Pine Hybrids Research Articles

Accounting for competition in multi-environment tree genetic evaluations: a case study with hybrid pines

Key message A novel multi-environment competition individual-tree mixed model resulted in better fit, and greater individual narrow- and broad-sense heritabilities than the model without competition, notably for traits showing competition. In multi-environment tests, the proposed model would allow tree breeders to select genotypes with the best performance in both additive direct and competition breeding values, increasing forest productivity. ContextGenetic merit of trees is known to be affected and interact with local competition effects as well as changes across environmental conditions. Recent studies showed that competition genetic effects can affect the genetic variance and bias the tree breeding values, and its covariance with direct breeding values has been variable across traits.AimsThe present paper extends a mixed-model methodology to the problem of accounting for competition in a multi-environment set of forest genetic trials and exploring its impact on genetic variances as well as the multi-environment genetic correlation.MethodsThe proposed model is illustrated using data from two full-sib trials of Pinus elliottii var. elliottii × Pinus caribaea var. hondurensis F1. Dispersion parameters and (co)variance of total breeding values were estimated for diameter at breast height, total tree height, and stem straightness at age 10.ResultsFor traits showing competition effects (diameter at breast height and total tree height), the proposed multi-environment competition model gave better fit than the simpler model. Accounting for competition increased the direct additive variance, reduced the residual variances, and did not change significantly the across-site additive genetic correlation. However, for diameter at breast height, top 5% best genetic rankings showed differences.ConclusionWhen traits are strongly affected by inter-tree competition, the use of the proposed model in multi-environment analyses can efficiently identify the phenomenon with general benefits in the fitting of genetic components and open the door to select on the basis of competitiveness.

Hybrid Pine (Pinus attenuata × Pinus radiata) Somatic Embryogenesis: What Do You Prefer, Mother or Nurse?

Development of hybrid pines of Pinus radiata D. Don for commercial forestry presents an opportunity to diversify the current resource of plant material. Climate change and different land uses pose challenges, making alternative species necessary to guarantee wood and non-wood products in the future. Pinus radiata var. cedrosensis × Pinus attenuata hybrid possesses different attributes, such as tolerance to drought conditions, better growth and resistance to snow damage at higher altitudes, and more importantly, different wood quality characteristics. Embryogenic cell lines were successfully initiated reciprocal hybrids using as initial explants megagametophytes, excised zygotic embryos and excised zygotic embryos plus nurse culture. However, the questions raised were: does the initiation environment affect the conversion to somatic plantlets months later? Does the mother tree or the cross have an effect on the conversion to somatic plantlets? In the present work we analysed the maturation rate, number of somatic embryos, germination rate, and the ex-vitro growth in cell lines derived from different initiation treatments, mother tree species, and crosses. Differences were not observed for in vitro parameters such as maturation and germination. However, significant differences were observed due to the mother tree species in relation with the ex-vitro growth rates observed, being higher those in which P. radiata acted as a mother. Moreover, embryogenic cell lines from these hybrids were stored at −80 °C and regenerated after one and five years.

Growth and modulus of elasticity of pine species and hybrids three years after planting in South Africa

Growth data and modulus of elasticity (MOE) of 11 different pine species and hybrids were examined at six sites in three regions in South Africa. Growth traits and three MOE variables were measured at three years of age in order to evaluate whether other potential pine species were more suitable than the current commercial species. There were strong observed species differences for all three MOE variables both within and across the four sites measured for wood properties, with across-site MOE ranging from 3.03 to 6.40 GPa. Green density varied among species, and an assumed constant green density of 1 000 kg m–3 underestimated MOE for species with a very high green density; similarly, for species with a very low green density, MOE was overestimated. Although survival was poor at several sites, the data shows that there are alternative pine species that exhibit comparable growth rates to the current commercial species. For estimating MOE, it is concluded that assuming a constant green density generally does not affect the species ranking, but if the aim is to find the ‘true’ MOE, sampling in the field to determine the appropriate green density is needed.

