Several Pythium species causing leak on potato are managed by the systemic fungicide metalaxyl-M. Metalaxyl-M-resistant (MR) isolates of Pythium spp. have been identified in potato production areas of the U.S.A., but information is lacking on the distribution of MR isolates in the Pacific Northwest. Soil samples from numerous fields (312) cropped to potatoes in Idaho (140), Oregon (59), and Washington (113) were assayed using metalaxyl-Mamended agar for the presence of MR isolates of Pythium in 2004 to 2006. Altogether, 1.4%, 42.4% and 32.7% of the fields from these states, respectively, were positive for MR Pythium. Isolates of Pythium ultimum that were highly resistant to metalaxyl were recovered from 53 fields representing ID, OR, and WA. Greater than 50% of the Pythium soil population consisted of MR isolates in ten of 64 fields from Oregon and Washington. Nine species of Pythium were recovered from soil samples, of which MR P. ultimum and P. spinosum were identified. Isolates of MR P. ultimum recovered from soil were pathogenic on potato tubers and may pose a serious threat to the management of Pythium leak and seed rot of diverse crops rotated with potato.Resumen Varias especies de Pythium que causan la pudrición acuosa en papa son controladas por el fungicida sistémico metalaxilo-M. Cepas de metalaxilo-M-resistente (MR) de Pythium spp. han sido identificadas en áreas de producción de papa de los Estados Unidos, pero no hay información de la distribución de cepas MR en el Pacifico Noroeste. Muestras de suelo de numerosos campos (312) cultivados con papa, en Idaho (140), Oregon (59), y Washington (113) fueron ensayadas utilizando agar metalaxilo-M-enmendado para la presencia de Pythium MR del 2004 al 2006. En total, 1.4%, 42.4% y 32.7% de los campos de estos estados, respectivamente, dieron positivo a Pythium MR. Cepas de Pythium ultimum altamente resistentes al metalaxilo fueron recuperadas de 53 campos representando a Idaho, Oregon y Washington. Más del 50% de la población de Pythium del suelo, consistió de cepas MR en 10 de los 64 campos de Oregon Am.

With the recent report of several viruses infecting garlic (Allium sativum L.) grown in the Pacific Northwest (1–3), studies were initiated on cloves planted in the fall of 2006 to determine the presence of additional viruses infecting plants exhibiting mosaic and/or chlorotic leaves. Cloves from symptomatic plants of the cultivar ‘Early’ from two seed production fields in Benton County, WA and two seed production fields in Morrow County, OR were tested by two-step reverse transcription (RT)-PCR using primers specific to the coat protein (CP) of the allexiviruses (4), since garlic infected with this group had similar symptoms in Asia and South America (4). Of the 87 cloves tested, 84 were positive, and four representative samples of the RT-PCR amplicons from each location were cloned and sequenced. Sequence comparisons indicated that the cloves from both locations were infected with Garlic virus D (GarV-D), also known as Japanese garlic virus (JGV), since they shared 98% identity with known isolates (GenBank Accession Nos. L388922.1, AF519572.1, and AB010303.1). In addition, sequences of isolates from the Oregon cloves shared a 96% identity with a known isolate of Garlic virus B (GarV-B; GenBank Accession No. AF543829.1). Because no antiserum specific to these viruses was available, primers specific to the CP genes of GarV-D (JGV-F2/JGV-R2 5′-GCTCACTCRGATGTGTTAGC-3′ and 5′-CGCGTGGACATAAGTTGTTG-3′) and GarV-B (GVB-F1/GVB-R2 5′-GAGGAGAACTAACGCCACAC-3′ and 5′-ACGACCTAGCTTCCTACTTG-3′) were designed and the cloves were retested by RT-PCR using these virus-specific primers. With the GarV-D specific primers, 98 and 63% of the cloves were positive from Washington and Oregon, respectively, and 52% of the cloves from Oregon were positive using the GarV-B specific primers. None of the cloves tested from Washington were positive for GarV-B. The identity of the amplicons was verified by cloning and sequencing (GarV-D, GenBank Accession No. FJ643476; GarV-B, GenBank Accession No. FJ643475). Incidence of the two viruses differed between Oregon and Washington was likely due to the expansion of the seed lots in two different locations (California and Nevada) prior to planting in 2006. With such high infection rates, studies should be conducted to determine the impact of these viruses on yield when plants are singly infected as well as in combination with the other viruses known to infect garlic in this region. These and the other viruses (1) are likely to impact yield. To our knowledge, this is the first report of GarV-D (JGV) and GarV-B in garlic in the Pacific Northwest. References: (1) S. L. Gieck et al. Plant Dis. 91:461, 2007. (2) H. R. Pappu et al. Plant Dis. 89:205, 2005 (3) H. R. Pappu et al. Online publication. doi:10.1094/PHP-2008-0919-01-RS. Plant Health Progress, 2008. (4) T. Tsuneyoshi et al. Phytopathology 86:253, 1996.

