Quantitative trait locus (QTL) analysis of growth and vegetative propagation traits in <Emphasis Type="Italic">Eucalyptus nitens</Emphasis> full-sib families

Tree growth and vegetative propagation are complex but important traits under selection in many tree improvement programmes. To understand the genetic control of these traits, we conducted a quantitative trait locus (QTL) study in three full-sib families of Eucalyptus nitens growing at two different sites. One family growing at Ridgley, Tasmania had 300 progeny and two clonally replicated families growing at Mt. Gambier, South Australia had 327 and 210 progeny. Tree growth was measured over several years at both sites and percentages of roots produced by either stem cuttings or tissue culture were assessed in the two Mt. Gambier families. Linkage analysis of growth traits revealed several QTLs for later year traits but few for early year traits, reflecting temporal differences in the heritabilities of these traits. Two growth QTL positions, one on LG8 and another on LG11 were common between the Ridgley and Mt. Gambier families. Four QTLs were observed for each of the two vegetative propagation methods. Two QTLs for vegetative propagation on LG7 and LG11 were validated in the second family at Mt. Gambier. These results suggest that growth and vegetative propagation traits are controlled by several small effect loci. The QTLs identified in this study are useful starting points for identifying candidate genes using the Eucalyptus grandis genome sequence.     

Quantitative genetic architecture of adaptive phenology traits in the deciduous tree,Populus trichocarpa (Torr. and Gray)

In a warming climate, the ability to accurately predict and track shifting environmental conditions will be fundamental for plant survival. Environmental cues define the transitions between growth and dormancy as plants synchronise development with favourable environmental conditions, however these cues are predicted to change under future climate projections which may have profound impacts on tree survival and growth. Here, we use a quantitative genetic approach to estimate the genetic basis of spring and autumn phenology in Populus trichocarpa to determine this species capacity for climate adaptation. We measured bud burst, leaf coloration, and leaf senescence traits across two years (2017–2018) and combine these observations with measures of lifetime growth to determine how genetic correlations between phenology and growth may facilitate or constrain adaptation. Timing of transitions differed between years, although we found strong cross year genetic correlations in all traits, suggesting that genotypes respond in consistent ways to seasonal cues. Spring and autumn phenology were correlated with lifetime growth, where genotypes that burst leaves early and shed them late had the highest lifetime growth. We also identified substantial heritable variation in the timing of all phenological transitions (h² = 0.5–0.8) and in lifetime growth (h² = 0.8). The combination of additive variation and favourable genetic correlations in phenology traits suggests that populations of cultivated varieties of P. Trichocarpa may have the capability to adapt their phenology to climatic changes without negative impacts on growth.Subject terms: Plant breeding, Forest ecology, Evolutionary genetics     

Identification of QTLs affecting adaptive traits in Castanea sativa Mill

A QTL analysis for three different adaptive traits was performed in an F₁ progeny of Castanea sativa Mill. The female and male parents originated from two Turkish chestnut populations adapted to a drought and humid environment, respectively. QTLs for bud flush, growth and carbon isotope discrimination were detected over a 3‐year period. Bud set was also recorded in the last year of measurement. Thirty‐five individual QTLs were detected for phenology, 28 for growth and 17 for carbon isotope discrimination, most of them explaining a low to moderate proportion of the total phenotypic variance. QTLs were distributed throughout the whole genome. Temporally stable QTLs were identified for all the traits analysed, with phenology showing the higher proportion of stable QTLs. Interesting phenotypic correlations and co‐localizations among QTLs for different adaptive traits were observed, allowing the formulation of an hypothesis about the genetic adaptation of the female parent to drought.     