Influence of wood’s anatomical and resin traits on the radial permeability of the hybrid pine (Pinus elliottii × Pinus caribaea) wood in Australia

Wood permeability has a major effect on industrial wood processing and utilization. Wood anatomy and resin influence the permeability of wood. Understanding and manipulating these influences is important to optimize the manufacture and use of forest products. This study investigated the relationships between wood anatomical traits, radial permeability, and resin content of samples collected from 19-year-old hybrid pines (Pinus elliottii var. elliottii × Pinus caribaea var. hondurensis) from Queensland, Australia. The earlywood tracheid tangential lumen diameter and axial resin canal diameter were statistically positively correlated with radial permeability. The heartwood proportion and the frequency of axial resin canals were statistically negatively correlated with radial permeability and positively correlated with resin content. The axial resin canal diameter, sapwood proportion, latewood content, ray frequency, and earlywood tracheid lumen diameter increased from pith to bark, whereas the axial resin canal frequency decreased. Resin was found distributed throughout the wood microstructure, from pith to bark in many samples, and in both heartwood and sapwood. However, there was a much greater quantity of resin in heartwood and wood from the middle (inner radius) of the tree, with widespread occurrence of resin impregnation in the axial tracheids.

Water absorption and its effect on mechanical properties of hybrid wood particulates composites

The hydrophilicity/hygroscopicity of wood particle reinforced epoxy composites offer the degradation in its mechanical properties, and also restricts these composites for outdoor or moisture changing environmental applications. The present work aims at experimental investigations of water uptake behaviour of hybrid softwood/hardwood particle reinforced epoxy composite and its effect on the mechanical properties. The hybrid pinus (softwood or SWP) and shorea robusta (Hardwood or HWP) epoxy composites are prepared keeping constant 25 wt% as total amount of reinforcement with varying ratio of wood particulates. The water absorption analysis includes determination of percentage water-soaked; sorption, diffusion and permeability coefficients of hybrid composites. The tensile, flexural and impact tests are conducted on water-soaked samples to study the effects of water absorption. The SEM morphology of water-soaked samples under different mode of loadings is also presented. The water resistance capacity and lowering in the mechanical degradation by water absorption of wood composites are found to enhance by hybridization of pinus and shorea robusta wood particulates.

Spatial and genetic structure of the lodgepole × jack pine hybrid zone

In north-central Alberta, lodgepole pine (Pinus contorta Dougl. ex Loud. var. latifolia) and jack pine (Pinus banksiana Lamb.) form a mosaic hybrid zone, the spatial extent of which remains poorly defined. We sought to refine the genetic and geographic distribution of this hybrid zone in western North America to provide information important in predicting future risk of mountain pine beetle (Dendroctonus ponderosae Hopkins) outbreaks. We used 29 single nucleotide polymorphism (SNP) markers to discriminate lodgepole pine, jack pine, and their hybrids. We compared and contrasted spatial patterns of hybridization in northern and southern forest zones based on the colonization history of the two species. We found that patterns of introgression were more similar between the zones than expected by chance, but there were significant differences between these regions at specific loci. Using logistic regression, we created a robust predictive model to distinguish among lodgepole pine, jack pine, and their hybrids using a combination of geographic and environmental predictors. Using model selection based on Akaike information criterion, we found that location, elevation, and moisture are important predictors for species class. Quantification of the genetic differences between these two regions, combined with an accurate model for predicting the spatial distribution of lodgepole pine, jack pine, and their hybrids, provides essential information for continued effective management of forest resources.

Radial permeability of the hybrid pine (Pinus elliottii × Pinus caribaea) in Australia

The radial permeability (gas and liquid) of the hybrid pine (Pinus elliottii var. elliottii [PEE] × Pinus caribaea var. hondurensis [PCH]) was investigated for wood samples collected from 30 trees that were 19 years of age and represented various genotypes and stocking rates. The PEE × PCH hybrid is now a very important resource for the Australian forestry industry, producing logs used to manufacture a diverse array of wood products. The permeability of wood influences many important wood properties and industrial processes. For all data combined from all radial sampling positions, there was no significant effect of genotype and stocking rate on radial permeability. Both gas and liquid permeability increased from pith to bark positions within the tree. Conversely, resin content decreased from pith to bark positions. Gas and liquid permeability were significantly positively correlated, and a highly significant negative relationship was also found between permeability (gas and liquid) and resin content.

