Breeding eastern white pine: A world-wide perspective

Eastern white pine (Pinus strobus L.) has wide genetic variability and high productivity in plantations in North America, Europe and the Far East. In regions where neither white pine blister rust nor the white pine weevil are a problem, as in the central states of the U.S.A. and the warmer parts of Europe, primary attention is given to selection and breeding for vigor. Estimates for trees up to age 18 indicate that a first-generation genetic gain in volume of over 20% can be obtained from open-pollinated family selection within stands. Volume gains of 50% or more over local genotypes have been realized at ages 15–20 through the use of seed from selected southern Appalachian stands and in some individual tree crosses of eastern white pine with blue (Himalayan) pine. In the cool, humid regions of eastern North America and Europe, where blister rust resistance is important, breeding strategies include cloning of resistant P. strobus individuals, use of blue and Balkan pines in breeding programs, and exploitation of low-level rust resistance in low-risk localities. Eastern white pine losses from blister rust can be avoided in Japan and Korea by good plantation management without genetic selection. In some regions where the white pine weevil is the major problem, western white pine is useful both for hybridization and as an alternative, more weevil-resistant species. Analysis of relative photosynthesis of SO₂- and O₃-fumigated clones may be useful as a method of screening for pollution tolerance in regions where air pollution is likely to intensify. Efficient techniques for cloning by rooting of cuttings are now available. Efforts are under way to develop technology for micropropagation for mass production of superior clones. Breeding strategies for the major P. strobus plantation regions of the world are summarized.     

Winter water relations of New England conifers and factors influencing their upper elevational limits. I. Measurements

The upper elevational limits of tree species are thought to be controlled by abiotic factors such as temperature and the soil and atmospheric conditions affecting plant water status. We measured relative water contents (RWC), water potentials (Psi) and cuticular conductances (g(c)) of shoots of four conifer species-eastern hemlock (Tsuga canadensis (L.) Carr.), eastern white pine (Pinus strobus L.), red pine (P. resinosa Ait.) and red spruce (Picea rubens Sarg.)-during two winters on Mt. Ascutney, Vermont, USA. Some micrometeorological measurements are also reported. Eastern hemlock and white pine were studied near their upper elevational limits at a 640-m site, and red pine was studied near its upper elevational limit at 715 m. Red spruce was also studied at the 715-m site, which is in the middle of its elevational range on this mountain. There was no evidence of winter desiccation stress in any species. The observed distribution of seedlings suggested that the upper elevational limits on shade-intolerant eastern white pine and red pine are set by the absence of suitable seed beds after 100 years without fire. Eastern hemlock is able to reproduce in deep shade on organic substrates, but germination at high elevations may be restricted by low temperatures.     

Histopathology of primary needles and mortality associated with white pine blister rust in resistant and susceptible Pinus strobus

White pine blister rust caused by Cronartium ribicola is a damaging non‐native disease of five‐needled pines in North America. Efforts to control the disease and mitigate damage to date have been only somewhat effective. Recent efforts to improve the health of eastern white pine and reestablish the tree as a dominant species in the North Central United States have focused on identification and propagation of disease‐free eastern white pine (Pinus strobus) growing in areas with a high incidence of blister rust. Many of these selections have been shown to resist infection following artificial inoculation with C. ribicola. In this study, 13 eastern white pine families derived from controlled pollination of selections previously determined to possess putative resistance as well as susceptible selections were inoculated with C. ribicola. Mortality data from inoculation studies show superior survivability in three families with over 60% of seedlings able to survive the 52 week post‐inoculation monitoring period compared to 0–10% survival of the most susceptible families. Primary needles were collected for histological analysis from all inoculated families 4 weeks after inoculation and from selected families 6.5 weeks and 38 weeks after inoculation. Histological observations of infection sites show distinct resistance reactions in the families more likely to survive infection based on mortality data. Analysis of the reactions in susceptible families revealed extensive hyphal colonization of the vascular bundle and adjacent mesophyll cells that appear uninhibited by tree responses. In resistant families, collapsed cells adjacent to infection sites, heavy deposition of phenolic compounds and abnormal cell growth were documented more frequently and appear to play an integral role in the ability of these eastern white pine families to impede growth of C. ribicola in primary needle tissue.     

Blister rust in maritime pine

Maritime pine (Pinus pinaster Ait.) seedlings from four stands of central Italy were inoculated with a suspension of 75,000 basidiospores/ml. Significant differences among the stands were found for the following traits: percentages between nonspotted and inoculated seedlings; and percentages between seedlings with spermagonia of Cronartium flaccidum and spotted seedlings. Genetic variation in blister rust resistance among the stands and among the families within a stand confirms the validity of the idea to select the stands which are exposed to heavy rust infection and then within the selected stands to choose trees able to supply the highest possible number of nonspotted seedlings and seedlings with needle spots but without spermagonia.     