Effects of propagule type on genetic parameters of wood density and growth in a loblolly pine progeny test at ages 10 and 11?years

Nine full-sib families of loblolly pine (Pinus taeda L.) were produced by a 3 × 3 factorial mating design. Rooted cuttings and seedlings of full-sib families were tested together in two field locations. Twelve-millimeter wood increment cores were collected from 10- and 11-year-old test trees. On each of the two sites, there were six blocks and a split-plot design, with propagule type as the whole plot and family as the sub-plot. In addition to the collection of wood samples, height and diameter of 1,600 trees were measured. No significant differences were found between cuttings and seedlings for wood density and growth traits. Significant family variation was found for growth and wood density. Genetic parameters estimated for wood density and growth traits using seedlings and rooted cuttings showed that individual-tree and family heritability estimates from rooted cuttings were similar to or higher than those from seedlings for all traits. Half-sib breeding values for parents were highly correlated based on seedling and rooted cutting estimates for height (0.95) and wood density (0.99) but not for diameter (0.56), which suggests that wood density and height breeding value estimates from rooted cuttings in clonal progeny tests can be estimated by traditional seedling tests, but not for tree diameter.     

Genetic improvement of the chemical composition of Scots pine (Pinus sylvestris L.) juvenile wood for bioenergy production

Chemical composition is one of the key characteristics that determines wood quality and in turn its suitability for different end products and applications. The inclusion of chemical compositional traits in forest tree improvement requires high‐throughput techniques capable of rapid, non‐destructive and cost‐efficient assessment of large‐scale breeding experiments. We tested whether Fourier‐transform infrared (FTIR) spectroscopy, coupled with partial least squares regression, could serve as an alternative to traditional wet chemistry protocols for the determination of the chemical composition of juvenile wood in Scots pine for tree improvement purposes. FTIR spectra were acquired for 1,245 trees selected in two Scots pine (Pinus sylvestris L.) full‐sib progeny tests located in northern Sweden. Predictive models were developed using 70 reference samples with known chemical composition (the proportion of lignin, carbohydrates [cellulose, hemicelluloses and their structural monosaccharides glucose, mannose, xylose, galactose, and arabinose] and extractives). Individual‐tree narrow‐sense heritabilities and additive genetic correlations were estimated for all chemical traits as well as for growth (height and stem diameter) and wood quality traits (density and stiffness). Genetic control of the chemical traits was mostly moderate. Of the major chemical components, highest heritabilities were observed for hemicelluloses (0.43–0.47), intermediate for lignin and extractives (0.30–0.39), and lowest for cellulose (0.20–0.25). Additive genetic correlations among chemical traits were, except for extractives, positive while those between chemical and wood quality traits were negative. In both groups (chemical and wood quality traits), correlations with extractives exhibited opposite signs. Correlations of chemical traits with growth traits were near zero. The best strategy for genetic improvement of Scots pine juvenile wood for bioenergy production is to decrease and stabilize the content of extractives among trees and then focus on increasing the cellulose:lignin ratio.     

Clonal variation for shoot ontogenetic heteroblasty in maritime pine (Pinus pinaster Ait.)

Pine seedling shoots undergo sharp heteroblastic changes during the early ontogenetic stages. The rate of these changes has been seen to vary between species and provenances within species, but there is a marked lack of information about its genetic control at the lower hierarchical levels. We used clonal replicates of maritime pine to determine broad-sense heritability of shoot ontogenetic heteroblasty and its correlation to rooting ability. We applied a simple ontogenetic index based on the proportion of basal nodes with secondary needles in rooted cuttings of 15 clones from 9 environmentally contrasting origins. We found a high clonal heritability for shoot ontogenetic index and a moderately high heritability for rooting ability, but both genetic and phenotypic correlations between these two traits were weak and non-significant. These results indicate that both developmental phenomena are genetically controlled, but not strictly associated in this species.     

Phenotypic analysis of first-year traits in a pseudo-backcross {(slash x loblolly) x slash} and the open-pollinated families of the pure-species progenitors