PRODUCTIVIDAD DE UN HARVESTER EN RALEOS DE PLANTACIONES DE PINOS EN EL NORESTE ARGENTINO

Se analizó la productividad de segundos y terceros raleos en plantaciones de Pinus taeda y Pinus elliottii var. elliottii x Pinus caribaea var. hondurensis realizados con harvesters de ruedas en el Noreste Argentino. Los árboles cosechados en los segundos raleos presentaron un volumen medio de 0,43 m³ para Pinus taeda de 12 años y 0,36 m³ para pino hibrido de 10 años, mientras que en los terceros raleos este valor fue de 0,71 m³ para Pinus taeda de 13 años y 0,75 m³ para pino hibrido de 15 años respectivamente. Se desarrollaron modelos de tiempos parciales para cada una de las actividades que componen el ciclo operacional y se determinó la influencia del tipo de raleo, especie cosechada, número de productos elaborados, volumen de los árboles y forma de volteo, sobre el tiempo insumido por cada actividad. Los modelos ajustados fueron integrados en un modelo de productividad efectiva consiguiéndose un coeficiente de determinación ajustado R2 Aj de 0,61. El volumen de los árboles resultó significativo para explicar la duración de todas las actividades evaluadas, siendo especialmente determinante en el volteo de los árboles, su desrame y trozado. El tipo de raleo afectó al tiempo de ubicación, mientras que la especie afectó al tiempo de desrame y trozado. La elaboración de hasta tres productos diferentes requirió un mayor tiempo destinado al desrame y trozado. Ocurrió un aumento de la cantidad de productos cuando se realizaron terceros raleos sobre pino hibrido, respecto Pinus taeda.

Alternative pine hybrids and species to Pinus patula and P. radiata in South Africa and Swaziland

Through the collaborative efforts of companies affiliated with the International Program for Tree Improvement and Conservation (Camcore), a number of pine hybrids have been produced over the last decade. Many of these have been planted in trials across southern Africa that broadly represent winter and summer rainfall areas, with the latter ranging from warm to cold temperate sites. The five-year survival and growth of the hybrids and other pines in 12 of these trials were compared with Pinus radiata in the winter rainfall, and P. patula in the summer rainfall, regions where these species have been planted extensively. Except for the highest altitude site, where freezing conditions are common, the survival of most hybrids and tropical pines was better than P. patula or P. radiata. This was, in part, attributed to their improved tolerance to the pitch canker fungus, Fusarium circinatum, which was present in the nursery at the time of planting. In the winter rainfall area, the P. elliottii × P. caribaea hybrid, P. maximinoi and, surprisingly, the P. patula hybrids performed well. In the summer rainfall regions, hybrids with tropical parents such as P. caribaea, P. oocarpa and P. tecunumanii were more productive in the subtropical/warm temperate zone and, with increasing elevation, those hybrids crossed with P. patula performed relatively better. The P. patula × P. tecunumanii hybrid, particularly when crossed with low-elevation P. tecunumanii, performed exceptionally across most sites.

Root growth of somatic plants of hybrid Pinus strobus (L.) and P. wallichiana (A. B. Jacks.) is affected by the nitrogen composition of the somatic embryo germination medium

This paper describes improvement in root growth of hybrid white pine somatic plants on a somatic embryo germination medium containing solely organic nitrogen sources. Mature somatic embryos of F2 hybrid Pinus strobus × Pinus wallichiana backcrossed with P. strobus converted to plants but survival of the somatic plants was not satisfactory prompting the present study on somatic seedling root growth on germination media varying in nitrogen (N) composition. The media were modifications of Litvay’s (Litvay et al. in Plant Cell Rep 4:325–328, 1985) which included two main groups: G1, G2, G3, G4 all contained inorganic N with or without glutamine (Gln) or casein hydrolysate (CH) and G5, G6, G7 contained solely glutamine and/or CH. In addition, G8 was half-strength G1 (with organic N) and G9 was half-strength CD (Campbell and Durzan in Can J Bot 53:1652–1657, 1975) without organic N. The roots of plants growing on media containing solely organic N grew about 2.55 times longer than on those containing solely inorganic N or both inorganic and organic N. The longest roots grew on G7 supplemented with CH and on G5 with both CH and Gln. Microarray analysis of somatic plants germinated on G1 versus G7 revealed that depending on the N source the somatic plants displayed changes in the transcriptome resulting in the differential expression of a range of genes involved in essential processes for plant growth and development. Roots grown in the absence of inorganic N were capable of rapid uptake of labelled inorganic 15N during the 2 h incubation in the nutrient solution. The somatic plants from G5 medium acclimatized at the rate twice as high as those from G1 (with both inorganic and organic N) and G2 (solely inorganic N) under standard fertilization regime.

