First Report of the White Pine Blister Rust Pathogen, Cronartium ribicola, in Arizona.

White pine blister rust, caused by Cronartium ribicola J.C. Fisch., was found on southwestern white pine (Pinus flexilis James var. reflexa Engelm., synonym P. strobiformis Engelm.) near Hawley Lake, Arizona (Apache County, White Mountains, 34.024°N, 109.776°W, elevation 2,357 m) in April 2009. Although white pines in the Southwest (Arizona and New Mexico) have been repeatedly surveyed for blister rust since its discovery in the Sacramento Mountains of southern New Mexico in 1990 (1,2), this was the first confirmation of C. ribicola in Arizona. Numerous blister rust cankers were sporulating on 15- to 30-year-old white pines growing in a mixed conifer stand adjacent to a meadow with orange gooseberry bushes (Ribes pinetorum Greene), a common telial host in New Mexico. Most of the observed cankers were producing their first aecia on 5-year-old branch interwhorl segments (i.e., formed in 2004). The two oldest cankers apparently originated on stemwood formed about 14 and 21 years before (1995 and 1988). Neither uredinia nor telia were seen on expanding gooseberry leaves in late April, but these rust structures were found later in the season. Voucher specimens deposited in the Forest Pathology Herbarium-Fort Collins (FPF) were determined by host taxa and macro- and microscopic morphology as C. ribicola-white pine with typical cankers, aecia, and aeciospores (1). Six collections of aeciospores from single, unopened aecia provided rDNA sequences (ITS1-5.8S-ITS2, primers ITS1F and ITS4) with two different repeat types (GenBank Accession Nos. HM156043 and HM156044 [J. W. Hanna conducted analysis with methods described in 3]). A BLASTn search with these sequences showed 100 and 99% similarities, respectively, with sequences of C. ribicola, including accessions L76496, L76498, and L76499 from California (4). Additional reconnaissance of white pines on the Fort Apache Indian Reservation and neighboring Apache-Sitgreaves National Forests was conducted from May through September 2009. Although the blister rust infestation was distributed over more than 100 km2 of forest type, infected trees were restricted to mesic and wet canyon bottoms (climatically high-hazard sites) and were not found on dry sites-even where aecial and telial hosts occurred together. Recent dispersal within the White Mountains was suggested by a presence of infected gooseberry plants on several sites where infected white pines were not yet evident. Geils et al. (1) concluded that the initial infestation in New Mexico had originated by long-distance, aerial transport from California to the Sacramento Mountains in 1969. Since then, numerous additional infestations in the Southwest have been discovered; but we do not know which of these (including Arizona) resulted by dispersal from California or New Mexico. Although rust may eventually infest many host populations in the Southwest and disease may kill most trees in some locations, differences in site hazard and spread provide managers with numerous opportunities to maintain white pines and Ribes spp. References: (1) B. Geils et al. For. Pathol. 40:147, 2010. (2) F. Hawksworth. Plant Dis. 74:938, 1990. (3) M.-S. Kim et al. For. Pathol. 36:145, 2006. (4) D. Vogler and T. Bruns. Mycologia 90:244, 1998.

Influence of host resistance on the genetic structure of the white pine blister rust fungus in the western United States.

Cronartium ribicola, the causal agent of white pine blister rust, has been devastating to five-needled white pines in North America since its introduction nearly a century ago. However, dynamic and complex interactions occur among C. ribicola, five-needled white pines, and the environment. To examine potential evolutionary influences on genetic structure and diversity of C. ribicola in western United States, population genetic analyses of C. ribicola were conducted using amplified fragment length polymorphism (AFLP) molecular markers. The fungus was sampled at six sites. Collections for two of the six sites were from separate plantings of resistant-selected western white pine and sugar pine. Heterozygosity based on polymorphic loci among populations ranged from 0.28 to 0.40, with resistant-selected plantations at the extremes. Genetic differentiation was also highest between these two populations. Principal coordinates analysis and Bayesian assignment placed most isolates that are putative carriers of virulence to major-gene resistance into a discernable cluster, while other isolates showed no clustering by site or host species. These results indicate that C. ribicola in western North America is not genetically uniform, despite its presumed single site of introduction and relatively brief residence. Moreover, major-gene resistance appears to have imposed strong selection on the rust, resulting in reduced genetic diversity. In contrast, no evidence of selection was observed in C. ribicola from hosts that exhibit only multigenic resistance.

Synoptic climatology of the long-distance dispersal of white pine blister rust II. Combination of surface and upper-level conditions.