A single test, including one pseudo-backcross (Pinus elliottii x Pinus taeda) x P. elliottii and open-pollinated families of the pure species progenitors, was established in North Central Florida in December 2007 to study the transfer of the fast-growing characteristics from a P. taeda L. (loblolly pine) parent into the P. elliottii Engelm. (slash pine) background. Several traits were measured in the first growing season: height growth, phenology, tip moth incidence, stem traits, crown architectural and needle traits. Heterosis was evaluated for each trait using analyses of variance by fitting a linear mixed model. All traits were significantly (p value < 0.05) different among families while the significance for heterosis varied by trait. Positive heterosis was found for average rate of shoot elongation (ASRE), total growth (TG), total height and number of needles per fascicle while the opposite was true for base diameter, top diameter, fascicle length, fascicle diameter, crown projected area and phenological traits (cessation, duration and day to reach 50% of the height). Average performance (i.e., no heterosis) was found for initiation of growth, number of branches, number of nodes, tip moth incidence, sheath length and specific leaf area. The analyses indicated that introgression of loblolly pine alleles into slash pine was effective and novel trait combinations were achieved. The pseudo-backcross had larger variation in early height growth than the slash pine families and was taller than all open-pollinated families at the end of the first season. Tip moth incidence was much lower than the loblolly pine family.     

Methods to predict transgressive segregation in barley and other self-pollinated crops

Most of agronomically important characters are biometric traits. An improvement of these traits in cultivated plants by deriving segregants superior to parents, which could be developed as cultivars, is a main goal in breeding of self-pollinated crops. Two problems need to be solved: when will the progeny be better than its parents and how can a genetic potential of a given pair of parental genotypes be predicted? In this paper, transgressive segregation in homozygous barley populations is shortly reviewed. Various approaches to choosing parental forms are shown, and a theoretical method for predicting the frequency of transgressive segregants in a homozygous population is presented. Additionally, relationships between parental diversity estimated with molecular markers and the progeny performance are discussed. Although the prediction of transgressive segregation is still a problem, it seems promising to apply an approach measuring the performance of the parental genotypes and estimating their genetic distance by molecular markers.     

The characterization of wheat genotypes for salinity tolerance using morpho-physiological indices under hydroponic conditions

Salinity affects plant growth, development, yield, and is a big challenge for wheat growth across the globe. Possible feasible solution is creation of salt-tolerant material, genetic variation is a criterion to developing genetically superior individuals. To assess the genetic variation for salt tolerance, nationally and internationally-derived 81 wheat genotypes were selected and evaluated in 0- and 150-mM salt in nutritional culture at seedling stage. Results indicate that salinity levels reveal significant (p ≤ 0.01) differences for fresh root weight (RW), shoot length (SL), fresh shoot weight (SW), total plant length (TL), total fresh weight (TW), root/shoot weight ratio (RSWR), root/shoot length ratio (RSLR), and relative growth rate for weight (RGR-Wt). While, there was no difference for root length (RL). Hierarchical Clustering and Pairwise correlation analysis showed TW, RGR-Wt, SL, SW, and RW were positively correlated among themselves, whereas RL had poor correlations with all the traits except TL and RSLR. Hence, selection of SL can improve the performance of other parameters. Based on PCA analysis, SW and RGR-Wt were the major discriminative components for wheat genotypes. Present study explained that shoot related parameters could be used as a selection criterion to categorize salt-tolerant genotypes. Outperforming genotypes 1104 and 1106 in saline conditions could be used as parents in creation of salt-tolerant wheat genotypes, and parameters such as SL, SW, TW, and RGR-Wt for early screening will be important for creating salt-tolerant and high yielding wheat genotypes.     

Influences of testing sites on the genetic correlations in open-pollinated family trials of Pinus elliottii in South Africa

Summary Two series of open-pollinated family trials of Pinus elliottii, the so-called foreign selection series and the Zululand selection series were repeated, respectively, on four and three sites situated in sub-tropical and cooler-temperate climates of the summer rainfall and constant rainfall areas of South Africa. These series were studied in order to determine how testing sites influence the genetic correlations between traits commonly measured in progeny trials. No trend was detected between site index and genetic correlation, but site drastically changed the size and sign of the genetic correlations between growth traits and stem form. Even the genetic correlation between height and diameter at breast height was strongly affected by site.     

