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Summary: Dwarf mistletoes (Arceuthobium spp.) are a group of obligate, hemiparasitic plants that infect numerous species in the Pinaceae in North America. Wildland fire is considered to be the primary natural agent influencing the population and distribution of dwarf mistletoes across landscapes. Based on this understanding, prescribed fire has been suggested as a potential method for dwarf mistletoe sanitation and control; however, experimental work has primarily focused on prescribed surface fire. In this study, we report long‐term impacts of three experimental crown fires on dwarf mistletoe severity in infested lodgepole pine stands in Colorado 33 years post‐fire. The three fires achieved tree mortality rates ranging from 20% to 100%. Our results suggested a significant negative relationship between the amount of fire‐caused tree mortality and future dwarf mistletoe severity. These findings supported the presumed natural role of fire in altering dwarf mistletoe populations, which perhaps exhibits a linear relationship between fire‐caused host tree mortality and future dwarf mistletoe severity. [ABSTRACT FROM AUTHOR]

Conifer trees resist pest and pathogen attacks by complex defense responses involving different classes of defense compounds. However, it is unknown whether prior infection by biotrophic pathogens can lead to subsequent resistance to necrotrophic pathogens in conifers. We used the infection of jack pine, Pinus banksiana, by a common biotrophic pathogen dwarf mistletoe, Arceuthobium americanum, to investigate induced resistance to a necrotrophic fungus, Grosmannia clavigera, associated with the mountain pine beetle, Dendroctonus ponderosae. Dwarf mistletoe infection had a non-linear, systemic effect on monoterpene production, with increasing concentrations at moderate infection levels and decreasing concentrations at high infection levels. Inoculation with G. clavigera resulted in 33 times higher monoterpene concentrations and half the level of phenolics in the necrotic lesions compared to uninoculated control trees. Monoterpene production following dwarf mistletoe infection seemed to result in systemic induced resistance, as trees with moderate disease severity were most resistant to G. clavigera, as evident from shorter lesion lengths . Furthermore, trees with moderate disease severity had the highest systemic but lowest local induction of α-pinene after G. clavigera inoculation, suggesting a possible tradeoff between systemically- and locally-induced defenses. The opposing effects to inoculation by G. clavigera on monoterpene and phenolic levels may indicate the potential for biosynthetic tradeoffs by the tree between these two major defense classes. Our results demonstrate that interactions between a biotrophic parasitic plant and a necrotrophic fungus may impact mountain pine beetle establishment in novel jack pine forests through systemic effects mediated by the coordination of jack pine defense chemicals. [ABSTRACT FROM AUTHOR]

Arceuthobium americanum Nutt. ex Engelm. (lodgepole pine dwarf mistletoe) is a dioecious plant parasitizing conifers in North America. Here, we documented changes in the 'taxonomic richness' of culturable endophytic fungi in male and female A. americanum over the growing season. Endophytic fungi were isolated from vegetative stems of surface-sterilized aerial shoots from male and female A. americanum collected weekly from April to September. Isolated fungi were characterized macroscopically, generating a database of 48 morphologically unique forms that likely represented individual taxa. A random sample of endophytic fungi was sequenced to determine identity based on ITS rDNA. Richness increased throughout the growing season similarly in the stems of both sexes, suggesting that increased developmental age or time in the environment facilitates an increase in endophyte richness: male and female endophyte communities were 91% similar based on Sorensen's coefficient. Sequenced endophytes came from many diverse taxa, including Serpula, Alternaria, and Tremella, which may function as mutualistic symbionts within the mistletoe. An increase in fungal richness throughout the growing season has been observed in all flowering plants examined to date, although our observation is the first for the genus and for parasitic plants in general, and has also contributed to knowledge of fungal diversity in dioecious plants. [ABSTRACT FROM AUTHOR]

