Functional trait recovery through backcross breeding in blister rust–resistant hybrid white pines (Pinus strobus × Pinus wallichiana)

Eastern white pine is highly susceptible to damage from white pine weevil, and to some extent white pine blister rust, in the northeastern United States. Western white pine has shown resistance to the weevil, but is highly susceptible to blister rust in the West. Objectives of this study were to compare the growth and resistance of eastern and western white pine to damage from the weevil and blister rust and to identify families of western white pine suitable for planting in the East. A field trial containing 76 half-sib families of western white pine and two half-sib families of eastern white pine was established in 1983 at two sites, one each in New York and Maine. After 14 yr, tree height and diameters were measured, and resistance to weevil and rust assessed. Tree height and diameters were significantly greater for eastern white pine than western white pine. Western white pine sustained approximately fourfold less weevil damage at both sites, but was more impacted by rust at one site. Cluster and discriminant analyses were used to group families using three variables: height growth, resistance to weevil, and resistance to blister rust. One single group combined superior height growth with moderate resistance to both pests. Selections made from within these families have the most promise for planting western white pine in the East. North. J. Appl. For. 20(1):19–26.

BackgroundPicea species are distributed and planted world-wide due to their great ecological and economic values. It has been reported that Picea species vary widely in growth traits in a given environment, which reflects genetic and phenotypic differences among species. However, key physiological processes underlying tree growth and the influencing factors on them are still unknown.ResultsHere, we examined needle structures, needle chemical components, physiological characteristics and growth traits across five Picea species in a common garden in Tianshui, Gansu province in China: Picea glauca, P. mariana, P. likiangensis, P. koraiensis, and P. crassifolia, among which P. glauca and P. mariana were introduced from North America, P. likiangensis was from Lijiang, Yunan province in China, P. koraiensis was from Yichun, Heilongjiang province in China, and P. crassifolia was native to the experimental site. It was found that nearly all traits varied significantly among species. Tissue-level anatomical characteristics and leaf mass per area (LMA) were affected by needle size, but the variations of them were not associated with the variations in photosynthetic and biochemical capacity among species. Variations in area-based maximum photosynthesis (Pnmax) were affected by stomatal conductance (gs), mesophyll conductance (gm) and biochemical parameters including maximum carboxylation rate (Vcmax), and maximum electron transport rate (Jmax). The fraction of N allocated to different photosynthetic apparatus displayed contrasting values among species, which contributed to the species variations in photosynthetic nitrogen use efficiency (PNUE) and Pnmax. Additionally, all growth traits were positively correlated with Pnmax and PNUE.ConclusionNeedle structures are less important than needle biochemical parameters in determining the variations in photosynthetic capacity across the five Picea species. Pnmax and PNUE are closedly associated with the fraction of N allocated to photosynthetic apparatus (Pphoto) compared with leaf N content per area (Narea). The tremendous growth differences among the five Picea species were substantially related to the interspecies variation in Pnmax and PNUE.

Breeding eastern white pine: A world-wide perspective

SummarySince the arrival to North America ofCronartium ribicola, management of eastern white pine has been driven by the need to avoid the actual or, in many areas, the perceived damage caused by white pine blister rust. Although white pine has lost much of its former dominance, it remains a valuable species for biotic diversity, aesthetics, wildlife habitat and forest products. Understanding its silvics and damaging agents provides a sound basis for the silvicultural activities of site selection, regeneration and stand tending. The species can be successfully grown in many locations despite herbivory, competition, white pine weevil and blister rust. Forest managers can minimize damage by applying knowledge of local conditions (climate, soils, physiography and vegetation) to hazard assessment, site selection and preparation, vegetation management, and pruning. With appropriate management and a long‐term commitment, many eastern forests can be beneficially reforested to eastern white pine with little impact from blister rust and other damaging agents.

