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Since 2018, bleeding cankers have been observed on maple trees in multiple home gardens in southwest Idaho. The cankers ooze a dark sap and and are approximately 10 cm to 35 cm in diameter. Cankers typically occur on the main trunk but are also present on scaffold branches in severe infecrions. Symptoms of foliar chlorois, branch dieback, and premature autumn senescence were also associated with the disease. Phytophthora DNA was detected in symptomatic material from five trees using real-time PCR (Miles et al., 2017). In July 2019 recovery of a causal agent from a symptomatic Acer x freemanii tree was attempted. Excisions were made from the interface of healthy and diseased tissue around the cankers using a chisel. The tissue was then placed in sealed plastic ziplock bags at 4°C for 7 days. Hyphae were then removed with forceps and placed onto potato dextrose agar (PDA) amended with penicillin G (0.2 g/liter) and streptomycin sulfate (0.8 g/liter). Colonies resembling Phytophthora cactorum were consistently observed after 5 days at 21°C. Tentative P. cactorum identification was based on the presence of abundant papillate and caducous sporangia on a short pedicel; sporangia were approximately 30 μm long and 26 μm wide (Bush et al., 2006; Hudler, 2013). Individual hyphal tips were transferred to fresh PDA plates and sequencing of both the rDNA ITS region and Cytochrome c oxidase subunit I (COI) was completed for a representative isolate (D19-130). DNA extraction, PCR and sequencing were as previously described (Woodhall et al. 2013; Robideau et al., 2011). The resulting DNA sequences for rDNA ITS (MW315449) and COI (MW881040) were both 100% identical (723/723 bp and 728/728 bp) with sequences from cultures previously identified as P. cactorum (MH171627 and MH136858). To determine pathogenicity, 14 month-old maple (A. x freemanii) trees in individual containers with potting mix were wounded 15 mm above the soil line with a single 10 mm incision using a sterile razor blade and inoculated by placing a 10 mm2 fully colonized PDA plug of isolate D19-130 on the wound. The inoculum and wound were then covered with a damp cotton ball that was secured loosely with parafilm. Control plants consisted of uninoculated plants and wounded plants inoculated with a PDA agar plug. Each treatment was replicated five times and placed in a controlled environment chamber set at 24ºC and 90% relative humidity. All treatments were sprayed with water daily to ensure the cotton balls remained damp. After 8 weeks, black lesions, up to approximately 25 mm above the soil line, were observed on the stem base of all P. cactorum-inoculated plants. No black lesions were observed on non-inoculated plants or plants inoculated with a PDA agar plug. P. cactorum was isolated from lesions, as described above, except polystyrene foam boxes containing moist paper towels were used instead of bags. This report confirms P. cactorum as a causal agent of bleeding canker of maple in Idaho for the first time. It has been shown that several Phytophthora species can infect maple (Jung and Burgess, 2009; Huddler, 2013). P. cactorum has a wide host range but certain strains have been associated with lethal bleeding stem cankers in maple and other deciduous trees worldwide (Huddler, 2013). Knowledge of the causal agent of bleeding canker on maple will help determine appropriate disease management practices.

A survey of the relative incidence of anastomosis groups (AG) of Rhizoctonia spp. associated with potato disease was conducted in Idaho, the leading potato producing state in the USA. In total, 169 isolates of Rhizoctonia solani and seven binucleate Rhizoctonia (BNR) isolates were recovered from diseased potato plants. The AG of each isolate was determined through real-time PCR assays for AG 3-PT and phylogenetic analysis of the internal transcribed spacer region of ribosomal DNA. AG 3-PT was the predominant AG accounting for 85% of isolates recovered, followed by AG 2-1 (5.7%) and AG 4 HG-II (4.5%). Two different subsets of AG 2-1 isolates were recovered (subset 2 and 3). Three isolates each of AG A and AG K were recovered, as well as one isolate each of AG 5 and AG W. An experiment carried out under greenhouse conditions with representative isolates of the different AGs recovered from Idaho potatoes showed differences in aggressiveness between AGs to potato stems, with AG 3-PT being the most aggressive followed by an isolate of AG 2-1 (subset 3). The three BNR isolates representative of AG A, AG K and AG W appeared to be less aggressive to potato stems than the R. solani isolates except for the AG 2- 1 (subset 2) isolate. This is the first comprehensive study of the relative incidences of Rhizoctonia species associated with Idaho potatoes and the first study to report the presence of BNR AG W outside of China.

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