Can microscale meteorological conditions predict the impact of white pine Blister Rust in Colorado and Wyoming

White pine Blister Rust occurs when there are compatible interactions between susceptible hosts (white pines and Ribes spp.), inoculum (Cronartium ribicola spores), and local weather conditions during infection. The five spore stages of the white pine Blister Rust (WPBR) fungus have specific temperature and moisture conditions necessary for production, germination, and dissemination of spores. Local meteorological conditions may be important factors in infection success, infection periodicity and disease intensification over time.

White pine Blister Rust in the interior Mountain West

White pine Blister Rust is an exotic, invasive disease of white, stone, and foxtail pines (also referred to as white pines or five-needle pines) in the genus Pinus and subgenus Strobus (Price and others 1998). Cronartium ribicola, the fungus that causes WPBR, requires an alternate host – currants and gooseberries in the genus Ribes and species of Pedicularis and Castilleja (McDonald and others 2006, Zambino and others 2007) – to complete its life cycle. White pine Blister Rust was discovered in western North America in 1921. It is thought that the disease was accidentally introduced on infected eastern white pine (Pinus strobus) nursery stock shipped to Vancouver, BC from Europe in the early 1900s but the specific details are unclear. Since then, the disease has spread throughout the distributions of most western white pines. Although all of the North American white pine species are susceptible to white pine Blister Rust (Bingham 1972, Hoff and others 1980), it was once thought that the remote, dry habitats occupied by the noncommercial, high elevation white pines would not support Rust establishment. Unfortunately, white pine Blister Rust can now be found in many of these areas.

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). Neith…

whitebark pine prevalence and ecological function in treeline communities of the greater yellowstone ecosystem u s a potential disruption by white pine Blister Rust

In the northern Rocky Mountains of the U.S. and Canada, whitebark pine (Pinus albicaulis Engelm.) is a functionally important species in treeline communities. The introduced fungal pathogen Cronartium ribicola, which causes white pine Blister Rust, has led to extensive whitebark pine mortality nearly rangewide. We examined four treeline communities within the Greater Yellowstone Ecosystem (GYE) to assess structure and composition, whitebark pine prevalence and functional role, differences in growing season mesoclimate among study areas, and Blister Rust infection incidence. We found that (1) whitebark pine frequently serves as the majority overall, solitary, and leeward tree island conifer; (2) the prevalence of different tree species in the windward position in tree islands, and thus their potential as tree island initiators, may be predicted from their relative abundance as solitary trees; and (3) white pine Blister Rust infection incidence ranged from 0.6% to 18.0% across study areas. White pine Blister Rust poses a threat to treeline development and structure and the provision of ecosystem services in the GYE. Increasing Blister Rust resistance in nearby subalpine whitebark pine communities through seedling planting or direct seeding projects should eventually result in higher levels of Blister Rust resistance in whitebark pine in treeline communities.

topographic influences on the distribution of white pine Blister Rust in pinus albicaulis treeline communities

The exotic disease white pine Blister Rust (caused by Cronartium ribicola) damages and kills whitebark pine (Pinus albicaulis), even in the extreme environments of alpine treeline communities. We surveyed P. albicaulis trees and tree islands for Blister Rust in 2 distinct alpine treeline communities in Montana, USA, and examined meso- and microtopographic factors potentially related to the climatic requirements for Blister Rust infection. For each of 60 sampling plots, we created high-resolution digital elevation models, derived microtopography variables, and compared these and distance to water feature variables with Blister Rust occurrence and intensity (number of cankers per infected tree) for every sampled P. albicaulis tree. Infection rates were 19% (of 328 sampled trees) and 24% (of 585 sampled trees) at the 2 sites. Tree island P. albicaulis had higher infection percentages than solitary trees. Using Bayesian analysis and a zero-inflated Poisson regression model, we determined that solar radiation and moisture-related variables correlated with both presence and number of Blister Rust cankers on P. albicaulis. Site factors that influence moisture, such as local topography, hydrology, and climate, differed between the 2 treeline study areas, which may account for the model variability.