Pinus strobus L. (eastern white pine or weymouth pine) is an important timber species of North America. It is one of the about one hundred species of the genus Pinus of the family Pinaceae of the order Coniferae (Mirov, 1967). Like all other species of Pinus, the haploid genome of Pinus strobus consists of 12 chromosomes and its diploid genome has 24 chromosomes. It belongs to the group known as soft pines and is closely related to western white pine (P. monticola Dougl.) and sugar pine (P. lambertiana Dougl.). It occurs in a broad geographical range, from Newfounland and Maritimes across Canada to southeastern Manitoba, through the United States from Minnesota to New England and southward to northern Georgia (Stearns, 1992). Eastern white pine is a relatively long-lived tree and can live for well over 500 years (Stearns, 1992). In old growth forests many eastern white pine trees reach a height of 50 m and a diameter of over 100 cm. Early European explorers reported some white pine trees which were more than 70 m tall and 350 cm in diameter. Early North American timber industry was founded on vast forests of eastern white pine growing in the great lakes region. Today the importance of eastern white pine has declined considerably in the North American timber industry. This has been partially due to the susceptibility of this species to a number of diseases and pests, the chief among which are the white pine blister rust (Cronortium ribicola J.C. Fisch.) and white pine weevil (Pissodes strobi [Peck]) (Jones, 1992). Efforts for genetic improvement of eastern white pine have been concentrated on developing clones and hybrids which are resistant to blister rust (Zsuffa, 1985).KeywordsSomatic EmbryoSomatic EmbryogenesisZygotic EmbryoFemale GametophyteEmbryogenic TissueThese keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Climate-related variations in functional traits of boreal tree species can result both from physiological acclimation and genetic adaptation of local populations to their biophysical environment. To improve our understanding and prediction of the physiological and growth responses of populations to climate change, we studied the role of climate of seed origin in determining variations in functional traits and its implications for tree improvement programs for a commonly reforested boreal conifer, white spruce (Picea glauca (Moench) Voss). We evaluated growth, root-to-shoot ratio (R/S), specific leaf area (SLA), needle nitrogen (N(mass)), total non-structural carbohydrates (NSC) and photosynthetic traits of 3-year-old seedlings in a greenhouse experiment using seed from six seed orchards (SO) representing the different regions where white spruce is reforested in Québec. Height and total dry mass (TDM) were positively correlated with photosynthetic capacity (A(max)), stomatal conductance (g(s)) and mesophyll conductance (g(m)). Total dry mass, but not height growth, was strongly correlated with latitude of seed origin (SO) and associated climate variables. A(max), g(s), g(m) and more marginally, photosynthetic nitrogen-use efficiency (PNUE) were positively associated with the mean July temperature of the SO, while water use efficiency (WUE) was negatively associated. Maximum rates of carboxylation (V(cmax)), maximum rates of electron transport (J(max)), SLA, N(mass), NSC and R/S showed no pattern. Our results did not demonstrate a higher Amax for northern seed orchards, although this has been previously hypothesized as an adaptation mechanism for maintaining carbon uptake in northern regions. We suggest that gs, gm, WUE and PNUE are the functional traits most associated with fine-scale geographic clines and with the degree of local adaptation of white spruce populations to their biophysical environments. These geographic patterns may reflect in situ adaptive genetic differences in photosynthetic efficiency along the cline.

The retention of overstory trees in a shelterwood-with-reserves regeneration method provides structural legacies, but at an unknown cost to white pine regeneration growth. Height, breast height diameter, and basal diameter growth responses of 12–15 year-old naturally regenerated eastern white pine (Pinus strobus L.) to partial overstory removal and pathological pruning (i.e., the removal of lower branches that are most susceptible to blister rust infection) were monitored over four growing seasons in a 110-year-old red pine (Pinus resinosa Ait.) - white pine stand. A two-cut shelterwood-with-reserves system with an average basal area of 23 m2 ha−1 initiated white pine regeneration in 1983. Partial overstory removal in the winter of 1998/99 followed by the July 4th 1999 blowdown event retained an average basal area of 4.5 m2 ha−1 (± 2.3). Five-year white pine seedling growth responses were independent of the level of overstory retention and pruning. Damage from white pine weevil and white pine blister rust were minimal. Residual red and white pines also increased radial growth in response to partial overstory removal. We conclude that a two-cut shelterwood-with-reserves system enhances the structural heterogeneity of the stand without reducing short-term growth of the regeneration. Given low blister rust infection rates, pruning 12–15 year-old white pine under a partial canopy may be unnecessary.

White pine blister rust (caused by Cronartium ribicola J.C. Fisch.) is a primary cause of poor survival and growth of eastern white pine (Pinus strobus L.) and has contributed to the species’ decline across its range. Genetic resistance to C. ribicola is generally weak in eastern white pine, possibly owing to the absence of meaningful resistance alleles. Integrating major resistance genes from Eurasian 5-needle pine species to P. strobus has been demonstrated to be effective through traditional plant breeding approaches. This paper provides a review of progress after more than half a century of breeding and testing in Ontario. Key words: Pinus strobus, white pine blister rust, genetic resistance, interspecific hybridization

The ecophysiological traits of acacia and eucalypt are important in assessing their suitability for afforestation. We measured the gas-exchange rate, the leaf dry mass per area (LMA) and the leaf nitrogen content of two acacia and four eucalypt species. Relative to the eucalypts, the acacias had lower leaf net photosynthetic rate (PN), lower photosynthetic nitrogen-use efficiency (PNUE), higher water-use efficiency (WUE), higher LMA and higher leaf nitrogen per unit area (Narea). No clear differences were observed within or between genera in the maximum rate of carboxylation (Vcmax) or the maximum rate of electron transport (Jmax), although these parameters tended to be higher in eucalypts. PNUE and LMA were negatively correlated. We conclude that acacias with higher LMA do not allocate nitrogen efficiently to photosynthetic system, explaining why their PN and PNUE were lower than in eucalypts.

