For over a century, white pine blister rust (Cronartium ribicola) has linked white pines (Strobus) with currants and gooseberries (Ribes) in a complex and serious disease epidemic in Asia, Europe, and North America. Because of ongoing changes in climate, societal demands for forests and their amenities, and scientific advances in genetics and proteomics, our current understanding and management of the white pine blister rust pathosystem has become outdated. Here, we present a review and synthesis of international scope on the biology and management of blister rust, white pines, Ribes, and other hosts. In this article, we provide a geographical and historical background, describe the taxonomy and life cycle of the rust, discuss pathology and ecology, and introduce a series of invited papers. These review articles summarize the literature on white pines, Ribes, and blister rust with respect to their status, threats, and management through genetics and silviculture. Although the principal focus is on North America, the different epidemics in Europe and Asia are also described. In the final article, we discuss several of the key observations and conclusions from the preceding review articles and identify prudent actions for research and management of white pine blister rust.
The volatile oils of the leaves and twigs of alpine fir, and western and eastern Canadian balsam fir were analyzed by gas–liquid chromatography. Many qualitative similarities were found and the within-tree and tree-to-tree variation of the quantitative terpene composition of the leaf oil was sufficiently small to permit a chemosystematic study. Abies lasiocarpa and A. balsamea may be differentiated by the relative amounts of β-pinene, 3-carene, β-phellandrene, trans-ocimene, piperitone, methyl thymol, and thymol. Consistent quantitative differences were also found between eastern and western A. balsamea, and the populations in the Lesser Slave Lake and Battle Lake regions of central Alberta gave intermediate terpene data, which suggests introgression between A. lasiocarpa and western A. balsamea. Thus a cline between A. lasiocarpa and A. balsamea, with western balsam fir populations as bridge, may have existed after the last glaciation. The alpine fir populations of southern Alberta, and eastern and central British Columbia gave uniform terpene data, but five trees sampled on Green Mountain, Vancouver Island, gave significantly different terpene data. These results were substantiated by morphological characters as well as twig oil analysis, but the latter two methods gave less consistent data than leaf oil analysis.
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.
Blister rust (Cronartium ribicola) entered Europe about 300 years after eastern white pine (Pinus strobus) was first planted in Europe. North America imported millions of infected seedlings after blister rust was firmly established throughout Europe. Blister rust probably entered into western North America on multiple occasions and spread throughout British Columbia (BC) by about 1930. Two large saw mills solely cutting western white pine (P. monticola) started in the 1920s with the main production for matches. Blister rust surveys in the 1940s painted a poor picture for the future of western white pine in BC, so it was discriminated against in forest management plans. Harvest volumes declined and the 2 mills ceased production about 1960. Selection of resistant clones from mature parents occurred between 1948 and 1960, but when it was evident that mature tree resistance was not likely to be in their seedlings the program was terminated. A program based on screening seedlings was started in 1983. The selected seedlings are hypothesized to possess age-related resistance that is being expressed at an early age. These and the better parents are incorporated into orchards. Key words: Cronartium, white pine, surveys, match blocks, rust resistance, PR proteins
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