Blister Rust and western forest biodiversity ecology values and outlook for white pines

Summary

Eight white pine species are widely distributed among the forests of western Canada and the United States. The different forest communities with these species contribute biodiversity to the western landscape. The trees themselves provide various ecosystem services, including wildlife habitat and watershed protection. White pine communities range in elevation from lower to upper treeline, in successional stage from seral to climax, and in stand type from krummholz to closed-canopy forest. Many white pine species are moderately to strongly fire-dependent for regeneration; several species are extreme stress tolerators and persistent on harsh sites. Among the white pines are the oldest-living trees, the world’s largest pines, species dependent on birds for seed dispersal, species important for grizzly bear habitat and species of high commercial timber value. The principal threats to white pine populations are Blister Rust (Cronartium ribicola, pathogen), fire suppression, succession, mountain pine beetle and climate change. Severe population declines in several white pine species are attributed to losses caused by these factors acting either alone or together, and sometimes in concert with logging and other land-use changes. The importance and particular interactions of these threats vary by region and species. For example, many northern and western populations of whitebark pine are seriously declining from a combination of mountain pine beetle outbreaks and severe Blister Rust infestations. As whitebark pines provide many keystone services on high-elevation sites, their loss would impact forest composition and structure, succession, biodiversity, and ecosystem services. Although there are serious challenges to science-based management and conservation (especially in remote American wilderness areas), prompt and effective intervention promoting regeneration of Blister Rust-resistant white pines could mitigate these severe impacts.

Non-Ribes alternate hosts of white pine Blister Rust: What this discovery means to whitebark pine

From early to present-day outbreaks, white pine Blister Rust caused by the fungus Cronartium ribicola, in combination with mountain pine beetle outbreaks and fire exclusion has caused ecosystem-wide effects for all five-needled pines (McDonald and Hoff 2001). To be successful, efforts to restore whitebark pine will require sound management decisions that incorporate an understanding of many interacting factors, including the biology and life cycle of the fungus, whether it may adapt and change its behavior when exposed to different environments and hosts, and mechanisms and predicted frequencies of resistance in current and regenerating stands and populations of its hosts. Despite the long history of white pine Blister Rust on whitebark pine, significant gaps in our knowledge of the pathogen, the disease, and resistance are increasingly apparent. Our recent discovery of non-Ribes alternate hosts for the white pine Blister Rust fungus is an illustration of this point.

effect of white pine Blister Rust cronartium ribicola and Rust resistance breeding on genetic variation in western white pine pinus monticola

Western white pine (Pinus monticola) is an economically and ecologically important species from western North America that has declined over the past several decades mainly due to the introduction of Blister Rust (Cronartium ribicola) and reduced opportunities for regeneration. Amplified fragment length polymorphism (AFLP) was used to assess the genetic variation in northern Idaho populations of western white pine (including Rust-resistant breeding stock) in relation to Blister Rust. A total of 176 individuals from four populations was analyzed using 163 AFLP loci. Within populations, an average 31.3% of the loci were polymorphic (P), and expected heterozygosity (He) was 0.123. Genetic differentiation values (Gst) showed that 9.4% of detected genetic variation was explained by differences among populations. The comparison between the Rust-resistant breeding stock and a corresponding sample derived from multiple natural populations produced similar values of P (35% vs. 34.4%) and He (0.134 vs. 0.131). No apparent signs of a genetic bottleneck caused by Rust-resistance breeding were found. However, a comparison of two natural populations from local geographic areas showed that the population with low pressure from Blister Rust had higher polymorphism and heterozygosity than the population that had experienced high mortality due to Blister Rust: P (30.7% vs. 25.1%) and He (0.125 vs. 0.100), respectively. In addition, the population from low Blister–Rust pressure had twice as many unique alleles as the Blister Rust-selected population. The genetic distance and Dice’s similarity coefficients among the four populations indicated that the local population that survived high Blister–Rust pressure was genetically similar to the Rust-resistant breeding stock.

Differences in needle morphology between Blister Rust resistant and susceptible western white pine stocks

Needle traits were evaluated on three groups of western white pine (Pinus monticola Dougl.) seedlings: four open-pollinated families that ranked high for the “reduced needle lesion frequency” type of resistance to Blister Rust; four Blister Rust susceptible families; and two bulk lots from a seed orchard selected for Blister Rust resistance. No statistically significant differences were found for most traits in pairwise comparisons among the three groups. However, needles of susceptible families had significantly wider and larger stomata (greater area) than did those of resistant families and seed orchard lots; their stomata were also rounder (smaller ratio of stomatal length to width) than those of the seed orchard lots. Needles of the resistant stocks were significantly shorter than those from seed orchard bulks. Contact angles of water droplets on adaxial needle surfaces were also significantly larger on resistant families compared with the other genetic stocks. Results suggest the possibility of some threshold stomatal size and (or) critical stomatal shape related to infection by the Blister Rust fungus, Cronartium ribicola J.C. Fisch. ex Rabenh., and possible differences among the groups in wax chemistry and (or) surface textures, both of which may alter behavior of Blister Rust germ tubes and (or) be altered by Blister Rust infection.