Genetic resistance to white pine blister rust, restoration options, and potential use of biotechnology

Dahurian larch (Larix gmelinii) is the dominant tree species in boreal forests, and its photosynthetic response to climate warming is important in modeling and predicting carbon cycling for boreal forest ecosystems. In 1983, seedlings of L. gmelinii from 11 provenances were transplanted into two common gardens with different climate conditions (control and warming climate). Forty years after the transplant, we investigated the response of leaf photosynthetic capacity to climate warming and its variation among provenances. The warming treatment significantly increased the maximum net photosynthetic rate (Pmax-a), photosynthetic nitrogen use efficiency (PNUE), maximum carboxylation rate (Vcmax), maximum electron transport rate (Jmax), triose phosphate utilization rate (TPU), mesophyll conductance (gm), leaf nitrogen content (Narea), and chlorophyll content (Chlm). Pmax-a was significantly positively associated with Vcmax, Jmax, TPU, gm, and Narea, and the slope of the linear regression between Pmax-a and Vcmax, Jmax, and TPU was greater in the warming treatment. The responses of Pmax-a, PNUE, Vcmax, Jmax, TPU, Narea, and Chlm to warming differed among provenances. As the aridity index of the original site increased, the magnitude of the warming treatment’s effect on Pmax-a, Vcmax, Jmax, and TPU represented a varying form of a bell-shaped curve. Overall, the warming treatment improved the photosynthetic capacity of L. gmelinii, but the extent of the improvement varied among provenances. These findings provide insights into the mechanisms underlying the responses of L. gmelinii to climate warming.

巴郎山异型柳叶片功能性状及性状间关系对海拔的响应

White pine blister rust (WPBR) (Cronartium ribicola J. C. Fischer) has been present in Vermont and other northeastern states since the early 1900s. The fungus is commonly observed on currants and gooseberries (Ribes L.) every year, but incidence varies on eastern white pine (Pinus strobus L.). Our general impression has been that Vermont has had a relatively low level of infection on eastern white pines; however, we recently found rust incidence in Christmas tree plantings in northern Vermont to range from 10 to 42% (average 20%) based on 721 trees surveyed. Also, in pole-sized stands in southern Vermont, incidence ranged from 12 to 46% (average 32%) and 76% of these trees had main stem infections. In the southern survey, 98% of wild ribes plants had varied amounts of both urediniospores and teliospores. These preliminary survey data suggest that incidence of WPBR may be more significant than previously thought and therefore, additional survey work is needed. We screened cultivars of Ribes for susceptibility to WPBR. Eighteen cultivars were inoculated in the field with a mass collection of aeciospores of C. ribicola. The percentages of leaf area infected ranged from 0 to 49 for the urediniospore stage and from 0 to 55 for teliospores. The gooseberry (Ribes uva-crispa L.) `Welcome' had the highest percentage of leaf area with urediniospores, while black currants (R. nigrum L.) `Coronet,' `Consort,' and `Crusader' had no visible infection. Presently, Vermont has no WPBR regulations. However, previous federal laws did restrict black currant cultivation. Little is known about the genetic diversity of WPBR or its potential for change. Caution must be used when considering any cultivation of Ribes for the purpose of producing fruit because our valued white pine resources could be negatively impacted.

Between 1936 and 1996, the Forest Insect and Disease Survey (FIDS) of the Canadian Forest Service of Natural Resources Canada surveyed eastern white pine (Pinus strobus L.) throughout Atlantic Canada. During those years, FIDS reported its insect and disease findings in a wide variety of regional and national reports and in the scientific literature. The National Forest Health Database contains these electronic records and indicates the distribution and relative importance of forest diseases and fungi for many tree species in Atlantic Canada. This paper is a frequency analysis of the fungal diseases recorded from the Atlantic provinces in the National Forest Health Database and reported in the various Maritime, Newfoundland and national FIDS reports. The significant eastern white pine diseases (e.g., white pine blister rust – Cronartium ribicola J.C. Fisch.) that are established in Atlantic Canada as well as other diseases that are found elsewhere in Canada, but not yet in the Atlantic provinces are discussed. Occurrence data for 40 of the less frequently collected fungal species are presented in a summary table. Key words: white pine blister rust, Cronartium ribicola, eastern white pine, Pinus strobus, Scleroderris canker, Gremmeniella abietina, Annosus root rot, Heterobasidion annosum, white pine root decline, Leptographium procerum, needle cast, Lophodermium pinastri, brown felt fungus, Septobasidium pinicola, Atlantic Canada, forest disease

The relationship of stand structural features with understory light levels, estimated by gap light index (GLI), was investigated in 22 second-growth eastern white (Pinus strobus L.) and red pine (Pinus resinosa Ait.)-dominated stands in central Ontario that encompassed a broad range in density and basal area. Simple, empirical light models were developed to quantify the influence of several stand structural variables on canopy transmittance as estimated by GLI. Models were also derived to facilitate the operational identification of residual basal area, density, and percent canopy closure associated with target understory light levels that optimize the growth of white pine regeneration and its protection from weevil and blister rust when using the uniform shelterwood silvicultural system. Regression models indicated significant negative, nonlinear relationships of GLI with density, basal area, a stand density index, total crown area, and foliar biomass, while GLI was linearly related to percent canopy closure. Application of these models to identify density, basal area, and canopy closure values associated with target light levels for the regeneration and removal cuts of uniform shelterwoods demonstrates the use of this information to help guide management of white pine–red pine forests.