Bidirectional introgression between loblolly pine (Pinus taeda L.) and shortleaf pine (P. echinata Mill.) has increased since the 1950s

Hybridization between loblolly pine and shortleaf pine has been shown in sympatric and allopatric portions of the species native ranges. In this study, we used 25 microsatellite markers to determine the hybrid status of 165 and 151 loblolly pine and shortleaf pine trees sampled across their ranges, respectively, and to estimate population differentiation within these species. Estimated differentiation (?? _PT) for these current-day samples was significantly higher in both species??0.115 in loblolly pine and 0.146 in shortleaf pine??than for trees planted from seed collected from the same locations in the 1950s. These increases are likely due to anthropogenic causes such as habitat fragmentation. In addition, the proportion of hybrids rose dramatically in both species: 27.3% hybrids in loblolly pine populations and 46.7% hybrids in shortleaf pine populations compared to rates of 4.5% and 3.3%, respectively, in the 1950s populations. Our results suggest that shortleaf pine and remnant naturally regenerated loblolly pine are at risk.     

Natural hybridization within seed sources of shortleaf pine (Pinus echinata Mill.) and loblolly pine (Pinus taeda L.)

Shortleaf and loblolly pine trees (n = 93 and 102, respectively) from 22 seed sources of the Southwide Southern Pine Seed Source Study plantings or equivalent origin were evaluated for amplified fragment length polymorphism (AFLP) variation. These sampled trees represent shortleaf pine and loblolly pine, as they existed across their native geographic ranges before intensive forest management. Using 17 primer pairs, a total of 96 AFLPs between shortleaf pine and loblolly pine were produced and scored on the sample trees and two control-pollinated F1 interspecies hybrids and their parents. In addition, the well known isocitrate dehydrogenase (IDH) isozyme marker was scored for all trees. IDH detected two putative hybrids among the loblolly pine samples and two among the shortleaf pine samples, while either 13 or 12 putative hybrids were detected using all AFLP markers and IDH and either NewHybrids or Structure software, respectively. Results of this study show that later generation hybrids can be reliably identified using AFLP markers and confirmed that IDH is not a definitive marker for detecting hybrids; that is, at least in some seed sources, the alternative species’ IDH allele resides in the source species. Based on all the markers, hybridization frequency varied geographically, ranging from 30% in an Arkansas seed source to 0% in several other seed sources. The hybridization level was higher in populations west of the Mississippi River than in populations east of the river; the shortleaf pine hybridization rates were 16.3% and 2.4% and the loblolly pine rates were 4.5% and 3.3%, west and east of the river, respectively. The results suggest that hybridization between these two species is significant but varies by seed source and species, and the potential for the unintended creation of hybrids should be considered in forest management decisions regarding both natural and artificial regeneration.     

Recovery from topkill of shortleaf pine × loblolly pine hybrids compared to their parent populations

Hybrids between shortleaf pine (Pinus echinata Mill.) and loblolly pine (Pinus taeda L.) have increased since the 1950s throughout the southeastern USA. Previously, greater sprouting capacity and the formation of a basal crook that lowers the height of dormant buds may have favored pure shortleaf pine populations on fire prone sites. The objective of this study was to determine how seasonal timing of topkill by both fire and topclipping affect sprouting of shortleaf × loblolly pine F1 hybrids compared to their parent open-pollinated populations during their third growing season. A factorial combination of top-clipping (hand pruners) and girdling by fire (propane torch) was conducted on November 2010, January, March, and April 2011 and sprouting response was measured after the growing season. Survival of topkilled shortleaf pine (94 %) was greatest followed by hybrid (78 %) and loblolly pine (35 %). However, species effects varied with topkill treatment and treatment date because survival was relatively lower for loblolly and hybrid pines in the burn-only as well as the November and April treatment dates while survival of shortleaf pine was consistently high. The number of sprouts was greatest for shortleaf (32.3) intermediate for hybrid (23.8) and lowest for loblolly pine (12.0). Overall, 83 % of shortleaf pine, 35 % of hybrid pine, and 5 % of loblolly pine exhibited a basal crook. The height from ground line to the lowest sprout was shortest for shortleaf (3.5 mm), intermediate for hybrids (7.7 mm), and largest for loblolly pine (21.3 mm). While the hybrid saplings exhibited intermediate performance in survival, sprouting capacity, and crooking, pure shortleaf pine were superior and are probably better suited to recover from fire.     