Arceuthobium americanum Nutt. ex Engelm., the lodgepole pine dwarf mistletoe, is a dioecious parasitic flowering plant infecting lodgepole pine ( Pinus contorta subsp. latifolia (Engelm.) Critchfield) in the Pacific Northwest, compromising timber value by stunting the host's growth. The plant disperses its seeds by explosive discharge, and thus understanding its reproduction is an integral step toward managing its spread. The life cycle of Arceuthobium americanum occurs over five to six years, and the fruit matures over two consecutive growing seasons, dispersing in the second. Using low-vacuum environmental scanning electron microscopy (eSEM), we examined branching architecture as well as the morphology and anatomy of fruits during their second year of development up to explosive discharge. We found that branching patterns shifted from opposite-decussate to verticillate after several years' growth. In addition, the perianth parts (sepals), style, and stigma persisted through the season, and the fruit's abscission zone developed slightly distal to the end of the pedicel. Stomata, found only on the sepals, were located in crypts surrounded by two subsidiary cells, and stomatal density significantly decreased during development. The decline in stomatal density along with the thick pericarp cuticle may function in retaining water inside the fruit to facilitate discharge and (or) provide a heating mechanism through reduced transpiration. [ABSTRACT FROM AUTHOR]

Dwarf mistletoes (DM), genus Arceuthobium, are dioecious parasitic flowering plants having prolonged life cycles lasting six years, culminating with explosive discharge of the single seed from the fruit. Arceuthobium americanum Nutt. ex Engelm., the lodgepole pine dwarf mistletoe, infects lodgepole pine ( Pinus contorta subsp. latifolia (Engelm.) Critchfield) in western North America, compromising the forest economy. Highly reduced flowers appear no later than two years following shoot development, with female flowers appearing and persisting for over two years. Development of the pistillate plant, including initiation of floral growth, has not been fully explored. Here, we used environmental scanning electron microscopy to demark phenological waypoints throughout the pistillate plant's development. As successive crops of female flowers emerged every year, up to three generations of flowers/fruit could be found on a single shoot in late summer; we used these three generations to delineate specific developmental stages. Vegetative shoots could initiate growth at any time within the growing season, could assume a terminal position, could also adopt sympodial branching, but were never whorled or adventitious. Floral branches, however, could initiate adventitiously from older nodes in a whorled pattern, and could house flowers/fruits of any generation. Vegetative and floral units were structurally homogeneous, suggesting shared developmental pathways. [ABSTRACT FROM AUTHOR]

Parasitic plants are capable of causing substantial alterations to plant communities through impacts on individual host plants. Lodgepole pine dwarf mistletoe is an important parasite in forests of the western USA that causes reductions to productivity and is thought to alter wildland fuel complexes. These impacts are hypothesized to vary with infestation severity. To test this, we used a linear mixed modeling approach to evaluate the relationship between dwarf mistletoe infestation severity and parameters representing stand structure and surface and canopy fuels in infested lodgepole pine stands in central Colorado. Infestation severity was negatively related to live basal area, average tree size, canopy base height, canopy fuel load, and canopy bulk density, and was positively related to the loading of woody surfaces fuels greater than 0.64 cm in diameter. No relationship was detected between infestation severity and live tree density, or live crown ratio. These results confirm the long-held assumption that dwarf mistletoe increases surface fuel loading in lodgepole pine communities, but also suggest that infested stands have reduced amounts of available canopy fuel. These findings have implications for potential fire behavior and highlight the importance of dwarf mistletoe in predicting the spatial and temporal dynamics of wildland fuels. [ABSTRACT FROM AUTHOR]