Comparison of biomass partitioning and transpiration for water-stressed shortleaf, loblolly, and shortleaf × loblolly pine hybrid seedlings

Hybridization between shortleaf pine (Pinus echinata Mill.) and loblolly pine (Pinus taeda L.) has dramatically increased and may threaten the genetic integrity of shortleaf pine. Shortleaf pine is presumed to be more drought tolerant than loblolly pine, but the drought hardiness of the hybrid pine is not known. We determined biomass partitioning in response to water stress and measured whole-plant transpiration of shortleaf, loblolly, and hybrid pine seedlings. Water stress decreased total seedling biomass, increased biomass partitioning to foliage, and decreased biomass partitioning to coarse roots. Shortleaf pine seedlings partitioned more biomass to coarse roots than loblolly pine, and hybrid pine was intermediate between the parent species. We found no differences in the level of soil moisture at which seedlings of different species began to limit transpiration. Our results suggest that the transpiration response of shortleaf pine and hybrid pine is similar to that of loblolly pine when exposed to water stress. However, greater partitioning to coarse root may allow shortleaf and hybrid pines to better withstand drought due to greater potential belowground carbohydrate supply.

Somatic embryogenesis of hybrid Pinus elliottii var. elliottii × P. caribaea var. hondurensis and ploidy assessment of somatic plants

A protocol is described for somatic embryogenesis (SE) Pinus elliottii × P. caribaea, an interspecific pine hybrid of major economic importance. Different embryogenesis conditions were tested, from time of initiation to plant regeneration. Immature megagametophytes containing zygotic embryos of five open pollinated (OP) mother trees were used for SE initiation. An established rate of 10.2% was achieved for explants inoculated on modified Litvay’s medium (mLV), supplemented with BAP (4.5 µM) and 2,4-D (9 µM). Initiation of SE was influenced by the mother-tree genotype however, modification of culture conditions enabled establishment of embryogenic cell lines (ECLs) from all OP seed families. Fifty-two percent of somatic embryos developed to the cotyledonary stage on mLV, supplemented with 40 µM ABA and 6% w/v sucrose. Cotyledonary stage somatic embryos converted to plants at 45–86%. Four months after acclimatization in a greenhouse, plant survival rates ranged between 78 and 94%. Flow cytometry analysis of ploidy, did not show any variation in ECLs and somatic seedlings.

Tree breeding model to assess financial performance of pine hybrids and pure species: deterministic and stochastic approaches for South Africa

Financial performance of the P. patula × P. tecunumanii, P. greggii × P. tecunumanii, P. taeda × P. tecunumanii hybrids and their parental species was studied for South Africa. A model was developed for use in determining the profitability of a tree-breeding program (TBP) with pine hybrids in commercial plantations. Growth measurement data were collected in four, 12-year-old genetic trials on Mondi and Sappi land holdings in South Africa. Growth models developed for P. patula and P. taeda in South Africa were used to infer models for the other taxa and to calculate the optimal financial rotation age at discount rates of 6 and 8%. Financial data on pine plantations were collected from different sources in South Africa. Optimal rotation lengths in this study were found to be between 12 and 16 years for pulpwood and 17 years for sawtimber. The model output shows the net present value (NPV), the internal rate of return, and the minimum area that a tree grower has to plant every year in order to justify the investment in a TBP. A stochastic approach with Monte Carlo simulation showed that the sensitivity of NPV to uncertainty in the wood price was greater than that for the planting, harvesting, and transport costs.