Relationships among cold hardiness, root growth potential and bud dormancy in three conifers

Greenhouse-cultured, container-grown ponderosa pine (Pinus ponderosa var. scopulorum Engelm.), interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) and Engelmann spruce (Picea engelmannii (Parry) Engelm.) were cold acclimated and deacclimated in growth chambers over 19 weeks. Stem cold hardiness, total new root length at 14 days and days to bud break were measured weekly. Relationships among cold hardiness, root growth potential (RGP) and bud dormancy suggest that cold hardiness, which can be measured quickly, could provide a useful basis for estimating the two other parameters. During cold acclimation, there was a lag period in which stem cold hardiness remained at -15 degrees C and RGP was at a minimum, in all three species. Douglas-fir and Engelmann spruce buds remained fully dormant during this lag period. Ponderosa pine buds had no chilling requirement for the loss of dormancy, and reached quiescence during the lag period. Immediately following the lag period, as stem cold hardiness progressed to -22 degrees C, RGP increased to a high plateau in all three species, and Douglas-fir and Engelmann spruce buds approached quiescence. Cold deacclimation and bud development began immediately on exposure to warm, long days, but RGP remained high until stem cold hardiness returned to approximately -15 degrees C. At bud break, cold hardiness and RGP were at the minimum.     

Assessment of seedling storability of Quercus robur and Pinus sylvestris

Pedunculate oak (Quercus robur L.) and Scots pine (Pinus sylvestris L.) seedlings were lifted on several occasions during autumn 1997 to determine the relationships between storability and frost hardiness. On each lifting date their physiological status was determined by assessment of shoot and root electrolyte leakage and frost hardiness, assessed as freeze-induced electrolyte leakage. Additional seedlings were simultaneously cold-stored for field planting and assessment of preplanting root growth potential in April 1998. First year field performance was determined the following winter. Storability and cold acclimation patterns differed between the two species. Both were negatively affected by early lifting, but oak was less sensitive with respect to survival, and pine attained tolerance to cold storage more rapidly and earlier with respect to growth increment. The correlations between shoot frost hardiness and performance suggest that freeze-induced shoot electrolyte leakage (SEL_diff?20) below a threshold of 5% is a good storability predictor for Scots pine in Denmark. A completely reliable criterion for pedunculate oak could not be established.     

Seedling cold hardiness, bud set, and bud break in nine provenances of Pinus greggii Engelm.

Cold hardiness and timing of bud set and bud break are important processes that provide protection of nursery seedlings against low temperatures. Seedlings of 9 provenances of Pinus greggii from two different regions of Mexico were tested to determine cold hardiness, bud set, and bud break timing differences. Needle sections were exposed to freezing temperatures to determine an injury index of each provenance. In addition, bud set and bud break timing were recorded through the fall, winter and spring. There were significant differences in cold hardiness between seedlings from northern and southern provenances. At the maximum cold hardiness, the index of injury (LT₅₀) for northern provenances was LT₅₀ = −18 °C, compared to −12 °C for southern provenances. There was a considerable variation among the provenances in the proportion of seedlings that set terminal buds. Seedlings from northern provenances had greater proportions of seedlings that set a terminal bud than seedlings from southern provenances. There were also significant differences in the bud break timing in the following spring among the 9 provenances. Seedlings from northern provenances broke bud earlier than southern provenances. Cold hardiness, bud set, and bud break timing results may be useful to determine how far a specific seed source can be moved from its natural environment.     

Variation of virulence of white pine blister rust

According to the literature the following evidence suggests racial variation in white pine blister rust: changes over site in general level of resistance; interaction of needle spot color types with crosses of western white pine; neutralization of specific resistance reactions; bark reactions and normal cankers on the same tree.     

Comparison of three cold hardiness tests for conifer seedlings

Greenhouse-cultured, container-grown ponderosa pine (Pinus ponderosa var. scopulorum Engelm.), interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco), and Engelmann spruce (Picea engelmannii (Parry) Engelm.) were cold acclimated and deacclimated in growth chambers over 19 weeks. Cold hardiness was measured weekly by a whole-plant freeze test and by two quick tissue tests: freeze-induced electrolyte leakage of needles, and differential thermal analysis of buds. The whole-plant freeze test provided results in 7 days, and indicated differences in cold hardiness among stems, buds, and needles. Although the whole-plant freeze test could accurately measure cold hardiness, it was not precise, and it required destructive sampling. Results from freeze-induced electrolyte leakage and differential thermal analysis were available in 2 days and 1 hour, respectively. The freeze-induced electrolyte leakage test was a precise, sensitive and objective predictor of changes or differences in tissue cold hardiness. To determine actual cold hardiness, results could be calibrated to the response of the same tissue in the whole-plant freeze test. The speed and objectivity of differential thermal analysis made this test useful for rapid, general assessment of cold hardiness status, but calibration was difficult, and precision varied.     