Plant pathogens can have cascading consequences on insect herbivores, though whether they alter competition among resource-sharing insect herbivores is unknown. We experimentally tested whether the infection of a plant pathogen, the parasitic plant dwarf mistletoe ( Arceuthobium americanum), on jack pine ( Pinus banksiana) altered the competitive interactions among two groups of beetles sharing the same resources: wood-boring beetles (Coleoptera: Cerambycidae) and the invasive mountain pine beetle ( Dendroctonus ponderosae) (Coleoptera: Curculionidae). We were particularly interested in identifying potential mechanisms governing the direction of interactions (from competition to facilitation) between the two beetle groups. At the lowest and highest disease severity, wood-boring beetles increased their consumption rate relative to feeding levels at moderate severity. The performance (brood production and feeding) of mountain pine beetle was negatively associated with wood-boring beetle feeding and disease severity when they were reared separately. However, when both wood-boring beetles and high severity of plant pathogen infection occurred together, mountain pine beetle escaped from competition and improved its performance (increased brood production and feeding). Species-specific responses to changes in tree defense compounds and quality of resources (available phloem) were likely mechanisms driving this change of interactions between the two beetle groups. This is the first study demonstrating that a parasitic plant can be an important force in mediating competition among resource-sharing subcortical insect herbivores. [ABSTRACT FROM AUTHOR]

Dwarf mistletoes, genus Arceuthobium (Santalaceae), are parasitic angiosperms that spread their seeds by an explosive process. As gentle heating triggers discharge in the lab, we wondered if thermogenesis (endogenous heat production) is associated with dispersal. Thermogenesis occurs in many plants and is enabled by mitochondrial alternative oxidase (AOX) activity. The purpose of this study was to probe Arceuthobium americanum fruit (including seed tissues) collected over a 10-week period with an anti-AOX antibody/gold-labeled secondary antibody to determine if AOX could be localized in situ, and if so, quantitatively assess whether label distribution changed during development; immunochemical results were evaluated with Western blotting. No label could be detected in the mitochondria of any fruit or seed tissue, but was observed in fruit exocarp plastids of samples collected in the last 2 weeks of study; plastids collected in week 10 had significantly more label than week 9 ( p = 0.002). Western blotting of whole fruit and mitochondrial proteins revealed a signal at 30-36 kD, suggestive of AOX, while blots of whole fruit (but not mitochondrial fraction) proteins showed a second band at 40-45 kD, in agreement with plastid terminal oxidases (PTOXs). AOX enzymes are likely present in the A. americanum fruit, even though they were not labeled in mitochondria. The results strongly indicate that the anti-AOX antibody was labeling PTOX in plastids, probably at a C-terminal region conserved in both enzymes. PTOX in plastids may be involved in fruit ripening, although a role for PTOX in thermogenesis cannot be eliminated. [ABSTRACT FROM AUTHOR]

* Premise of the study: Endophytic fungi likely occur in all plants, yet little is known about those of parasitic plants, despite their potential to influence parasite success. Arceuthobium americanum is a parasitic angiosperm that greatly compromises the North American timber industry. We hypothesized that (1) A. americanum hosts fungal endophytes, and (2) these endophytes help A. americanum resist infection by fungal pathogens. * Methods: Healthy A. americanum stem and fruit tissues were differentially stained for cellulose and chitin and visualized using fluorescence microscopy. Stem sections (sterilized vs. unsterilized) and seeds were incubated on agar plates to cultivate fungi, both to extract DNA for ITS rDNA sequencing and to observe interactions with native fungi from unsterilized specimens. * Key results: Aside from xylem vessel elements, fungal structures were observed in all tissues, including those of the embryo. The ITS sequences of fungi cultured from internal tissues closely matched those of the known endophytes Phoma, Sydowia, and Phacidiopycnis, while those of surface organisms closely matched Cladosporium spp. Cultured fungi from internal tissues (putative endophytes) inhibited the growth of the surface organisms without affecting the other endophytes. * Conclusion: Fungal communities are established in A. americanum stems as well as in fruits and seeds, suggesting vertical transmission. These internally derived fungi act antagonistically toward fungi with pathogenic tendencies. As such, native mistletoe endophytes might protect A. americanum against fungal pathogens in nature. In the future, manipulation of endophytes might be a component of mistletoe control programs. [ABSTRACT FROM AUTHOR]