Paternal chloroplast inheritance patterns in pine hybrids detected with trnL-trnF intergenic region polymorphism

The inheritance patterns of the chloroplast genomes of shortleaf pine (Pinus echinata Mill.), loblolly pine (Pinus taeda L.) and slash pine (Pinus elliottii Engelm.) were investigated through the trnL-trnF intergenic spacer polymorphism analysis. The DNA sequences of this spacer differ among these three closely related Pinus species. A modified 'cold' PCR-SSCP (single-strand conformation polymorphism) analysis of this spacer shows that the artificial hybrids (F1) from the shortleaf pine (seed parent) 2 loblolly pine (pollen parent) cross, exhibit the loblolly pine profile. Additionally, nine putative hybrids between shortleaf pine and loblolly pine, previously identified by the IDH (Isocitrate dehydrogenase) allozyme marker, presented the shortleaf pine profile indicating that shortleaf pine, not loblolly pine, sired all of the putative hybrids. Nondenatured polyacrylamide-gel electrophoresis of the trnL-trnF intergenic spacer demonstrated that the artificial hybrids (F1) from the cross, slash pine (seed parent) 2 shortleaf pine (pollen parent), present the shortleaf pine profile. Those results confirmed that the chloroplast genome is paternally inherited in these three species of the genus Pinus. The significance of the trnL-trnF intergenic region polymorphism and our modified 'cold' SSCP protocol for population genetic studies is discussed.     

Micropropagation of shortleaf,Virginia and loblolly x shortleaf pine hybrids via organogenesis

Protocols were developed for the micropropagation of shortleaf pine (Pinus echinata Mill.), loblolly (P. taeda L.) x shortleaf pine hybrids, and Virginia pine (P. virginiana Mill.). For meristematic tissue induction, modified Gresshoff & Doy (GD) medium with a high concentration of benzyladenine (BA) and short pulse treatment was best for loblolly x shortleaf hybrids whereas a lower concentration of BA and longer pulse treatment was best for shortleaf and Virginia pines. Shoot growth rate for all species was generally slower on Schenk & Hildebrandt medium than on GD medium. Addition of activated charcoal improved shoot growth of shortleaf pine but not of Virginia pine or the loblolly x shortleaf hybrids. Separation of shoots was beneficial before placing in the advanced growth medium. Both GD and Litvay's media produced good advanced shoot growth, especially following the addition of 0.5% activated charcoal. Individual shoot heights of 2–3 cm and 8–12 weeks of age after separation from the cluster were best for rooting. Root induction declined rapidly thereafter. Modified GD medium with 0.5 mg 1^-1 -naphthaleneacetic acid plus 1.0 mg 1^-1 3-indolebutyric acid and 20 g 1^-1 sucrose was best for root induction for all species except shortleaf pine. Addition of activated charcoal produced better root systems. Too high a light intensity resulted in a lowered frequency of rooting. A large number of plantlets was produced.     

Genetic diversity within and among populations of shortleaf pine (Pinus echinata Mill.) and loblolly pine (Pinus taeda L.)