Potato is the fourth most important agricultural commodity in Michigan and is grown for table stock, chip processing, and seed. Tubers are either processed or fresh packed immediately following harvest or sent to storage. Tubers of potato cv. FL1879 representing two separate fields in Huron County were removed from separate storage facilities in February and March of 2007, and substantial internal necrosis was observed in 1 to 2% of the tubers. Symptoms included arcs similar to those caused by Tobacco rattle virus (TRV). This virus is a member of the genus Tobravirus and is transmitted by a number of species of stubby-root nematodes (Paratrichodorus or Trichodorus spp.). Stubby-root nematodes have been reported previously from Michigan (1). To confirm the presence of TRV, nucleic acid extractions were made from these symptomatic tubers (3). Samples were initially tested for TRV by reverse transcription (RT)-PCR using primers specific to the 16 kDa open reading frame on genomic RNA-1 (2). Samples from both storage facilities were positive. The 463-bp RT-PCR product, amplified with these primers, was sequenced (GenBank Accession No. EU315227) and was 99.6% identical to the corresponding region of two TRV isolates from Florida and Washington (GenBank Accession Nos. AF055912 and EU315226, respectively). In addition, sap from cv. FL1879 tuber samples was used to transmit the virus mechanically to tobacco cv. Samsun NN, which produced typical TRV symptoms following inoculation, and sap extracts from the tobacco leaves also tested positive with antiserum specific to TRV upon subsequent ELISA testing. Corky ringspot can result in substantial losses, with entire potato fields being rejected because of internal tuber damage. Once found, fields must be considered permanently at risk to this disease due to the large host range of both the virus and the nematode vector. This disease has been previously found in the United States in California, Colorado, Florida, Idaho, Washington, Oregon, and it is likely present in Indiana. To our knowledge, this is the first report of corky ringspot and TRV on potato in Michigan. References: (1) G. W. Bird and N. Knobloch. Plant Dis. Rep. 60:76, 1976. (2) J. M. Crosslin and P. E. Thomas. Am. Potato J. 72:605, 1995. (3) G. G. Presting et al. Phytopathology 85:436, 1995.

In vitro dose responses of several calcium and potassium salts were determined on some commercially significant plant pathogens, including: Helminthosporium solani, Fusarium oxysporum f. sp. pisi race 2, Colletotricum coccodes, Phytophthora cactorum, Phytophthora cinnamomi, Phytophthora erythroseptica, Phytophthora infestans, Phytophthora megasperma, Pythium ultimum, and Venturia inaequalis. Mycelial growth inhibition was both salt-specific and dose-related. Pythium ultimum was completely inhibited by 75 mg·L−1 or greater calcium propionate, but needed 300 mg·L−1 or greater of calcium acetate and 40 mL·L−1 or greater of potassium silicate for complete inhibition. Phytophthora infestans was completely inhibited by 150 mg·L−1 or greater calcium acetate, 150 mg·L−1 or greater calcium propionate, or 5 mL·L−1 or greater potassium silicate. Phytophthora cactorum was completely inhibited by 300 mg·L−1 or greater calcium propionate, but required 600 mg·L−1 or greater calcium acetate and 10 mL·L−1 or greater potassium silicate for complete inhibition. Phytophthora cinnamomi was completely inhibited by calcium propionate at 600 mg·L−1 or greater or by 10 mL·L−1 or greater potassium silicate. Only potassium silicate inhibited Phytophthora megasperma, Phytophthora erthroseptica, V. inequalis, and H. solani at concentrations of 5 mL·L−1 or greater, 20 mL·L−1 or greater, 40 mL·L−1 or greater, or 80 mL·L−1 or greater, respectively. Potassium acetate did not completely inhibit any of the pathogens in this study when tested at concentrations 1200 mg·L−1 or less.

Research plots were established in 2004, 2005, and 2006 at Hermiston, Oregon and in 2005 and 2006 in Othello, Washington to determine if potato cultivars differ in current season PVY infection. Eight potato cultivars were used; Gem Russet, GemStar Russet, Russet Norkotah, Shepody, Alturas, Ranger Russet, Umatilla Russet and Russet Burbank. The first four listed produce mild symptoms due to current season infection with PVY. Cultivars were planted in a randomized complete block design with four replications where each block contained a single 50-hill row for each cultivar. Leaf samples were evaluated monthly via ELISA to follow naturally occurring PVY infection. Cultivars that produce mild symptoms had higher current season infection levels. Over the 3 years at Hermiston, Shepody (93.8%), Gem (92.8%), Gemstar (89.8%) and Russet Norkotah (82.7%) had the highest infection levels, while Russet Burbank (68.8%), Umatilla Russet (58.0%), Ranger Russet (49.6%) and Alturas (48.1%) had the least infection. At Othello, infection levels were much lower and cultivar differences were minimal though Gem Russet had the highest current season infection (30.4%), Ranger Russet had the lowest (4.9%) and was significantly lower than Gem Russet and Shepody. Higher levels of infection occurred in 2006 at Hermiston and Othello (77.1% and 18.2%, respectively) compared to 2005 (66.7% and 10.2%, respectively). This is the first report where different cultivars of potatoes, growing side by side, had different levels of PVY infection. Possible explanations for differing current season infection levels between cultivars are discussed. Resumen Se establecieron lotes experimentales en 2004, 2005, y 2006 en Hermiston, Oregon, y en 2005 y 2006 enOthello, Washington, para determinar si variedades de papa difieren en un ciclo en infección por PVY. Se utilizaron ocho variedades; Gem Russet, GemStar Russet, Russet Norkotah, Shepody, Alturas, Ranger Russet, Umatilla Russet y Russet Burbank. Las primeras cuatro de la lista producen síntomas ligeros debido a la infección por PVY en el mismo ciclo de cultivo. Las variedades se plantaron en un diseño de bloques completos al azar con cuatro repeticiones, donde cada bloque contenía un surco sencillo de 50 plantas por variedad. Se evaluaron mensualmente muestras de hoja con ELISA para seguir la infección natural por PVY que se fuera presentando. Las variedades que producen síntomas ligeros tuvieron los niveles de infección más altos durante el ciclo. En los tres años en Hermiston, Shepody (93.8%), Gem (92.8%), Gemstar (89.8%) y Russet Norkotah (82.7%), tuvieron los niveles mas altos de infección, mientras que Russet Burbank (68.8%), Umatilla Russet (58.0%), Ranger Russet (49.6%) y Alturas (48.1%) tuvieron la infección mas baja. En Othello, los niveles de infección fueron mucho mas bajos y