Infection of the endophytic system of Arceuthobium americanum parasitizing Pinus contorta var. latifolia by the fungus Colletotrichum gloeosporioides was assessed on naturally infected and inoculated localized dwarf mistletoe plants. Two different techniques were utilized to attempt to inoculate C. gloeosporioides into the endophytic system: the fungus was applied as Stabileze formulated product onto cut A. americanum shoots and as a mycelial plug to wounded A. americanum infected host branches. The fungus was cultured from infected shoots and the basal cup region of naturally infected A. americanum, but not pine tissues that included the endophytic system. Following inoculation of cut shoots, the shoots were abscised from the dwarf mistletoe plant, and the fungus was not isolated 1 year after inoculation. The fungus was recovered from the wounded region of infections that were inoculated with a mycelial plug, but not outside of the wounded area. Hyphae with morphology that matched that of C. gloeosporioides were observed microscopically in the shoots and basal cup region of naturally infected A. americanum, but not in the samples from the inoculated treatments. Thus, we were unable to confirm that C. gloeosporioides infected the endophytic system of A. americanum parasitizing P. contorta var. latifolia, although xylem continuity between the aerial and endophytic systems was observed. [ABSTRACT FROM AUTHOR]

In North America, the most widespread and speciose mistletoe is M. Bieb. (dwarf mistletoes, Viscaceae), which is a dioecious parasite of conifers. Little is known about its sex determination system, and sex chromosomes have not been identified. A genetic marker for early gender discrimination in Arceuthobium would be useful in the study of sex ratios and sex determination. Here, random amplified polymorphic DNA analysis via the polymerase chain reaction (PCR) was used to investigate genetic differences between genders in Nutt. ex Engelm. collected near Kamloops, British Columbia and Bélair, Manitoba. A total of 196 10-mer primers were selected for analysis of DNA from isolated male and female A. americanum somatic tissue. A ∼900 bp female-specific DNA fragment was generated with primer OPB-18 (5′-CCACAGCAGT-3′). The fragment was cloned and sequenced. Using GenBank and the basic local alignment search tool alignment software, it was determined that the first ∼300 bp of this DNA sequence shared a high degree of similarity to transposable elements (76%) and a Y-chromosome (male) fragment (75%) in Poir. Sequence-characterized amplified region primers were then designed. This study has generated an efficient molecular tool to differentiate male and female A. americanum while also providing evidence indicating that A. americanum may have homomorphic, possibly protoheteromorphic, sex chromosomes. [ABSTRACT FROM AUTHOR]

The lodgepole pine dwarf mistletoe, Arceuthobium americanum Nutt. ex Engelm., is a parasitic angiosperm that infects conifers in western Canadian forests. A striking feature of the Arceuthobium life cycle is explosive seed dispersal, triggered by hydrostatic build-up within the fruit, localized in a tissue called “viscin.” Viscin is composed of two cell types: “viscin cells” that accrue pressure in their hydrated mucilage, and “vesicular cells” with a previously undetermined function. The objective of this work was to investigate the development and composition of vesicular cells using microscopy, cytochemistry, and gas chromatography – mass spectroscopy. We found that vesicular cells are initiated from mesocarp cells lining the viscin cells. As development of the seed progresses, vesicular cells form a single layer, enlarge, and become isodiametric. Later, the cells make up all of the remaining 3–4 outer mesocarp layers. Concomitant with enlargement, intracellular triacylglycerides (TAGs) largely composed of 16-carbon and 18-carbon fatty acids, accumulate. Immediately prior to discharge, vesicular cell boundaries become indistinct, and the cell contents become confluent, creating a lipid mass between the viscin cells and the exocarp. Vesicular cells and their resulting lipid mass likely function in discharge by acting as a hydrophobic barrier to water loss and (or) as a repellant, resistant layer. [ABSTRACT FROM AUTHOR]