An invasive forest pathogen, Cronartium ribicola, white pine blister rust (WPBR), is believed to have arrived in the Sacramento Mountains of south-central New Mexico about 1970. Epidemiological and genetic evidence supports the hypothesis that introduction was the result of long-distance dispersal (LDD) by atmospheric transport from California. This study applies a method to identify the atmospheric conditions favorable for rust transport and infection. An upper level synoptic classification (ULSC) identifies patterns of upper-level flow favorable for the transport of rust spores from a source to a target. Transport data are coupled with data for surface conditions favorable for infection at a designated target. A resulting calendar lists likelihood classes for establishment by four-times-daily observations during a dispersal season from April through July in the years 1965 to 1974. The single most-favorable period for transport and infection at the New Mexico site was identified as 1-15 June 1969. Five additional sites in the western United States with susceptible white pine populations and known infestation status were then evaluated to verify the model. Only the infested sites exhibit an establishment likelihood of "high" or "very high." This suggests that the methodology correctly identifies locations with elevated establishment likelihood. Finally, likelihoods at nine additional points in the southwestern United States are determined and used to map regional patterns of transport, infection and establishment. The ULSC combined with appropriate surface meteorological data could be used to further investigate transport and infection, identify other areas at risk, assess the potential for gene flow of WPBR and evaluate long-distance dispersal of other pathogens.

Synoptic climatology of the long-distance dispersal of white pine blister rust. I. Development of an upper level synoptic classification.

This study developed a methodology to temporally classify large scale, upper level atmospheric conditions over North America, utilizing a newly-developed upper level synoptic classification (ULSC). Four meteorological variables: geopotential height, specific humidity, and u- and v-wind components, at the 500 hPa level over North America were obtained from the NCEP/NCAR Reanalysis Project dataset for the period 1965-1974. These data were subjected to principal components analysis to standardize and reduce the dataset, and then an average linkage clustering algorithm identified groups of observations with similar flow patterns. The procedure yielded 16 clusters. These flow patterns identified by the ULSC typify all patterns expected to be observed over the study area. Additionally, the resulting cluster calendar for the period 1965-1974 showed that the clusters are generally temporally continuous. Subsequent classification of additional observations through a z-score method produced acceptable results, indicating that additional observations may easily be incorporated into the ULSC calendar. The ULSC calendar of synoptic conditions can be used to identify situations that lead to periods of extreme weather, i.e., heat waves, flooding and droughts, and to explore long-distance dispersal of airborne particles and biota across North America.

Barrier to Gene Flow Between Eastern and Western Populations of Cronartium ribicola in North America.

ABSTRACT The population structure of Cronartium ribicola from eastern and western North America was studied to test the null hypothesis that populations are panmictic across the continent. Random amplified polymorphic DNA markers previously characterized in eastern populations were mostly fixed in western populations, yielding high levels of genetic differentiation between eastern and western populations (phi(st) = 0.55; theta = 0.36; P < 0.001). An unweighted pair-group method, arithmetic mean dendro-gram based on genetic distances separated the four eastern and four western populations into two distinct clusters along geographic lines. Similarly, a principal component analysis using marker frequency yielded one cluster of eastern populations and a second cluster of western populations. The population from New Mexico was clearly within the western cluster in both analyses, confirming the western origin of this recent introduction. This population was completely fixed (H(j) = 0.000; n = 45) at all loci suggesting a severe recent population bottleneck. Genetic distances were low among populations of western North America (0.00 to 0.02) and among eastern populations (0.00 to 0.02), indicating a very similar genetic composition. In contrast, genetic distances between eastern and western populations were large, and all were significantly different from 0 (0.07 to 0.19; P < 0.001). Indirect estimates of migration were high among western populations, including the number of migrants among pairs of populations (Nm > 1) between New Mexico and British Columbia populations, but were smaller than one migrant per generation between eastern and western populations. These results suggest the presence of a barrier to gene flow between C. ribicola populations from eastern and western North America.

Western Dwarf Mistletoe Parasitizing Colorado Blue Spruce and Norway Spruce in California.

Western dwarf mistletoe (Arceuthobium campylopodum Engelm.), a common parasite of ponderosa pine (Pinus ponderosa Dougl. ex Laws.) and Jeffrey pine (Pinus jeffreyi Grev. & Balf.), was found parasitizing planted Colorado blue spruce (Picea pungens Engelm.) and Norway spruce (Picea abies (L.) H. Karsten) in Upper Cuddy Valley, CA (Kern County, T. 9 N., R. 21 W., Sec. 25). One tree greater than 6 m in height of each spruce species was infected and both trees were within 12 m of a Jeffrey pine severely infected with western dwarf mistletoe. Five to 10 branches were infected on each tree and a few of these had abundant mistletoe shoot production, which allowed identification of the parasite. This is the first report of western dwarf mistletoe on Colorado blue spruce. Although this is the first report of natural infection of Norway spruce in California, this mistletoe/host combination has been reported by Weir from artificial inoculation (2) and collected by Russell in central Washington (1). We recommend that these spruce species not be planted within 15 m of pines infected with western dwarf mistletoe. Specimens of western dwarf mistletoe on Colorado blue spruce and Norway spruce were collected and deposited at the Deaver Herbarium, Northern Arizona University, Flagstaff. References: (1) F. G. Hawksworth and D. Wiens. 1996. Dwarf Mistletoes: Biology, Pathology, and Systematics. USDA Agric. Handb. 709. (2) J. R. Weir. Bot. Gaz. 56:1, 1918.