Geral I. McDonald

Effect of white pine blister rust (Cronartium ribicola) and rust-resistance breeding on genetic variation in western white pine (Pinus monticola)

Abstract.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 Dices 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.

Use of flow cytometry, fluorescence microscopy, and PCR- based techniques to assess intraspecific and interspecific matings of Armillaria species

For assessments of intraspecific mating using flow cytometry and fluorescence microscopy, two compatible basidiospore-derived isolates were selected from each of four parental basidiomata of North American Biological Species (NABS) X. The nuclear status in NABS X varied with basidiospore-derived isolates. Nuclei within basidiospore-derived isolates existed as haploids, diploids (doubled haploids), or a mixture of haploids and diploids (doubled haploids). Depending on the nuclear status of the basidiospore-derived lines of NABS X, intraspecifically mated cultures can exist as diploids or tetraploids, and possibly triploids or aneuploids under in vitro conditions. Based on previous in vitro mating studies, seven basidiospore isolates were specifically selected to assess rare, interspecific mating among Armillaria cepistipes, A. sinapina, NABS X, and NABS XI. Cultures from basidiospore-derived isolates were paired to produce four interspecifically paired cultures, and matings were assessed using flow cytometry and restriction fragment length polymorphism (RFLP) analyses. Based on flow cytometric analysis, the A. cepistipes isolate exhibited compatibility with a NABS X isolate, and the A. sinapina isolate exhibited compatibility with a NABS X isolate, and the A. sinapina isolates were individually compatible with isolates of NABS X and NABS XI. Mean fluorescence intensities of A. cepistipes‹NABS X, A. sinapina‹NABS X, and A. sinapina‹NABS XI mated cultures revealed a triploid or tetraploid nuclear status compared to the haploid or diploid (doubled haploid) nuclear status of initial basidiospore-derived isolates. Polymerase chain reaction (PCR) and RFLP of the intergenic spacer (IGS) region generated banding patterns for basidiospore-derived isolates and mated cultures. Four species-specific RFLP banding patterns were observed in basidiospore-derived isolates of A. cepistipes, A. sinapina, NABS X, and NABS XI. PCR-RFLP analysis showed combined banding patterns from mated cultures. Flow cytometry and PCR-RFLP analysis are eective tools to assess matings of Armillaria species.

Genetic diversity and structure of western white pine (Pinus monticola) in North America: a baseline study for conservation, restoration, and addressing impacts of climate change

Western white pine (Pinus monticola) is an economically and ecologically important species in western North America that has declined in prominence over the past several decades, mainly due to the introduction of Cronartium ribicola (cause of white pine blister rust) and reduced opportunities for regeneration. Amplified fragment length polymorphism (AFLP) markers were used to assess the genetic diversity and structure among populations at 15 sites (e.g., provenances) across the native range of western white pine. The level of genetic diversity was different among 15 populations tested using 66 polymorphic AFLP loci. Nei’s gene diversity (HE) at the population level ranged from 0.187 to 0.316. Genetic differentiation (GST) indicated that 20.1% of detected genetic variation was explained by differences among populations. In general, populations below 45oN latitude exhibited a higher level of genetic diversity than higher latitude populations. Genetic distance analysis revealed two major clades between northern and southern populations, but other well-supported relationships are also apparent within each of the two clades. The complex relationships among populations are likely derived from multiple factors including migration, adaptation, and multiple glacial refugia, especially in higher latitudes. Genetic diversity and structure revealed by this study will aid recognition and selection of western white pine populations for species management and conservation programs, especially in consideration of current and future climate changes.

Effects of nursery environment on needle morphology of Pinus monticola Dougl. and implications for tree improvement programs.

Statistically significant differences were found in 14 needle traits of western white pine (Pinus monticola Dougl.) seedlings grown from the same seed orchard source in the three nurseries in northern Idaho. Traits with significant variation included needle length and width, number of stomatal rows, number of stomata per row, total stomata per needle, adaxial surface area, stomatal density, major axes of stomata, stomatal shape, stomatal area, stomatal occlusion, epistomatal wax degradation, weight of wax per dry weight of needle, and the contact angles of water droplets placed on adaxial needle surfaces. Wax crystallites on needle surfaces were hollow and tubular and the amount of surface wax appeared to be associated with surface wettability. Our results may have important implications for tree improvement programs that require successful inoculation of nursery-grown seedlings with spores of Cronartium ribicola J. C. Fisch. ex Rabenh. to reliably screen white pines for resistance to blister rust.