Arceuthobium americanum Nuttal ex Engelmann in Gray (lodgepole pine dwarf mistletoe) causes significant losses to the timber industry. The fungus Caliciopsis arceuthobii (Peck) Barr shows high specificity to Arceuthobium spp., and therefore infection of A. americanum was monitored for 4 years to determine the effect of this fungus on fruit production. The contribution of stand-level and locally produced inoculum in the infection process was also studied to better understand the epidemiology of the pathogen. Over the period of the study, C. arceuthobii caused an average annual fruit reduction of 58%. When the contribution of local and stand-level inoculum was modelled, the results suggested that on A. americanum infections with ≥ 4 ascospore-producing immature fruit, more than half of the new C. arceuthobii infections on the same plant are derived from locally produced ascospores. The effect of the fungus on the host suggests that it has potential as a biological control agent for A. americanum, and further studies are needed to attempt to induce inoculum production in culture. L'Arceuthobium americanum Nuttal ex Engelmann in Gray (faux-gui du pin lodgepole) cause des pertes significatives à l'industrie forestière. [ABSTRACT FROM AUTHOR]

The lodgepole pine dwarf mistletoe, Arceuthobium americanum Nutt. ex Engelm., is a dioecious angiosperm that parasitizes conifers in western Canadian forests, causing significant yearly timber loss. A striking consequence of dwarf mistletoe infection is a marked reduction in the size of the needles located distal to the infection. The purpose of this work was to use microscopy, cytochemistry, and biochemical analysis to determine whether this reduction was associated with changes in needle anatomy and (or) starch content. Furthermore, we wanted to investigate whether these potential changes were affected by the gender of the infecting dwarf mistletoe plant. We developed a ratio (R) that evaluated the position of the two vascular bundles relative to the size of the needle, and found that bundles from male-infected trees were positioned significantly closer together than in needles from female-infected or uninfected trees (p < 0.05). Using the periodic acid – Schiff’s (PAS) reaction for cytochemical identification of starch in situ, we determined that needles from uninfected trees had abundant starch grains compared with needles from infected trees; colourimetric analysis for total starch content corroborated our PAS data. This is the first report of this phenomenon in lodgepole pine, and further supports the use of needle characteristics to assess tree health. [ABSTRACT FROM AUTHOR]

We investigated the effect of western hemlock dwarf mistletoe (Arceuthobium tsugense (Rosend.) G.N. Jones ssp. tsugense) on the 13 year basal area growth of large (>45.7 cm diameter at breast height) western hemlock (Tsuga heterophylla (Raf.) Sarg.) trees in an old-growth forest in southwestern Washington state. We controlled for spatial effects on tree growth by utilizing twenty-seven 0.4 ha plots that had uninfected, lightly, moderately, and severely infected classes of trees present on each plot. Basal area growth was analyzed using analysis of covariance of a randomized block design that was a balanced design with four treatments (infection classes) and 27 replicates (blocks or 0.4 ha plots), with initial diameter as the covariate. Basal area growth was found to be significantly different among the infection classes (F[3,77] = 10.09 and p < 0.0001). Growth of the light and moderate infection classes was not detectably different from growth of uninfected trees. However, severely infected trees grew from 16% to 46% (mean = 36%) less than uninfected trees of the same initial diameter over the period of study (1991–2004). The large trees in this stand did not show growth impacts until they were severely infected. Nous avons étudié l’effet du faux-gui de la pruche (Arceuthobium tsugense (Rosend.) G.N. Jones ssp. tsugense) sur 13 années de croissance en surface terrière de grosses tiges (>45,7cm de diamètre au DHP) de pruches de l’Ouest (Tsuga heterophylla (Raf.) Sarg.) dans une forêt ancienne du sud-ouest de l’État de Washington, aux tats-Unis d’Amérique. Nous avons contrôlé les effets spatiaux en utilisant 27 placettes-échantillons de 0,4 ha qui contenaient toutes des arbres non infectés ainsi que des arbres légèrement, modérément et sévèrement infectés. La croissance en surface terrière a été analysée au moyen d’une analyse de covariance avec un plan expérimental en blocs complètement aléatoires : un plan équilibré avec quatre traitements (classes d’infection) et 27 répétitions (blocs ou placettes-échantillons de 0,4 ha) et le diamètre initial comme covariable. La croissance en surface terrière était significativement différente entre les classes d’infection (F[3,77] = 10,09 et p < 0,0001). Une différence de croissance n’a pas été détectée entre les classes d’infection légère ou modérée et les arbres non infectés. Cependant, les arbres sévèrement infectés ont eu une croissance 16 % à 46 % (moyenne de 36 %) inférieure à celle des arbres non infectés de même diamètre initial au cours de la période d’étude (1991–2004). La croissance des gros arbres dans ce peuplement n’a pas été affectée tant qu’ils n’étaient pas sévèrement infectés. [ABSTRACT FROM AUTHOR]