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.     

Relationship between carbohydrate concentration and root growth potential in coniferous seedlings from three climates during cold hardening and dehardening

Greenhouse-cultured, container-grown seedlings of Aleppo pine (Pinus halepensis Mill.), radiata pine (Pinus radiata D. Don), and interior Douglas-fir (Pseudotsuga menziesii var. glauca (Beissn.) Franco) were cold acclimated and deacclimated in growth chambers over 24 weeks. Needle and root cold hardiness and root growth potential (RGP) were measured weekly. Root, needle and stem analyses for soluble sugars and starch were performed biweekly. In all tissues, there was a close correspondence between cold hardiness and the absolute concentration of soluble sugars, as well as between the increase and decrease in concentration of soluble sugars during cold hardening and dehardening, respectively, supporting the theory that soluble sugars function as cryoprotectants in plant tissues. The magnitude of starch concentration did not parallel the magnitude of the cold hardiness attained, and changes in starch concentration were related to production and consumption factors, rather than timing of changes in cold hardiness. The rise and fall of RGP paralleled the rise and fall of total carbohydrate concentration in roots. The behavior of the three species was surprisingly similar, considering the different climates to which they are adapted.     

Morphological characteristics associated with tolerance to competition from herbaceous vegetation for seedlings of jack pine,black spruce,and white pine

Tolerance of bareroot and container-grown seedlings of black spruce (Picea mariana (Mill.) B.S.P.), jack pine (Pinus banksiana Lamb.), and eastern white pine (Pinus strobus L.) to competition from herbaceous vegetation was examined in the first five years after planting on a site in the Great Lakes/St. Lawrence forest of Ontario, Canada. Shoot and root morphological characteristics of various stocktypes were measured before planting and correlated with 5-year survival and growth following control and no control of herbaceous vegetation. For black spruce and jack pine, medium-sized bareroot stocktypes had greater relative 5-year stem volume growth in the presence of herbaceous vegetation than did container stock of either species or large bareroot stock of spruce. Relative volume growth was measured as the ratio of the cumulative stem volume increment in the presence of vegetation (Veg) to that in the absence of vegetation (NoVeg), i.e., the Veg:NoVeg ratio. In white pine, the Veg:NoVeg ratio of volume increment of medium container and large bareroot stocktypes exceeded that of small container and medium bareroot stocktypes. In jack pine, root collar diameter at planting and number of first-order lateral roots were positively correlated with 5-year Veg:NoVeg ratio of volume increment. In white pine, the Veg:NoVeg ratio was also positively correlated with root collar diameter at planting and with root volume. In black spruce, the ratio was not related to pre-plant morphology. Thus, for white pine and jack pine, certain pre-plant morphological features may be useful in forecasting the relative ability of different stocktypes to grow under herbaceous competition conditions in the field.     

Effects of soil organic matter,moisture, shading and ash on white pine (Pinus strobus L.) seedling emergence

The effects of soil organic matter, soil moisture, shading and ash on white pine (Pinus strobus L.) emergence were investigated using soil monoliths in greenhouse experiments. White pine seedling emergence increased with soil organic matter removal, and levelled with the elimination of the litter and fermentation layers, where seedling emergence did not significantly increase further. Increased shade and soil moisture levels also improved seedling emergence whereas ash had no or little impact on white pine seedling emergence. The silvicultural implications of these findings are discussed with regard to white pine management.     

European larch and eastern white pine respond similarly during three years of partial defoliation

To test whether trees with different leaf life spans respond differently to defoliation, eastern white pine (Pinus strobus L.) and European larch (Larix decidua Mill.) trees (9 years old in 1991) were partially defoliated by hand between July 1 and 10 in 1989, 1990 and 1991. At the end of 1991, trees of both species had received either 0, 1, 2 or 3 years of defoliation. Trees that received only 1 year of defoliation were defoliated in 1989. Variables measured included photosynthesis, twig water potential, leaf mass per area and leaf nitrogen concentration. There were few significant responses to defoliation in any of the three years of treatment in either species, and only the current-year defoliation treatments caused significant responses. Both species had reduced photosynthetic rates and less negative twig water potentials in response to defoliation in 1989. In 1990 and 1991, the defoliation treatments had no significant effect on any of the parameters measured in European larch. In 1990, there was a significant reduction in foliar nitrogen concentration in eastern white pine in response to defoliation in 1990. In 1991, eastern white pine had significantly less negative twig water potentials in response to defoliation in 1991. Leaf mass per area was not affected by defoliation in either species. We conclude that, for European larch and eastern white pine, differences in leaf life span have no effect on leaf- and twig-level responses to defoliation.     