Shortleaf pine (n = 93) and loblolly pine (n = 112) trees representing 22 seed sources or 16 physiographic populations were sampled from Southwide Southern Pine Seed Source Study plantings located in Oklahoma, Arkansas, and Mississippi. The sampled trees were grown from shortleaf pine and loblolly pine seeds formed in 1951 and 1952, prior to the start of intensive forest management across their native ranges. Amplification fragment length polymorphism (AFLP) markers were developed and used to study genetic diversity and its structure in these pine species. After screening 48 primer pairs, 17 and 21 pairs were selected that produced 794 and 647 AFLPs in shortleaf pine and loblolly pine, respectively. High-AFLP-based genetic diversity exists within shortleaf pine and loblolly pine, and most (84.73% in shortleaf pine; 87.69% in loblolly pine) of this diversity is maintained within physiographic populations. The high value of unbiased measures of genetic identity and low value of genetic distance for all pairwise comparisons indicates that the populations have similar genetic structures. For shortleaf pine, there was no significant correlation between geographic distance and genetic distance (r = 0.28), while for loblolly pine there was a weak but significant correlation (r = 0.51).     

Microsatellite versus AFLP analyses of pre-management introgression levels in loblolly pine (<Emphasis Type="Italic">Pinus taeda</Emphasis> L.) and shortleaf pine (<Emphasis Type="Italic">P. echinata</Emphasis> Mill.)

Loblolly pine and shortleaf pine are known to naturally hybridize. In this study, we used 42 microsatellite markers and isocitrate dehydrogenase isozyme to create genetic profiles of 202 loblolly and shortleaf pine trees grown from seed collected in the 1950s for the Southwide Southern Pine Seed Source Study. Estimated Φ_PT was low in both loblolly (0.061) and shortleaf (0.080) pines, indicating that most of the diversity is accounted for within seed sources. However, both loblolly and shortleaf pines showed significant correlations between seed sources’ genetic and geographic distances, with R ² of 0.43 and 0.17, respectively. The hybridization rate was 4.0%, with more hybrids west of the Mississippi River (8.1%) than east of the river (2.1%). Additionally, about the same proportion of both species (4.5% of loblolly and 3.3% of shortleaf pine) were identified as hybrids. These results are consistent with prior studies on these two species but do contrast with the results from an amplified fragment length polymorphism (AFLP) analysis of the same samples. For example, the AFLP study concluded that 6.3% of the trees were hybrids, or 1.4 times higher than determined by this study. Of the 12 hybrids identified in the AFLP study, six were not identified as hybrids here, and of the eight hybrids identified here, only four were identified in the AFLP study. Although similar in overall results, we suggest that the microsatellite analysis is more convincing than the AFLP analysis because microsatellites provide more information per genetic locus than do AFLPs.     

The genetics of shortleaf pine (<Emphasis Type="Italic">Pinus echinata</Emphasis> mill.) with implications for restoration and management

Shortleaf pine (Pinus echinata Mill.) is an important commercial timber resource and forest ecosystem component in the southeastern USA. The species occurs in mainly drier sites as an early- to mid-successional species, is fire-adapted, and it plays an important role in the fire ecology of the region. However, shortleaf pine genetics are not well-studied, especially in this era of molecular genetics and genomics. Most genetics research about the species has focused on provenance testing. Generally, shortleaf pine performs well in colder areas, when compared to loblolly pine (Pinus taeda L.), a close relative, which is faster growing and the most common plantation species in the region. Though not as advanced in genetic improvement as loblolly pine, tree breeders have improved shortleaf pine in one to two generations of selection, and diverse, genetically improved shortleaf pine materials are available to foresters and landowners throughout the southeastern USA. Researchers have also studied the genetic variation of shortleaf pine using various molecular markers and have found that shortleaf pine is generally a prolific outcrosser, a trait it shares with other non-isolated members of the family Pinaceae. In recent years, however, it has shared less genetic material across long ranges, probably because of habitat fragmentation. Various anthropogenic factors also affect shortleaf pine’s future, as recent studies show that shortleaf pine introgression with loblolly pine puts the species—and the resiliency of southeastern forests—at risk. Importantly, fire exclusion is a likely cause of the increase in introgression. Herein, we provide further details and up-to-date genetic information and resources for foresters and ecologists interested in the restoration and management of shortleaf pine.     