Predicting within-family variability in juvenile height growth of <Emphasis Type="Italic">Salix</Emphasis> based upon similarity among parental AFLP fingerprints

Willow is being developed as a crop for biomass plantations in the Northeast and North-central United States, but has only recently been the subject of controlled breeding to generate improved genotypes. Maximizing variability among progeny within full-sib families produced by controlled pollination may increase the probability of producing willow clones exhibiting desirable extreme phenotypes. Yet, predicting combinations of parents yielding highly variable progeny is not currently possible. Controlled pollinations were completed among 15 Salix eriocephala clones and the resulting progeny were vegetatively propagated and planted in a greenhouse progeny test. Heights of rooted cuttings were measured after 4 months of growth. Genetic similarity among parents was estimated based on 77 polymorphic AFLP bands. Strong negative correlation (r = -0.88) was detected between mean female-parent similarity indices and the standard deviation of height among half-sib progeny from those females. Parent combinations that had relatively low similarity indices tended to produce progeny that had greater variability in height. This negative relationship suggests that AFLP fingerprints of S. eriocephala parents may be useful for predicting parent combinations that will yield families with large variability.     

Genetic control of growth,biomass allocation,and survival under drought stress in Pinus radiata D. Don seedlings

Drought is one of the critical factors limiting plant growth, and knowledge about genetic adaptation to drought is necessary to develop strategies for successful reforestation on drought-prone sites. In this study, genetic variation was investigated in 98 full- and half-sib radiata pine (Pinus radiata D. Don) families, representing Chilean coastal and interior populations, subjected to two water regimes: well-watered and drought-stressed. Assessed traits, in 5-month-old seedlings, included height (H), diameter (D), height-to-diameter ratio (HDR), dry biomass of needles (NDW), stem (SDW), roots (RDW), and total (TDW), root-to-shoot ratio (RSR), and survival (SUR). After 115 days of treatment, growth, biomass, and survival were nearly two times higher under the well-watered regime than under the stressed one. Families differed significantly in most traits, with individual tree heritabilities ranging from 0.14 for SUR to 0.63 for D in the well-watered treatment. Families from the interior showed the highest heritability for D, SDW, RDW, and TDW when grown in the water-stress treatment. The genetic correlations between treatments were moderately strong, which suggests the presence of a genotype by watering regime interaction. Most traits were strongly correlated (genetic correlations often exceeded 0.40). Compared to the first generation families from coastal sites, the third generation families from the interior sites showed an increase in SUR and RSR. Thus, potential exists to screen families at the seedling stage for drought hardiness and to identify parents from the interior sites with potential to produce a more drought-resistant breed with satisfactory growth rates and yields in dry environments.     

Genetic correlation estimations between artificial insemination sire performances and their progeny beef traits both measured in test stations

In France, beef traits of artificial insemination (AI) beef bulls are improved through the sequential selection for their own performances and for their male progeny performances, both being recorded in test stations. The efficiency of such programmes mainly depends on the genetic correlations between sire performances and progeny beef traits. Such correlations were independently estimated, using the multivariate REML (restricted maximum likelihood) method in a Limousin and a Charolais programme. In both breeds, high genetic correlations were observed between sires and progeny analogous morphology scores (from 0.64 to 0.82). Genetic correlations estimated between sires and progeny growth (from 0.41 to 0.70) were lower probably due to the difference of diet in central and progeny stations. Correlations between sire muscling scores and progeny skeletal frames (and vice-versa) were negative (from -0.05 to -0.58). The genetic correlations of sire traits with progeny dressing percentage (DP_p) and carcass fatness score (CF_p) were only low to moderate. These results show that the selection of bulls at the end of performance testing in test stations may be efficient in improving progeny growth and morphology. However, such a selection is insufficient in improving their dressing percentage and carcass composition.     