Endophyte-mediated resistance against white pine blister rust in Pinus monticola

Induced resistance responses, including fungal endophyte-mediated resistance, have been well studied in both agricultural crops and grass systems. Yet, the effect of these processes and symbionts in forest trees is poorly known. Fungal endophytes have been found in all conifer forest systems examined to date and have been hypothesised to be involved in resistance-mediated responses. However, in the absence of functional studies the influence of these endophytes on the extended phenotype of the host plant is unclear. In this study we demonstrate that fungal endophytes from Pinus monticola were effective at increasing survival in host plants against the exotic pathogen Cronartium ribicola, which is responsible for the devastating disease called white pine blister rust. Seedlings previously inoculated with fungal endophytes lived longer than endophyte-free seedlings and also showed some reduction in white pine blister rust disease severity. This endophyte-mediated resistance was found to be effective over time, indicating persistence, and is hypothesised to be a form of induced resistance. Overall, this suggests fungal endophytes may play a determinative role in the structure of biological communities and could provide a useful alternative or ancillary management tool for combating pests and diseases.     

Fall fertilization of Pinus resinosa seedlings: nutrient uptake, cold hardiness, and morphological development

? Fall fertilization may increase plant nutrient reserves, yet associated impacts on seedling cold hardiness are relatively unexplored.

? Bareroot red pine (Pinus resinosa Ait.) seedlings in north-central Minnesota, USA were fall fertilized at the end of the first growing season with ammonium nitrate (NH₄NO₃) at 0, 11, 22, 44, or 89 kg N ha^?1. Seedling morphology and cold hardiness [assessed by freeze induced electrolyte leakage (FIEL)] were evaluated six weeks after fertilization and following the second growing season.

? Seedling height and number of needle primordia increased with fertilizer rate for both sampling years. Seedlings fertilized with 44 and 89 kg N ha^?1 attained target height (15 cm) after the second growing season. Shoot and root N concentration increased after the first growing season in fall fertilized seedlings compared to controls. Fall fertilized seedlings had lower FIEL (i.e., increased cold hardiness) compared to controls when tested at ?40 °C after the first growing season, but no significant differences in FIEL of control and fertilized seedlings were observed after the second growing season.

? Results suggest that fall fertilization of red pine seedlings can help render desired target height in the nursery, while maintaining or increasing cold hardiness levels.

     

Winter water relations of New England conifers and factors influencing their upper elevational limits. II. Modeling

We used the water relations model, WINWAT, to model winter water relations of three conifer species-eastern hemlock (Tsuga canadensis (L.) Carr.), eastern white pine (Pinus strobus L.) and red pine (P. resinosa Ait.)-growing at their upper elevational limits on Mt. Ascutney, Vermont, USA, in the winters of 1997 and 1999. Modeled relative water contents remained above 60% in the two youngest foliar age classes of all three species during both winters, indicating that desiccation stress in winter is not responsible for setting the upper elevational limits of these species at this site under present climatic conditions. WINWAT indicated that winter water relations of these low-elevational species were sensitive to low relative humidity, which increased transpiration rates, and low temperatures, which inhibited recharge, but are much less sensitive to summer climate than in the case of subalpine conifers in Colorado. Our results indicate that summer and winter temperatures and relative humidities (or precipitation/potential evapotranspiration ratios) should be incorporated into climate change models designed to simulate future tree distributions.     

Comparison of greenhouse and environmentally controlled growthroom root growth potential testing of 2+0 eastern white pine seedlings

Two-year-old estern white pine (Pinus strobus L.) seedlings were measured for Root Growth Potential (RGP) in a hydroponic system over two years in both a greenhouse and an environmentally controlled growthroom. Analyses of variance showed no significant differences (alpha = 0.05) between testing environments for either year. This study demonstrates the validity of using greenhouse RGP testing for 2+0 eastern white pine.     

Relative susceptibility to blister rust caused by Cronartium flaccidum of several species of pine

At Florence, Italy, several species of pine were experimentally infected with blister rust. Inoculations were carried out on 3 and 15 months-old seedlings. After antificial and natural inoculation, Brutia, Aleppo, Austrian, Swiss mountain, Maritime and Italian stone pine showed pyenia and aecia. Spotted seedlings of Ponderosa pine showed only mycelium of C. flaccidum in needle and stem tissues. The exotic species seemed to have a very high degree of resistance to blister rust.