Hyphal growth of Phytophtora cinnamomi on pine callus tissue

A procedure was developed which demonstrates the expression of differential resistance in pine callus tissues to the fungal pathogen Phytophthora cinnamomi Rands. Callus tissues were maintained on a modified Murashige and Skoog medium with 10^–5M 2,4-D and inoculated with hyphae of P. cinnamomi at 26°C in the dark. The number of intracellular hyphae was used as an index of resistance. Loblolly and loblolly × shortleaf pine hybrids were determined to be more resistant to infection and invasion by the fungus than were shortleaf and Virginia pine.Abbreviations (AL) loblolly pine—Alabama - (PL) South Carolina - (AS) shortleaf pine—Alabama - (CS) Georgia - (AV) Virginia pine—Alabama - (H1) loblolly × shortleaf pine hybrids—14–42 × 6-I-43 - (H2) I-523 × 6-D-8     

Population structure and growth-stress relationship of Pinus taeda in rock outcrop habitats

Abstract. On the granite outcrops of the southeastern United States, soil accumulates in shallow depressions on the rock surface. A specific sequence of vascular plants characterizes the temporal development of these systems. The edaphic end point of the succession is apparently attained with a herb-shrub-tree stage with Pinus taeda as the dominant tree. We studied the characteristics of this stage and the population structure of P. taeda on outcrop islands in order to specify the successional status of the species in this habitat. We compared the radial growth pattern of outcrop and Piedmont populations of P. taeda, and of two outcrop sub-populations. We checked whether trees on outcrops experience more limiting conditions than trees on the Piedmont, and studied the recent change in the relationship between growth and stress (e.g. drought and atmospheric deposition) reported for loblolly pine in the southeastern United States. We also attempted to identify the climatic variables most critical for tree growth on outcrops. On outcrop soil islands, P. taeda maintains populations that are of irregular age distribution, possibly in response to irregular recruitment and survival. There are no signs of loblolly pine replacement by hardwood species on any of the islands studied, although an understory of shrubby oak appears to characterize larger and deeper-soil islands. Although trees on the Piedmont were growing at a higher rate than those on the outcrop in the first part of the 1950–1988 period, their growth declined at a higher rate than that of trees on the outcrop. As a result, at the end of the period considered (1950–1988), the differences in radial growth between outcrop and Piedmont populations were relatively small. On the outcrop, trees < 22 yr old in 1989 were growing at a rate somewhat lower than that of trees of similar age, 40 yr ago. Differences were apparent in the initial growth patterns between the two outcrop subpopulations (1989 and 1949 stems), and these could have resulted from differences in competition regime, stress or climatic conditions, or a combination thereof. However, a repeated-measures ANOVA failed to reveal a significant recent decrease in the radial growth of loblolly pine in the system studied. The identification of numerous signature years (years with ≥ 80 % of the trees with similar increasing or decreasing trend in their radial growth) suggests that similar environmental variables control the growth of loblolly pine in both outcrop and Piedmont habitats. High temperature and low precipitation in the first part of the summer (June-July) seem to limit radial growth. Those pines growing on outcrop soil islands, however, appear more sensitive to climatic fluctuations.     

Characterization of phosphorus uptake in slow- and fast-growing southern pine seedlings grown in solution culture

