First Report of Rust Caused by Puccinia similis on Artemisia tridentata in Idaho and Oregon.

Artemisia tridentata Nutt. (Asteraceae), commonly called sagebrush or big sagebrush, is a coarse, hardy, silvery-gray bush growing in arid sections of the Great Basin Desert of intermountain plateau covering portions of California, Idaho, Nevada, Oregon, Utah, and Wyoming in the western United States. Sagebrush is a key component of these ecosystems, providing canopy cover, nesting habitat, and a food source for numerous species of small animals and birds (4). During a plant disease survey in the Treasure Valley Region of southwestern Idaho and eastern Oregon, symptoms and signs of rust were observed on leaves of sagebrush in July 2007. Ten of fifteen plants (~70%) observed at the site were infected. Leaf samples of sagebrush with rust were also collected from a hedge in a home garden in Canyon County, ID in May 2006 and September 2007. Symptoms on both samples included cinnamon-brown, raised uredinia, primarily on the adaxial leaf surfaces. Initially, sori were scattered, increasing in density and becoming confluent. Urediniospores were thick walled, subglobose to obovoid, golden brown, echinulate, with three +/- equatorial germ pores, and measured 28 to 32 × 23 to 27 µm. Telia appeared late in the season (July to August) and were mostly scattered, becoming confluent and forming raised, ovoid, brown-to-dark red streaks on leaves and stems. Teliospores were brown to dark red, two-celled, averaging 45 × 26 µm, thick walled (average 0.75 to 1.5 µm), thickening at the apex, ellipsoid to broadly ellipsoid, with thin-walled, hyaline pedicels, 26 to 31 µm broad at attachment, tapering below, equal to or up to twice as long as the spore. On the basis of morphology, this pathogen was identified as Puccinia similis Ellis & Everh. (2), an autoecious rust previously reported from Arizona and Wyoming on A. tridentata and A. nova A. Nels. (3). To confirm the identification of the specimens from Idaho, an ~1,000 bp of DNA from the ribosomal 28S large subunit was amplified and sequenced with rust-specific primers (1) (GenBank No. GU168942). Since there are no sequences of P. similis available in GenBank for comparison, a sequence of the same gene was also obtained from a specimen of P. similis that had been collected on A. cana Pursh in Utah in 1995 by C. T. Rogerson and deposited in the U.S. National Fungus Collections (BPI 863644; GenBank No. GU168943). The sequences shared 100% identity and did not match any other species of rust in GenBank. To our knowledge, this is the first report of P. similis in Idaho and Oregon on sagebrush, and the first report, based on herbarium data, of this rust on A. cana in Utah. Voucher specimens from Idaho have been deposited in BPI (878064) and the Bernard Lowy Mycological Herbarium (LSUM). References: (1) M. C. Aime. Mycoscience 47:112, 2006. (2) G. B. Cummins. Rust Fungi on Legumes and Composites in North America. University of Arizona Press, Tucson, 1978. (3) D. F. Farr et al. Fungal Databases. Systematic Botany and Mycology Laboratory, Online publication. USDA-ARS, 8 July 2009. (4) B. L. Welch and C. Criddle, USDA Forest Service Res. Pap. RMRS-RP-40. 2003.

First Report of Powdery Mildew Caused by Leveillula taurica on Giant Blazing Star (Mentzelia laevicaulis).