Rehabilitation of skid trails, temporary roads, and log landings is required for many harvested sites in British Columbia; however, more information is needed regarding practical methods to return these access areas to productive forest. Lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) seedlings (1 + 0) were planted into (i) fully rehabilitated landings (burn-pile debris and topsoil incorporated), (ii) tilled landings, and (iii) unprepared portions of the adjacent cutblock. After two seasons of growth in the field, seedlings planted on fully rehabilitated landings were 38% larger, more robust, and exhibited 44% greater absolute growth and 22% greater relative growth rates, than seedlings planted in the adjacent cutblock. Seedlings planted on tilled landings were 33% smaller, and exhibited absolute growth rates 38% less, and relative growth rates 18% less, than seedlings planted in the adjacent cutblock. Seedlings planted in the cutblock exhibited higher ectomycorrhizal colonization rates. Our results indicate that tillage alone was not sufficient to fully rehabilitate these landings, but that incorporation of recovered topsoil and burn-pile debris produced an excellent growth substrate. This method, using materials found on site, can prevent a significant loss of land regenerating to productive second-growth forest. En Colombie-Britannique, les sentiers de débardage, les chemins temporaires et les jetées doivent être réhabilités dans plusieurs stations après une coupe. Cependant, il faudrait plus d’informations sur les méthodes pratiques pour remettre en production ces zones d’accès. Des semis de pin tordu latifolié (Pinus contorta Dougl. ex Loud. var. latifolia Engelm.) (1 + 0) ont été plantés sur (i) des jetées complètement réhabilitées (débris provenant d’empilements brûlés et incorporation de sol arable), (ii) des jetées labourées et (iii) des portions adjacentes du bloc de coupe non préparées. Après deux saisons de croissance au champ, les semis plantés sur les jetés complètement réhabilitées étaient 38 % plus gros, plus robustes et avaient une croissance absolue 44 % plus grande et un taux de croissance relative 22 % plus élevé que les semis plantés dans le bloc de coupe adjacent. Les semis plantés sur les jetées labourées étaient 33 % plus petits et avaient un taux de croissance absolue 38 % inférieur et un taux de croissance relative 18 % inférieur aux semis plantés dans le bloc de coupe adjacent. Les semis plantés dans le bloc de coupe adjacent avaient un taux de colonisation ectomycorhizienne plus élevé. Nos résultats indiquent que le travail du sol seul n’est pas suffisant pour complètement réhabiliter ces jetées mais que l’incorporation de sol arable récupéré et de débris provenant d’empilements brûlés a produit un excellent substrat de croissance. Cette méthode, qui a recours à des matériaux trouvés sur place, peut prévenir d’importantes pertes de terrains qui, en se régénérant, supporteront une forêt de seconde venue productive. [ABSTRACT FROM AUTHOR]

Studies the collection and storage of seeds of Arceuthobium americanum from Pinus banksiana infected with lodgepole pine dwarf mistletoe. Productivity of seed collection at widely separated sites; Efficacy of using stockinet as a collection material; Germinative ability of seed in storage.

The article presents abstracts on plants which include the globular embryo formation of arceuthobium americanum, the need for an intact cuticle to induce arabidopsis' acquired resistance, and the disturbance caused by cucumber mosaic virus to respiratory and photosynthetic electron transport.