.3 × 8.3 μm (n = 20, σ = 0.5 and 0.9 μm, respectively). Pale yellowish brown-to-hyaline teliospores were similar in color to urediniospores. Observations matched descriptions by Ono et al. (1). To our knowledge, this is the first report of the telial stage of P. pachyrhizi in the United States. References: (1) Y. Ono et al. Mycol. Res. 96:825, 1992. (2) R. W. Schneider et al. Plant Dis. 89:774, 2005.

Asian Soybean Rust: Incidence, Severity, and Morphological Characterization of Phakopsora pachyrhizi (Uredinia and Telia) in Argentina

Asian soybean rust (ASR), caused by Phakopsora pachyrhizi, is the most destructive disease of soybean (Glycine max) in many areas of the world. ASR was first detected in Argentina during 2002 in a limited area in the northern region of the country (2). During the 2004 growing season, P. pachyrhizi spread rapidly throughout most soybean growing areas of northwestern and northeastern Argentina. ASR was also was found in some fields in Entre Ríos and Santa Fe provinces. In all areas, symptoms were expressed late in the 2004 season (growth stages R5.5 to R7) and yield losses were minimal. The objectives of this study were to quantify P. pachyrhizi infection in the canopy and morphologically characterize the fungus from fields where it had been previously detected by polymerase chain reaction (PCR) (3). Incidence (percentage of plants affected) and severity (percentage of leaf area affected, including chlorosis) were visually estimated for 10 plants arbitrarily collected (April 2004) from each of three fields located in Charata (Chacabuco), Chaco Province (Sample 1, collected in the R6 stage), La Paloma (Moreno), Santiago del Estero Province (Sample 2, stage R6 to R7), and Tolloche (Anta), Salta Province (Sample 3, stage R5.5). Disease assessments were made for the lower, middle, and upper canopy from 15 leaves per plant. The number of pustules per cm2 and uredinia per lesion were recorded from the undersides of central leaflets for each trifoliolate observed. Tissue sections were made to observe fructifications of P. pachyrhizi. Incidence of affected plants was 100% in all fields. Disease severity for Sample 1 was 45% (range 30 to 60%), 20% (10 to 30%), and 10% (5 to 20%) for the lower, middle, and upper canopy, respectively; for Sample 2: 60% (30 to 80%), 40% (25 to 50%), and 25% (15 to 40%) for the lower, middle, and upper canopy, respectively; and for Sample 3: 25% (10 to 50%), 15% (10 to 20%), and 10% (5 to 15%) for the lower, middle, and upper canopy, respectively. The number of pustules per cm2 for Sample 1 was 156/cm2 (range 88 to 200); Sample 2: 172/cm2 (128 to 232); and Sample 3: 120/cm2 (72 to 232). The number of uredinia per lesion for Sample 1 was 6 per lesion (range 1 to 15); Sample 2: 5.5 per lesion (1 to 13), and Sample 3: 2.8 per lesion (1 to 5). The two spore types that were commonly observed were urediniospores and teliospores. Telia were found on infected leaves mixed with uredinia in every sample. Urediniospores measured 16 to 22 μm (mean 18.5 μm) × 25 to 30 μm (mean 27 μm). Teliospores measured 8 to 11 μm (mean 9 μm) × 19 to 27 μm (mean 23.8 μm). Spores sizes are in the range described by Ono et al. (1). To our knowledge, this is the first report of epidemiological and morphological characterization of ASR in Argentina and the first report of the telial stage of P. pachyrhizi on soybean in South America. References: (1) Y. Ono et al. Mycol. Res. 96:825, 1992. (2) R. L. Rossi. Plant Dis 87:102, 2003. (3) SINAVIMO, Sistema Nacional Argentino de Vigilancia y Monitoreo de plagas. Roya de la soja: Resultados de la campaña 2003-2004. On-line publication. SENASA, 2004.

First Report of the Telial Stage of Gymnosporangium exiguum on Ashe Juniper Adjacent to Hawthorn with Rust in Southwest Texas

The telial stage of Gymnosporangium exiguum (2) on Ashe juniper (Juniperus ashei) was observed in Bandera County, TX, in April and May 1999 after rain events. Symptomatic plants with multiple lesions were found at low frequencies in dense J. ashei populations. Orange telia formed on scales and bark and on 2- to 3-mm-diameter twigs and became nearly inconspicuous when dry. No hypertrophy was observed. Previously reported telial hosts include J. californica and J. excelsa cv. Stricta in California; J. mexicana and J. scopulorum in Oklahoma; J. virginiana in Texas; and J. deppeana var. pachyphloea in Oklahoma and Texas (1). An aecial stage identified as G. exiguum has been observed for many years on native hawthorns (Crataegus crus-galli, C. greggiana, C. mollis, C. stevensiana, C. tracyi, C. turnerorum, C. viridis var. desertorum, and several natural hybrids) in Bandera, Bexar, Edwards, Gillespie, Kendall, Kimble, Real, and Uvalde counties, Texas. Prominent roestelioid aecia were observed on hawthorn leaves, petioles, fruits, peduncles, thorns, and, less often, on twigs. In two experimental plantings of hawthorns in Bandera County, rust severity was rated as low to moderate in six populations of C. greggiana and hybrids; moderate in two populations each of C. stevensiana and C. tracyi; moderate to severe in three populations of C. crus-galli and hybrids; and severe in one population each of C. mollis and C. viridis var. desertorum. G. exiguum was previously reported on a Crataegus sp. in Texas and on Heteromeles arbutifolia in California (1). Flowers, fruits, plant forms, and drought tolerances are characteristics of some endemic hawthorns that provide landscape and wildlife advantages. G. exiguum causing rust disease may limit the ornamental potential of highly susceptible hawthorn species in southwest Texas. Inconspicuous infections on susceptible ornamental Juniperus spp. also could have phytosanitary implications. Voucher specimens (aecia and telia) are on deposit in the Mycological Herbarium, Department of Plant Pathology, North Carolina State University, Raleigh. References: (1) D. F. Farr et al. 1989. Fungi on Plants and Plant Products in the United States. The American Phytopathological Society, St. Paul, MN. (2) F. D. Kern. 1973. A Revised Taxonomic Account of Gymnosporangium. The Pennsylvania State University Press, University Park.