Mentzelia laevicaulis (Dougl. ex Hook.) Torr. & Gray (Loasaceae; common names are giant blazing star and smoothstem blazing star) is widely distributed throughout western North America in sites ranging from lowland deserts to mountainous areas in Canada and the United States. During a plant disease survey in June 2007 in the Owyhee Mountains, Canyon County, Idaho, leaves of M. laevicaulis displaying whitish, mycelial growth were collected from plants growing on stream banks and gravelly road embankments. Diseased leaves exhibited localized, chlorotic discolorations associated with signs of a powdery mildew. Of approximately 20 plants at the site, 50% were infected. White mycelia and conidia were more abundant on the adaxial leaf surfaces than on the abaxial surfaces. Severely diseased leaves were buckled and slightly twisted. By August and through September, sporulation was greatest on mature plants, and lowermost leaves were completely covered with flocculose, dense, white mycelia. Dimorphic conidia were lanceolate or cylindrical and measured (44-) 46 to 67 (-71) × (14-) 14.5 to 20 (-21) µm. DNA was extracted and PCR was used to amplify the internal transcribed spacer (ITS) region as described previously (2), except that primers ITS 5 and P3 (4) were used. The resulting 633-bp sequence (GenBank Accession No. GQ860947) included a 616-bp region identical to a sequence reported previously for Leveillula taurica (Lév.) Arnaud from eastern Washington (GenBank No. AY912077), as well as ITS regions from L. taurica previously reported from Iran (GenBank No. AB048350) (2) and Australia (GenBank No. AF 073351) (2). Based on the ITS sequence, the present fungus grouped within Khodaparast et al. (3) Clade 1 that included L. taurica strains they distinguished from other, superficially similar species of Leveillula. On the basis of morphological and sequence data, the fungus was determined to be L. taurica (1,3). A voucher specimen was deposited in the Mycology Herbarium (WSP) at Washington State University. To our knowledge, this is the first report of a named powdery mildew species from a member of the Loasaceae. The only previous report of a powdery mildew on a loasaceous host was an undetermined Oidium sp. on a species of Mentzelia (1). The discovery of L. taurica on a previously unknown native host species is further evidence that this introduced pathogen is becoming endemic to the Pacific Northwest. Native host species, such as M. laevicaulis, may play a role in the epidemiology of powdery mildew diseases caused by L. taurica on crop and ornamental species in the Pacific Northwest. References: (1) U. Braun. Beih. Nova Hedwigia 89:1, 1987. (2) D. A. Glawe et al. Mycol. Prog. 4:291, 2005. (3) S. A. Khodaparast et al. Mycol. Res. 105:909, 2001. (4) S. Takamatsu and Y. Kano. Mycoscience 42:135, 2001.

First Report of Natural Infection of Penstemon acuminatus with Cucumber mosaic virus in the Treasure Valley Region of Idaho and Oregon.

Penstemons are perennials that are grown for their attractive flowers in the United States. Penstemon species (P. acuminatus, P. deustus, and P. speciosus) are among the native forbs considered as a high priority for restoration of great basin rangelands. During the summer of 2008, symptoms of red spots and rings were observed on leaves of P. acuminatus (family Scrophulariaceae) in an experimental trial in Malheur County, Oregon where the seeds from several native forbs were multiplied for restoration of range plants in intermountain areas. These plants were cultivated as part of the Great Basin Native Plant Selection and Increase Project. Several native wildflower species are grown for seed production in these experimental plots. Plants showed red foliar ringspots and streaks late in the season. Fungal or bacterial infection was ruled out. Two tospoviruses, Impatiens necrotic spot virus and Tomato spotted wilt virus, and one nepovirus, Tomato ring spot virus, are known to infect penstemon (2,3). Recently, a strain of Turnip vein-clearing virus, referred to as Penstemon ringspot virus, was reported in penstemon from Minnesota (1). Symptomatic leaves from the penstemon plants were negative for these viruses when tested by ELISA or reverse transcription (RT)-PCR. However, samples were found to be positive for Cucumber mosaic virus (CMV) when tested by a commercially available kit (Agdia Inc., Elkhart, IN). To verify CMV infection, total nucleic acid extracts from the symptomatic areas of the leaves were prepared and used in RT-PCR. Primers specific to the RNA-3 of CMV were designed on the basis of CMV sequences available in GenBank. The primer pair consisted of CMV V166: 5' CCA ACC TTT GTA GGG AGT GA 3' and CMV C563: 5' TAC ACG AGG ACG GCG TAC TT 3'. An amplicon of the expected size (400 bp) was obtained and cloned and sequenced. BLAST search of the GenBank for related sequences showed that the sequence obtained from penstemon was highly identical to several CMV sequences, with the highest identity (98%) with that of a sequence from Taiwan (GenBank No. D49496). CMV from infected penstemon was successfully transmitted by mechanical inoculation to cucumber seedlings. Infection of cucumber plants was confirmed by ELISA and RT-PCR. To our knowledge, this is the first report of CMV infection of P. acuminatus. With the ongoing efforts to revegetate the intermountain west with native forbs, there is a need for a comprehensive survey of pests and diseases affecting these plants. References: (1) B. E. Lockhart et al. Plant Dis. 92:725, 2008. (2) D. Louro. Acta Hortic. 431:99, 1996. (3) M. Navalinskiene et al. Trans. Estonian Agric. Univ. 209:140, 2000.