Plant regeneration from ploidy-stable cryopreserved embryogenic lines of the hybrid Pinus elliottii x P. caribaea

Clonal breeding programs of the highly important interspecific hybrid Pinus elliottii var. elliottii and Pinus caribaea var. hondurensis require the establishment of robust cryopreservation protocols, with no genetic variability. Embryonal masses of this hybrid were successfully cryopreserved by a fast slow-freezing method. The protocol was optimized by testing the effects of dimethyl sulfoxide (DMSO) based cryoprotectant solutions, sugar cryoprotectants (e.g. sucrose or maltose, 0.4M) and different times of pretreatments and pre-cooling storage. The addition of DMSO in a mixture of polyethylene glycol (PEG) 4000 and sucrose (PSD solution), instead of DMSO alone, was beneficial for recovery of cryopreserved cultures. This parameter, together with the time of pre-cooling storage (before plunging in liquid nitrogen), were the factors that most influenced the survival and regrowth rates of embryonal masses. A pretreatment combination of sucrose (0.4M) and 5% PSD followed by a pre-cooling storage of 24h allowed the cryopreservation and regrowth of embryogenic cell lines without major genetic variations (DNA-ploidy) or loss of embryogenic potential. Eight of the nine tested embryogenic cell lines survived to the cryopreservation procedures, however the genotype and treatment conditions clearly influenced the response. Somatic embryos maturation and conversion from recovered embryonal masses (EMs) took place according to our standard somatic embryogenesis protocol for Pinus, using modified Litvai (mLV) medium. This is the first report for this hybrid, and the proposed protocol is fast, robust, providing high rates of recovery and working with several genotypes. This protocol’s suitability for industrial breeding programmes was also confirmed by allowing the regeneration of plants with no apparent variability from cryopreserved embryonal masses.

Occurrence of Shortleaf × Loblolly Pine Hybrids in Shortleaf Pine Orchards: Implications for Ecosystem Restoration

Occurrence of Shortleaf × Loblolly Pine Hybrids in Shortleaf Pine Orchards: Implications for Ecosystem Restoration

Nurse tissue for embryo rescue: testing new conifer somatic embryogenesis methods in a F1 hybrid pine

Key message This is the first report of (1) somatic embryogenesis in the hybrids ofPinus attenuatawithPinus radiatavar.cedrosensisand (2) use ofPinus radiatasomatic embryogenic tissue as nurse tissue to facilitate initiation from immature hybrid pine zygotic embryos.

Post-fire resprouting of shortleaf pine is facilitated by a morphological trait but fire eliminates shortleaf × loblolly pine hybrid seedlings

Concurrent with fire exclusion, shortleaf pine×loblolly pine hybrids have increased throughout the southeastern USA and may threaten the genetic integrity of shortleaf pine. Historically, fire favored shortleaf pine over other southern pine species, especially loblolly pine, with which it shares a broad sympatric natural range. Shortleaf pine seedlings have a morphological adaptation (basal crook) that lowers dormant buds to the soil surface where they are presumably protected from fire to facilitate resprouting after topkill. To evaluate this presumption, we tested (1) the functional role of the basal crook in protecting dormant buds by measuring resprouting after exposing the lower stem of shortleaf pine to fire and protecting from fire the lower stem (and dormant buds) of loblolly pine (which lacks a basal crook) and (2) the occurrence and importance of the basal crook morphological adaptation in F1 shortleaf×loblolly pine seedlings by comparing morphology and post-fire resprouting of the hybrids to both parents. Fire exposure of shortleaf pine seedling dormant buds caused seedling mortality, while protecting loblolly pine dormant buds facilitated resprouting. Hybrid pines have basal crooks intermediate to the strong crook of shortleaf pine and loblolly pine’s non-crooked stem. Fire top-killed loblolly pine and shortleaf×loblolly pine seedlings, and they did not resprout, while 57% of shortleaf pine resprouted after topkill during two dormant season and one growing season burns. This highly significant difference shows that the basal crook is important for shortleaf pine resprouting after topkill by fire. Fire is an important tool to reduce shortleaf×loblolly pine hybrids, and to provide a competitive advantage to shortleaf pine relative to loblolly pine, for ecosystem restoration and maintaining the genetic integrity of shortleaf pine.

