First Report of the White Pine Blister Rust Fungus (Cronartium ribicola) Infecting Whitebark Pine (Pinus albicaulis) and Ribes spp. in the Jarbidge Mountains of Northeastern Nevada

The Jarbidge Mountains are a remote and little-visited desert mountain range at the northern edge of the Great Basin in Elko County, NV, 110 km north of Elko and 115 km southwest of Twin Falls, ID. The forest is dominated by subalpine fir (Abies lasiocarpa) at lower elevations and whitebark pine (Pinus albicaulis) at higher elevations; limber pine (P. flexilis) occurs along streams in canyons at lower elevations (2). P. albicaulis and P. flexilis are hosts for the blister rust fungus, Cronartium ribicola. In the late 1990s, a survey across the Intermountain West reported no evidence of C. ribicola in the Jarbidge Mountains or elsewhere in the central Great Basin (3). However, unpublished observations by D. A. Charlet in 1988 and 2001 indicate that blister rust has been present in the Jarbidge Mountains for at least 16 years. In September 2002, D. R. Vogler visited the Jarbidge Mountains over a 2-week period, examining whitebark pines along the unpaved route through the Humboldt-Toiyabe National Forest connecting Highway 225 and Jarbidge, NV. Blister rust-infected whitebark were found in two locations: (i) Coon Creek Summit (2,575 m elevation), atop the divide between the Great Basin to the south and the Columbia Plateau to the north, and (ii) Bear Creek drainage (2,315 to 2,405 m elevation), 6.7 km northeast of Coon Creek Summit. At Coon Creek Summit, three whitebark pines ranging in diameter from 10 to 30 cm at breast height (dbh) were infected (evidenced by spindle-shaped branch swellings, aecia, and aeciospores), with the oldest infection occurring on wood produced in 1975. Assuming a mean needle retention of 10 years, the first pine infection likely occurred between 1975 and 1984. Ribes montigenum and an unknown Ribes sp. were common at Coon Creek Summit but were not infected. In the Bear Creek drainage north of the divide, 27 whitebark pines ranging in size from under 0.3 m high to 12 cm dbh were found infected, with the oldest infection on 1976 wood indicating an origin between 1976 and 1985. Most pines there, however, appeared to have been infected between 1994 and 1998. At Bear Creek, infection on Ribes spp. was common, with R. cereum the most frequently infected species. Voucher specimens of R. cereum (KPK-948 and KPK-949) are archived in the fungal herbarium at the Institute of Forest Genetics, Placerville, CA. On pine, fresh spermatia and aeciospores were abundant even though it was late in the season. Late sporulation has also been observed above 2,500 m on western white (P. monticola) and whitebark pine northeast of Lake Tahoe in Nevada (4). To our knowledge, our report marks the first recorded intrusion by C. ribicola into the north-central Great Basin. Recently, the first report of C. ribicola on Rocky Mountain bristlecone pine (P. aristata) was documented in southern Colorado (1). Now, Great Basin bristlecone (P. longaeva), which is restricted in Nevada to higher elevations in the eastern and southern parts of the state (2), may also be at risk; the northernmost occurrence of this last whitepine holdout from blister rust is in the Ruby Mountains, 135 km south of our findings in the Jarbidge Mountains. References: (1) J. T. Blodgett and K. F. Sullivan. Plant Dis. 88:311, 2004. (2) D. A. Charlet. Atlas of Nevada Conifers. University of Nevada Press, Reno, 1996. (3) J. P. Smith and J. T. Hoffman. Western North American Naturalist 60:165, 2000. (4) J. P. Smith et al. Plant Dis. 84:594. 2000.