Genetic correlations between vegetative growth traits and productivity at different within-season intervals for strawberries (Fragaria X ananassa)

Summary Genetic and environmental relationships between vegetative growth and production traits at different intervals within a single season were investigated using unselected strawberry genotypes from 20 biparental crosses and their parents. Vegetative growth and productivity patterns differed between test locations and larger yields were detected where fall growth was greatest. Positive genetic correlations were detected between fall growth increments and mid-season production traits, but fall growth was uncorrelated or negatively correlated with late-season production. Conversely, growth during the production season was genetically uncorrelated or negatively correlated to early production traits, but was positively correlated to mid and late-season production. Together, these results suggest that the growth pattern required for early vs sustained production may represent conflicting breeding objectives. Also, although vegetative and reproductive functions compete for assimilates in strawberry, sustained productivity appears dependent on adequate vegetative growth throughout the spring and early summer. Significant correlations were detected between fall plant growth and early yield, but these were attributed to environmental rather than genetic sources. Genetic correlations between spring growth and early production traits were significantly negative and large, suggesting that vegetative during this interval may indicate limited fall inflorescence development.     

Quantitative genetic analysis of plant growth: biases arising from vegetative propagation

Propagation through vegetative cuttings is a widely used technique that may bias estimates of genetic and environmental effects on plant growth. Leafy stem cuttings from 210 genotypes from eight populations of Salix pulchra were rooted and raised at three levels of nitrogen availability. Cuttings showed a complex suite of responses to vegetative propagation. Population and/or genotypic variation in response to vegetative propagation was observed in (1) retention of leaves during rooting, (2) date that cuttings resumed shoot growth after rooting, and (3) the frequency of cuttings that remained shoot dormant throughout the experiment. Nitrogen treatments also caused different responses to vegetative propagation, influencing date that cuttings resumed shoot growth and frequency of shoot dormancy. Because each of these responses had a direct effect on final plant size, I concluded that final size was a product of both differences among genotypes and treatments in plant growth rate, as well as genotype- and treatment-specific responses to vegetative propagation. This study shows that plant growth experiments can be designed to quantify responses to vegetative propagation and statistically remove these artifacts of propagation from estimates of genetic and environmental effects on plant growth.     

Genetic variation in Eucalyptus nitens pulpwood and wood shrinkage traits

Eucalyptus nitens plantations are generally established for pulpwood production but an increasing area is being managed for solid wood. Genetic variation in, and correlations among, three Kraft pulpwood traits (diameter at breast height, basic density and near-infrared-predicted cellulose content) and three 12-mm wood-core shrinkage traits (recoverable collapse, net shrinkage and gross shrinkage) were examined, utilising data from two 9-year-old first-generation progeny trials in Tasmania. These trials contained approximately 400 open-pollinated families (over 100 of which were sampled for wood properties) representing three central-Victorian E. nitens races. Significant genetic variation at the race and/or within-race level was identified in all traits. Within races, relative levels of additive genetic variation were higher for shrinkage traits, although narrow-sense heritabilities were lower and the expression of genetic variation less stable across sites than for other wood property traits. Heterogeneous intertrait genetic correlations were identified across sites between growth and some wood property traits. However, where significant, genetic correlations indicated that within-race selection for growth would adversely affect core basic density and all core shrinkage traits. Furthermore, results based on cores suggested that within-race selection for higher basic density would favourably impact on cellulose content and collapse but selection for either higher basic density or cellulose content would adversely affect net shrinkage. Most within-race genetic variation in gross shrinkage appeared to be due to genetic variation in collapse. The implications of these results for sawn timber breeding will depend on the strength of genetic correlations between core traits and rotation-age objective traits and objective trait economic weights.     

Postcopulatory fertilization bias as a form of cryptic sexual selection

Males and females share most of their genetic material yet often experience very different selection pressures. Some traits that are adaptive when expressed in males may therefore be maladaptive when expressed in females. Recent studies demonstrating negative correlations in fitness between parents and their opposite-sex progeny suggest that natural selection may favor a reduction in trait correlations between the sexes to partially mitigate intralocus sexual conflict. We studied sex-specific forms of selection acting in Anolis lizards in the Greater Antilles, a group for which the importance of natural selection has been well documented in species-level diversification, but for which less is known about sexual selection. Using the brown anole (Anolis sagrei), we measured fitness-related variation in morphology (body size), and variation in two traits reflecting whole animal physiological condition: running endurance and immune function. Correlations between body size and physiological traits were opposite between males and females and the form of natural selection acting on physiological traits significantly differed between the sexes. Moreover, physiological traits in progeny were correlated with the body-size of their sires, but correlations were null or even negative between parents and their opposite-sex progeny. Although results based on phenotypic and genetic correlations, as well as the action of natural selection, suggest the potential for intralocus sexual conflict, females used sire body size as a cue to sort sperm for the production of either sons or daughters. Our results suggest that intralocus sexual conflict may be at least partly resolved through post-copulatory sperm choice in A. sagrei.     