The effects of low-P growth conditions on growth and net P acquisition were examined in two species of pine that are indigenous to P-deficient soils of the Atlantic Coastal Plain: pond pine (Pinus serotina Michx.), a moderately-fast growing pine, and a slow-growing seed source of loblolly pine P. taeda L.) from Texas. Short-term ³²P uptake experiments were conducted using intact nonmycorrhizal seedlings that had been grown for 7 weeks in continuously-flowing solution culture at 5 or 100 µM P. Growth and P uptake of pond pine were more responsive to a higher P supply than the slow-growing loblolly pine. Pond pine seedlings in the 100 µM P treatment were twice the size of those grown in 5 µM P and accumulated almost five times as much seedling P. In contrast, seedling biomass of loblolly pine increased by only 8% under high-P growth conditions, and seedlings accumulated twice as much P, reflecting the higher P concentrations in shoot and root tissues. Although rates of unidirectional influx of ³²P were 22 and 61% higher under low-P growth conditions in pond and loblolly pine, respectively, net uptake rates in seedlings from the 5 µM P treatment were over three times those of seedlings grown in 100 µM P. These results suggest that unidirectional efflux out of the root was controlling net uptake of P as much, if not more, than unidirectional influx. Efflux of³² P out of root tissue, particularly older tissue, decreased in seedlings grown under low-P conditions, possibly due to a reduction in the size of the phosphorus pool available for efflux, i.e. the soluble P_i pool. Over 75% of the total root P in both loblolly and pond pine seedlings grown in 100 µM P treatment was present as organic P, suggesting that organic P, particularly phytate, may represent important storage pools in roots of woody species. Within each species, higher rates of influx and net uptake in seedlings from the low-P treatment were associated with lower P concentrations in shoot and root tissue, and shoot FW:root FW ratios. Efflux may represent a short-term means of regulating net P uptake, while the demand for P created by growth and storage may represent a long-term regulation.     

Aerenchyma and lenticel formation in pine seedlings: A possible avoidance mechanism to anaerobic growth conditions

Seedlings of pond pine ( Pinus serotina Michx.), sand pine [ P. clausa (Engelm.) Sarg.], and loblolly pine ( P. taeda L., wet-site and drought-hardy seed sources) were grown in hydroponic solution culture using a non-circulating, continuously flowing design under anaerobic or aerobic conditions to determine whether flooding tolerance was correlated with enhanced internal root aeration. Transport of atmospheric O₂ from the shoot to the root of anaerobically grown loblolly and pond pine seedlings was demonstrated via rhizosphere oxidation, using both reduced indigo-carmine solution and a polarographic, ensheathing Pt-electrode. Stem and root collar lenticels were the major sites of atmospheric O₂ entry for submerged roots in these seedlings. No O₂ leakage was detected from roots of aerobically grown pine seedlings. Longitudinal and radial pathways for gaseous diffusion via intercellular air spaces in the pericycle and between ray parenchyma cells, respectively, were demonstrated histo-logically in anaerobically grown loblolly and pond pines. Rhizosphere oxidation, and lenticel and aerenchyma development in roots of flood-intolerant sand pine seedlings grown in anaerobic solutions were minimal. Only 15 days of anaerobic growth conditions were necessary to increase internal root porosities of loblolly and pond pine seedlings – although not to the extent found in seedlings treated for 30 or 75 days. Histological results indicated that root tissue in the secondary stage of growth was capable of forming intercellular air spaces, demonstrating a degree of internal plasticity – at least in the more flood-tolerant loblolly and pond pine seedlings.     

Paternal inheritance of chloroplast DNA and maternal inheritance of mitochondrial DNA in loblolly pine

Summary The inheritance of organelle DNAs in loblolly pine was studied by using restriction fragment length polymorphisms. Chloroplast DNA from loblolly pine is paternally inherited in pitch pine x loblolly pine hybrids. Mitochondrial DNA is maternally inherited in loblolly pine crosses. The uniparental inheritance of organelle genomes from opposite sexes within the same plant appears to be unique among those higher plants that have been tested and indicates that loblolly pine, and possibly other conifers, must have special mechanisms for organelle exclusion or degradation or both. This genetic system creates an exceptional opportunity for the study of maternal and paternal genetic lineages within a single species.     