Identification of New Alternative Weed Hosts for Iris yellow spot virus in the Pacific Northwest.

Iris yellow spot virus (IYSV; family Bunyaviridae, genus Tospovirus) is an economically important viral pathogen of onion bulb and seed crops in several parts of the United States and the world (1). IYSV is primarily transmitted by onion thrips (Thrips tabaci) and there is no evidence of seed transmission (1). However, susceptible cultivated and weed species could serve as reservoirs of inoculum from which thrips could acquire the virus to introduce and spread it in onion fields. Samples from asymptomatic and symptomatic volunteer onion plants in some of the commonly cultivated crops in the region (corn, wheat, grapes, mint, carrot, alfalfa, and sugar beets) and several common weeds in and around onion bulb and seed fields with a history of IYSV in Idaho and Washington were collected during the months of July, August, September and October of 2006. More than 175 samples from 35 plant species were analyzed for IYSV by a commercially available ELISA kit (Agdia Inc., Elkhart, IN). With the exception of a few volunteer onions, none of the other plant species had any symptoms of virus infection. Symptoms on volunteer onions included characteristic diamond-shaped lesions. To confirm the presence of IYSV in the ELISA-positive samples, total nucleic acids were extracted (2) and used in a reverse transcription (RT)-PCR assay (3). The primer pair consisted of 5'-TAA AAC AAA CAT TCA AAC AA-3' and 5'-CTC TTA AAC ACA TTT AAC AAG CAC-3'. This primer pair flanks the nucleocapsid (N) gene of IYSV and generates an approximate 1.2-kb amplicon (3) that includes the complete N gene. An amplicon of expected size was obtained from each IYSV-positive sample. The amplicons were cloned and sequenced. There was a 95% sequence identity with known IYSV sequences. While several weed species gave ELISA values that suggested the presence of IYSV, results of RT-PCR assays failed to confirm the presence of the virus. This discrepancy between ELISA and RT-PCR results could be due to nonspecific reaction in ELISA (4) or difficulty associated with obtaining RT-PCR-quality templates for amplification. Only volunteer onions and the following weeds tested positive for IYSV by ELISA and RT-PCR: redroot pigweed (Amaranthus retroflexus), puncturevine (Tribulus terrestris), kochia (Kochia scoparia), prickly lettuce (Lactuca serriola), and common lambsquarters (Chenopodium album). Of these, redroot pigweed was recently reported to be ELISA-positive for IYSV (1). This information on the wider natural host range of IYSV, including potential alternative hosts that could serve as virus reservoirs, is useful for a better understanding of the disease epidemiology and in developing an integrated management strategy for reducing the impact of this disease. References: (1) D. Gent et al. Plant Dis. 90:1468, 2006. (2) H. R. Pappu et al. HortScience 40:697, 2005. (3) H. R. Pappu et al. Arch. Virol. 151:1015, 2006. (4) T. N. Smith et al. Plant Dis. 90:729, 2006.