Genetic determinism of the vegetative and reproductive traits in an F1 olive tree progeny

The agronomic performance of fruit trees is significantly influenced by tree internal organization. Introducing architectural traits in breeding programs could thus lead to select new varieties with a regular bearing and lower input demand in order to reduce training and environmental costs. However, an interaction between tree ontogeny and genetic factors is expected. In this study, we investigated the genetic determinism of architectural traits in the olive tree, accounting for tree development over 5 years until first flowering occurrence. We studied an F1 progeny issued from a cross between two contrasted genotypes, ‘Olivière’ and ‘Arbequina’. Tree architecture was decomposed in quantitative traits, related to (1) growth and branching, (2) first flowering and fruiting. Models, including the year of growth, branching order and genotype effects, were built with variance function and covariance structure when necessary. After a model selection, broad sense heritabilities were calculated. During the first 3 years, both the mean values of vegetative traits and genetic factor significance depended on the shoot within-tree position. Dependencies between consecutive years were revealed for traits related to whole tree form. Whole tree form variables showed medium to high broad sense heritability values, whereas reproductive traits were highly heritable. This study demonstrates the existence of ontogenic trends in the olive tree, which result in traits heritable only at the tree periphery. A phenotyping strategy adapted to its architectural characteristics and a list of relevant traits, such as maximal internode length, is proposed. Transgressive effects suggest that genetic progress could be performed in future selection programs.     

Variances and covariances of phenological traits in a wild mammal population

In a seasonal environment, there are multiple aspects of timing, or phenology, that contribute to an individual's fitness. Several studies have shown a genetic basis to variation between individuals in breeding time, but we know little about the heritability of other phenological traits in wild populations. Furthermore, the presence of genetic correlations between phenological variables could act to constrain or promote any response to selection, but less is known of the multivariate genetic relationships underlying phenological traits in the wild. Here, we use data from a wild population of red deer on the Isle of Rum, Scotland, to investigate covariances between eight phenological traits. Variation was characterized at the level of the phenotype, genotype, and year, and traits measured in different sexes enabled us to test for cross-sex genetic correlations. Phenotypic correlations were broadly strong and positive, as were correlations between traits expressed in the same year. We found evidence of significant additive genetic variation in five of the eight phenological traits studied. However there was little evidence of genetic correlations between traits, implying that much of the observed phenotypic correlation was environmentally induced. Our results suggest that different phenological traits may be free to move along independent evolutionary trajectories.     

Genetic dissection of fusiform rust and pitch canker disease traits in loblolly pine

Loblolly pine (Pinus taeda L.) exhibits genetic resistance to fusiform rust disease (incited by the biotrophic fungus, Cronartium quercuum f. sp. fusiforme) and pitch canker disease (incited by the necrotrophic fungus, Fusarium circinatum). In this study, a total of 14,015 loblolly pine cuttings from 1,065 clones were screened in controlled greenhouse conditions to identify phenotypes of clones, families, and parents that guide a genetic dissection of disease traits associated with pitch canker and fusiform rust. A total of 23,373 phenotypic data points were collected for lesion length (pitch canker) and gall score, gall length, and gall width (fusiform rust). We verified heritable fusiform rust and pitch canker traits and calculated parental, clonal, and full-sib family rankings for both diseases. Genetic correlations revealed that traits associated with fusiform rust are genetically distinct from one another, and that the genetic mechanisms underlying pitch canker and fusiform rust resistance are independent. The disease phenotyping described here is a critical step towards identifying specific loci and alleles associated with fusiform rust and pitch canker resistance.