Large-scale asymmetric introgression of cytoplasmic DNA reveals Holocene range displacement in a North American boreal pine complex

Jack pine (Pinus banksiana) and lodgepole pine (Pinus contorta var. latifolia) are two North American boreal hard pines that hybridize in their zone of contact in western Canada. The main objective of this study was to characterize their patterns of introgression resulting from past and recent gene flow, using cytoplasmic markers having maternal or paternal inheritance. Mitochondrial DNA (mtDNA) and chloroplast DNA (cpDNA) diversity was assessed in allopatric populations of each species and in stands from the current zone of contact containing morphological hybrids. Cluster analyses were used to identify genetic discontinuities among groups of populations. A canonical analysis was also conducted to detect putative associations among cytoplasmic DNA variation, tree morphology, and site ecological features. MtDNA introgression was extensive and asymmetric: it was detected in P. banksiana populations from the hybrid zone and from allopatric areas, but not in P. contorta populations. Very weak cpDNA introgression was observed, and only in P. banksiana populations. The mtDNA introgression pattern indicated that central Canada was first colonized by migrants from a P. contorta glacial population located west of the Rocky Mountains, before being replaced by P. banksiana migrating westward during the Holocene. In contrast, extensive pollen gene flow would have erased the cpDNA traces of this ancient presence of P. contorta. Additional evidence for this process was provided by the results of canonical analysis, which indicated that the current cpDNA background of trees reflected recent pollen gene flow from the surrounding dominant species rather than historical events that took place during the postglacial colonization.     

引种火炬松家系的速生性和稳定性综合分析

以湿地松和马尾松为对照,对福建省引种的5年生火炬松家系生长情况进行调查分析,结果表明,引种火炬松的树高、胸径和材积的家系方差及家系与地点互作方差均达显著水平,火炬松家系在福建省的平均生长表现优于马尾松和湿地松。利用系统聚类法可将测试的25个火炬松家系分为速生、较速生、中等和较差4类,其相对于当地树种马尾松的实际增益分别为83.2%、63.4%、48.5%和33.7%。运用基因型分组法对火炬松家系的速生性和稳定性进行综合评价,最终确定19、25、18、21、10号家系为增产且变异小,具有理想基因型的稳定型家系。     

Relative Susceptibility of Four Pine Species to Infection by Pinewood Nematode

Mature trees of eastern white, jack, Scotch, and shortleaf pines were inoculated with 25,000-34,000 pinewood nematodes, Bursaphelenchus xylophilus, isolated from infected Scotch pines in Missouri. Equal numbers of trees of each species inoculated with distilled water served as controls. Nine of fifteen Scotch pines died within 4 months of nematode infection or during the winter and early spring following infection. A single eastern white and shortleaf pine died. No jack pines died. A single Scotch pine control died, apparently the result of natural nematode infection. No other controls died. Mean oleoresin flow did not differ among nematode-inoculated jack and shortleaf pines and their respective controls. Oleoresin flow in nematode-inoculated eastern white and Scotch pines was significantly lower than in their controls. Oleoresin flow was temporarily reduced in mortality-resistant eastern white and Scotch pines following nematode infection. Thus a sublethal impact of nematode infection on mortality-resistant host trees was documented.     

The effects of ferulic acid on the mineral nutrition of grain sorghum

The combined effects of whole-tree harvesting (WTH) and soil leaching by both acid deposition and naturally-produced carbonic acid were evaluated in a mixed oak and a loblolly pine forest growing on similar soils in the Ridge and Valley province of eastern Tennessee. It was hypothesized that nutrient export via WTH would be greater in a mixed oak stand than in the loblolly pine stand because of greater nutrient concentrations in oak and hickory species than in pine. This hypothesis was true for N,P, and particularly Ca at the time of harvest, but not for K or Mg. When expressed on an annual basis, exports of N,P,K, and Mg were greater in the loblolly pine site and only Ca export was greater in the mixed oak site. It was also hypothesized that the large accumulation of Ca in the oak and hickory vegetation would cause lower exchangeable Ca²⁺ in soils, and, consequently, lower Ca²⁺ leaching in the mixed oak site than in the loblolly pine site. This hypothesis was supported by the data, which indicated 340–370% more exchangeable Ca and 100% more Ca²⁺ leaching in the loblolly pine site than in the mixed oak site. Research sponsored by the U.S. Environmental Protection Agency under Interagency Agreement No. 79-D-X0533 and Biofuels and Municipal Waste Technology Division, U.S. Department of Energy, under Contract No. De-AC05-84OR21400 with Martin Marietta Energy Systems, Inc. Publication No. 2933, Environmental Sciences Division, ORNL.     