Performance of Sirex noctilio’s biocontrol agent Deladenus siricidicola, in known and predicted hosts

Survival of the free-living mycetophagous form of Deladenus siricidicola, the major biological control agent of Sirex woodwasp, Sirex noctilio, was tested in known (Pinus taeda) and predicted novel (P. elliottii subsp. elliottii×P. caribaea var. hondurensis) hybrid host taxa. Trials were established in the field to simulate nematode dispersal both naturally by infected wasps and following commercial inoculation, as well as in the laboratory under controlled conditions. Nematodes showed reduced survival in hybrid pine compared with P. taeda for all tree-associated treatments, but performed equivalently in petri-dish bioassays containing substrate of each taxon. Growth of Amylostereum areolatum, the food source of D. siricidicola was lower on plates containing ground hybrid substrate than on plates containing ground P. taeda. Some physical differences were found between taxa, including differences in bordered pit diameters, tracheid widths, and basic density, but these did not consistently explain reduced performance. More plant secondary compounds (predominantly oleoresins) were present in hybrid taxa than in P. taeda, and in standing trees compared with felled trees. Our results suggested that D. siricidicola may not be as effective in hybrid pine taxa for the biological control of S. noctilio as it is in its current known host taxa, possibly because of reduced growth of its food source, A. areolatum in hybrid pine.

The Effect of Water Limitation on Volatile Emission, Tree Defense Response, and Brood Success of Dendroctonus ponderosae in Two Pine Hosts, Lodgepole, and Jack Pine

The mountain pine beetle (MPB; Dendroctonus ponderosae) has recently expanded its range from lodgepole pine forest into the lodgepole × jack pine hybrid zone in central Alberta, within which it has attacked pure jack pine. This study tested the effects of water limitation on tree defense response of mature lodgepole and jack pine (Pinus contorta and Pinus banksiana) trees in the field. Tree defense response was initiated by inoculation of trees with the MPB-associated fungus Grosmannia clavigera and measured through monoterpene emission from tree boles and concentration of defensive compounds in phloem, needles, and necrotic tissues. Lodgepole pine generally emitted higher amounts of monoterpenes than jack pine; particularly from fungal-inoculated trees. Compared to non-inoculated trees, fungal inoculation increased monoterpene emission in both species, whereas water treatment had no effect on monoterpene emission. The phloem of both pine species contains (-)-α-pinene, the precursor of the beetle’s aggregation pheromone, however lodgepole pine contains two times as much as jack pine. The concentration of defensive compounds was 70-fold greater in the lesion tissue in jack pine, but only 10-fold in lodgepole pine compared to healthy phloem tissue in each species, respectively. Water-deficit treatment inhibited an increase of L-limonene as response to fungal inoculation in lodgepole pine phloem. The amount of myrcene in jack pine phloem was higher in water-deficit trees compared to ambient trees. Beetles reared in jack pine were not affected by either water or biological treatment, whereas beetles reared in lodgepole pine benefited from fungal inoculation by producing larger and heavier female offspring. Female beetles that emerged from jack pine bolts contained more fat than those that emerged from lodgepole pine, even though lodgepole pine phloem had a higher nitrogen content than jack pine phloem. These results suggest that jack pine chemistry is suitable for MPB pheromone production and aggregation on the host tree.

Genetic parameters in subtropical pine F1 hybrids: heritabilities, between-trait correlations and genotype-by-environment interactions

Growth and stem straightness traits of 29 Pinus caribaea var. hondurensis × Pinus tecunumanii (PCH × PTEC) and 26 P. caribaea var. hondurensis × Pinus oocarpa (PCH × POOC) hybrid pair-crosses plus a total of 16 intraspecific families were assessed at ages 5, 8 and 15 years from planting at two sites. The PCH × PTEC hybrid was the most productive, yielding 37 % more than a Pinus elliottii local control and was 21 % superior to either parental species in DBH growth. PCH × POOC hybrid was, on average, 16 % superior to either parental species for DBH. Narrow-sense heritability estimates were low to moderate for growth traits (average of 0.27) and stem straightness (0.16). The estimated additive genetic correlations between growth traits and ages within traits were high (>0.8) and positive, providing confidence in early selection based on diameter at breast height. The high proportion of estimated additive genetic variance compared to dominance variance in the F1 pine hybrids suggests that breeding strategies that maximize the use of additive genetic variance may be effective. The ranking of the 11 PCH parents based on general hybridizing ability predictions (estimated breeding values as hybrids) was somewhat inconsistent between PTEC and POOC hybrid crosses for all traits (r 9 d.f. = 0.38–0.45; p ∼0.15–0.25). There was no evidence of practically important G × E interaction for the hybrids except for PCH × PTEC height growth. This study suggests that a single, multi-hybrid breeding population seems appropriate in Zimbabwe if the trial sites are representative of the planting target zone.