Frequency of isolation, determination, and epidemiology of Alternaria species on potato in the Pacific Northwest

Many species of Alternaria have been isolated from potato, but only Alternaria solani and A. alternata have been described as pathogenic in the US. Isolations from early blight and brown spot type lesions on potato leaves collected in the Pacific Northwest were made between 2008 and 2011. Large-spored isolates were isolated less frequently than small-spored isolates. Pathogenicity of isolates was assessed on detached leaves of 'Russet Norkotah'. Phylogenetic species were distinguished with a restriction digest and 23 of 66 isolates were identified as A. alternata and 36 isolates as A. arborescens. No correlation was observed between pathogenicity and species (r= 0.12, P= 0.33). Seven isolates had no restriction site and were identified as A. oregonensis, A. arbusti, or A. metachromatica in section infectoria by sequencing.Aggressiveness of three Alternaria species was quantified on 'Russet Norkotah', four other potato varieties, and whole plants of `Russet Norkotah'. The effects of wounding were also evaluated. While wounding had a significant impact on mean infection frequencies (MIF) and area under the lesion expansion curve (AULEC) for A. alternata and A. arbusti, it did not affect MIF or AULEC of A. solani. AULEC of wholeplants was positively and significantly correlated with AULEC on detached leaves. Umatilla Russet was the most susceptible and Russet Alturas and Russet Burbank were the least susceptible cultivars for all three pathogen species.Fungicide resistance to azoxystrobin and boscalid is expected due to the specific modes of action of each fungicide. Prescreening at a threshold concentration was done to estimate the range of fungicide resistance of A. solani and A. alternata in the region. Growth ratios (GR) and percent spore germination (PSG) were evaluated. Only an increase in the resistance to boscalid by A. solani was observed between 2010 and 2011. Resistance of five isolates was then fully characterized at three concentrations of both fungicides. The lowest concentrations of fungicides were ineffective at reducing PSG or GR. In general, PSG of A. solani and A. alternata were not significantly reduced by the highest concentrations of either azoxystrobin or boscalid and as fungicide concentrations increased, mycelial growth decreased

Pseudomonas diseases on cucurbits in Western Washington

Cucurbits are well-suited for the maritime climate in western Washington and are considered high value specialty crops. For example, the most recent USDA NASS census data for pumpkins grown in Washington show that 398,000 cwt were produced with a value of $11,844,000 (USDA NASS 2019) in 2018. However, cucurbits are susceptible to a number of bacterial pathogens that can reduce fruit quality. One such group of bacterial pathogens is Pseudomonas syringae. Bacteria are microscopic, single-celled organisms, and Pseudomonas syringae are tiny rod-shaped organisms that are approximately 0.8 by 1–2 μM. Within this species are a number of pathovars, or strains, that cause similar symptoms on cucurbits

Puccinia areolata, P. treleasiana, and P. gemella on Marshmarigold (Caltha spp.) in subalpine habitats in Northwestern United States

Marshmarigolds (Caltha spp.) are members of the buttercup family (Ranunculaceae) and inhabit the Cascade and Rocky Mountains in western North America. Several rust species infect Caltha species, but only Puccinia areolata, Puccinia treleasiana, and Puccinia gemella have been reported in the Pacific Northwest. Observations were made on rust incidence and severity on Caltha spp. in July through September between 2001 and 2013 in subalpine regions of Colorado, Idaho, Montana, Utah, Washington and Wyoming. Leaves, petioles and flower stalks with rust pustules were examined and the host species identified using morphological characteristics. Plants collected in ID, WA, and MT were identified as Caltha leptosepala ssp. howelli (syn Caltha biflora) and plants in WY, CO, and UT were identified as Caltha leptosepala ssp. leptosepala. Foci of infection were typically solitary leaves, individual plants or small clusters of infected plants although a 90% incidence of infected rust plants was observed in a 10 m diameter area with no visually distinct foci in WA in 2013. Puccinia areolata was the only rust observed in Washington, Puccinia gemella was observed in Idaho, and Puccinia treleasiana was observed in Montana and Wyoming. Collections made possible direct comparisons among the three rust species