Changes in leaf expansion and epidermal screening effectiveness in Liquidambar styraciflua and Pinus taeda in response to UV-B radiation

Absorption or screening of ultraviolet-B (UV-B) radiation by the epidermis may be an important protective method by which plants avoid damage upon exposure to potentially harmful UV-B radiation. In the present study we examined the relationships among epidermal screening effectiveness, concentration of UV-absorbing compounds, epidermal anatomy and growth responses in seedlings of loblolly pine (Pinus taeda L.) and sweetgum (Liquidambar styraciflua L.). Seedlings of each species were grown in a greenhouse at the University of Maryland under either no UV-B radiation or daily supplemental UV-B radiation levels of 4, 8 or 11 kJ m^?2 of biologically effective UV-B (UV-B_BE) radiation. Loblolly pine seedlings were subsequently grown in the field under either ambient or supplemental levels of UV-B radiation. At the conclusion of the growing season, measurements of epidermal UV-B screening effectiveness were made with a fiber-optic microprobe. In loblolly pine, less than 0.5% of incident UV-B radiation was transmitted through the epidermis of fascicle needles and about 1% was transmitted in primary needles. In contrast, epidermal transmittance in sweetgum ranged from about 20% in leaves not preconditioned to UV-B exposure, to about 10% in leaves grown under UV-B radiation. The concentration of UV-absorbing compounds was unaffected by UV-B exposure, but generally increased with leaf age. Increases in epidermal thickness were observed in response to UV-B treatment in loblolly pine, and this accounted for over half of the variability in UV-B screening effectiveness. In spite of the low levels of UV-B penetration into the mesophyll, delays in leaf development (both species) and final needle size (loblolly pine) were observed. Seedling biomass was reduced by supplemental UV-B radiation in loblolly pine. We hypothesize that the UV-induced growth reductions were manifested by changes in either epidermal anatomy or epidermal secondary chemistry that might negatively impact cell elongation.     

Population structure of a lodgepole pine (Pinus contorta) and jack pine (P. banksiana) complex as revealed by random amplified polymorphic DNA.

We studied the population structure of a lodgepole (Pinus contorta Dougl.) and jack pine (Pinus banksiana Lamb.) complex in west central Alberta and neighboring areas by assessing random amplified polymorphic DNA (RAPD) variability in 23 lodgepole pine, 9 jack pine, and 8 putative hybrid populations. Of 200 random primers screened, 10 that amplified 39 sharp and reproducible RAPDs were chosen for the study. None of the 39 RAPDs were unique to the parental species. RAPD diversity ranged from 0.085 to 0.190 among populations and averaged 0.143 for lodgepole pine, 0.156 for jack pine, 0.152 for hybrids, and 0.148 for all 40 populations. The estimated population differentiation based on G(ST) was 0.168 for hybrids, 0.162 for lodgepole pine, 0.155 for jack pine, and 0.247 across all 40 populations. Cluster analysis of genetic distances generally separated jack pine from lodgepole pine and hybrids, but no division could be identified that further separated lodgepole pine from hybrids. The observed weak to mild trend of "introgression by distance" in the complex and neighbouring areas was consistent with the view that introgressive hybridization between lodgepole and jack pines within and outside the hybrid zone may have been through secondary contact and primary intergradation, respectively.