A First Generation Heterobasidion Hybrid Discovered in Larix lyalli in Montana

On September 25, 2010, a wood sample was collected from an entirely decayed root ball of an alpine larch (Larix lyallii Parl.), 10 cm in diameter at breast height, recently downed, but still green. No attempts were made to determine whether the decay progressed into the stem. The discovery occurred in a stand in the Bitterroot Mountains, south of Darby, Montana (elev. 2,530 m; 45.893528° N, 114.278322° W). Several adjacent alpine larches were either dead or displayed thin crowns, and an old Heterobasidion basidiocarp was found on the decayed root ball of a neighboring dead tree, suggesting the presence of a root disease pocket. The stand is mature and composed of alpine larch, whitebark pine (Pinus albicaulis Engelm.), and a few subalpine firs (Abies lasiocarpa (Hooker) Nuttall), but only larches were symptomatic. No stumps were visible, and the site is in a designated wilderness area characterized by minimal forest management. Wood chips displaying a white rot with bleached speckles were plated on 2% malt agar, and cultures displaying the typical Heterobasidion anamorph (Spiniger meineckellus) were visible after 7 days. DNA was extracted from two distinct cultures, and the sequences of three nuclear loci, namely the internal transcribed spacer, the elongation factor 1-alpha, and the glyceraldehyde 3-phosphate dehydrogenase, were analyzed. The sequence of the mitochondrial ATPase was also sequenced. All loci were amplified using the primers indicated in Linzer et al. (2). Sequences of all three nuclear loci (GenBank Accession Nos. KF811480 to 82) unequivocally indicated both isolates to be first generation hybrids between H. irregulare (Underw.) Garbel. & Otrosina and H. occidentale Otrosina & Garbel. Cumulatively, sequences were heterozygous at over 40 positions in all three loci, and for the presence of two indels (one in ITS, one in EF 1-alpha). Polymorphisms and indels indicated alleles from both species were present in these heterokaryotic (ploidy n+n) isolates. The mitochondrial ATPase (KF811483 to 84) indicated instead the cytoplasm belonged to H. occidentale, suggesting that species was the first to be established in the infected tree and was either dikaryotized by a basidiopsore of the other species, or subject to nuclear re-assortment through di-mon mating with a genotype of H. irregulare. This is the first report of a Heterobasidion sp. in L. lyalli, and it is the second report of a natural Heterobasidion hybrid in North America (1). This finding indicates Alpine larch may be a host for both Heterobasidion species, as described for pine stumps in California (1). Thus, this conifer may have provided a substrate for the hybridization and interspecific gene introgression documented to have occurred before stumps were generated in high frequency by modern forestry practices (2). References: (1) M. Garbelotto et al. Phytopathology 86:543, 1996. (2) R. Linzer et al. Mol. Phylogenet. Evol. 46:844, 2008.

Two new dothideomycetous endoconidial genera from declining larch

Two endoconidial, black meristematic fungi, Celosporium larixicolum gen. et sp. nov. (Dothideales) and Hispidoconidioma alpina gen. et sp. nov. (Capnodiales) are described from black subicula on twigs of declining larch ( Larix lyallii Parl) trees in Alberta, Canada. Conidioma morphology and phylogenetic analysis of LSU and ITS regions indicate that these taxa are both distinct from each other and from previously described endoconidial genera. Conidiomata of C. larixicolum consist of black cellular clumps (aggregated conidiogenous cells) that are either naked or enveloped by scant to dense mycelium that sometimes organizes into a cupulate peridium. Endoconidia are 1–3 celled, hyaline when released but become pigmented as they age, and very variable in size and shape, e.g., globose, pear-shaped, osteoid, or discoid with an irregular flange. In H. alpina, colonies are three-layered, consisting of a central pseudoparenchymatous layer sandwiched between an upper and a basal hyphal layers, and conidiogenesis occurs in sporadic areas of the central layer. Endoconidia are unicellular, hyaline, and subglobose to ellipsoid. The strong phylogenetic affinities between these newly described taxa and slow-growing, melanized fungi isolated from rocks suggest individual black meristematic fungus lineages may have broad habitat ranges.

Reconstructed summer temperature in the northern Rocky Mountains wilderness, USA

Ring widths from whitebark pine (Pinus albicaulisEnglem.) and subalpine larch (Larix lyalliiParl.) collected at three high-elevation sites were used to develop tree-growth chronologies to reconstruct summer temperature anomalies. A step-wise multiple regression procedure was used to screen potential predictor variables to generate a transfer function capable of skillfully reconstructing summer temperature. The resulting regression model explained approximately 38% of the adjusted variance in the instrumental temperature record. The fidelity of the reconstruction was verified using product mean and sign tests, both of which suggested significant predictive power in the reconstructions (p<0.05). Reduction of error (RE) and coefficient of efficiency (CE) measures were both positive, indicating the reconstruction contained useful climate information. Cool periods often coincided with reduced solar activity and/or periods of increased volcanic activity. Differences between this reconstruction and others encompassing a broader geographic scale highlight the importance of developing local reconstructions of climate variability, particularly when used in conjunction with ecological data sets that describe the occurrence of fires or insect epidemics. Mixed and divergent climate-response relationships were evident in the whitebark pine chronologies and suggest subalpine larch may be a more useful species than whitebark pine to target for the development of temperature reconstructions in this region.

Cone entomofauna of whitebark pine and alpine larch (Pinaceae): potential impact of Leptoglossus occidentalis (Hemiptera: Coreidae) and a new record of Strobilomyia macalpinei (Diptera: Anthomyiidae)

Laboratory and field feeding tests with Leptoglossus occidentalis Heidemann demonstrated that both immature and mature seed bugs can use cones and foliage of whitebark pine, Pinus albicaulis Engelmann, as a food source for 1- to 2-week periods. Damage to unprotected whitebark pine cones by seed bugs ranged from 0.3 to 2.1% of seeds per cone. Total insect damage ranged from 0.4 to 7.1% of seeds per cone. A seed chalcid, Megastigmus Dalman. sp. (Hymenoptera: Torymidae), was documented for the first time on whitebark pine and was found in 4.7% of examined seeds at one site. The larch cone fly, Strobilomyia macalpinei Michelsen, was reared from cones of alpine larch, Larix lyallii Parl., from the Bitterroot Range of Montana. This is the first record of this species in the United States and the first since its description in 1988. Ninety-four percent of a sample of alpine larch cones were damaged by cone fly larvae and 64% contained larvae or puparia.

Reconstruction of Annual Temperature (1590–1979) for Longmire, Washington, Derived from Tree Rings

Annual growth records from trees at timberline in the Cascade Range of Washington are correlated with variations in temperature and snow depth and used to reconstruct climatic variation in the past. Response surfaces indicate that growth of mountain hemlock (Tsuga mertensiana) and subalpine larch (Larix lyallii) is positively correlated with summer (July to September) temperature and negatively correlated with spring (March) snow depth when snow depth is at or below average. During years of above average snow depth, temperature has little effect on mountain hemlock but has a negative effect on growth in subalpine larch. These interactions make it difficult to reconstruct these climatic variables separately using standard methods. Mean annual temperature values, which combine information on both summer temperature and spring snow depth, were estimated from a regression model that reconstructs past temperature at Longmire, Washington, as a function of larch and hemlock tree-ring chronologies. The reconstruction of mean annual temperature shows temperatures between 1590 and 1900 to be approximately 1°C lower than those of the 20th century. Only during a short period from 1650 to 1690 did temperatures approach 20th-century values.