Wide range QTL analysis for complex architectural traits in a 1-year-old apple progeny.

The present study aimed at investigating the genetic determinisms of architectural traits in a 1-year-old apple (Malus x domestica Borkh.). F1 progeny. A precise phenotyping including both tree topology and geometry was performed on 123 offspring. For a wide range of developmental traits, broad-sense heritability was estimated and quantitative trait loci (QTLs) were investigated. Several loci controlling geometry were identified (i) for integrated traits, such as tree surface and volume; (ii) for traits related to the form of long sylleptic axillary shoots (LSAS), such as bending and basis angle; and (iii) for traits of finer components, such as internode length of the trunk and LSAS. Considering topology, 4 QTLs were mapped for the total number of sylleptic branching in the tree, suggesting a strong and complex genetic control that was analysed through colocalisations between QTLs mapped for the different shoot types (long, medium, short). Two QTLs were also mapped for a phenological trait (date of bud break). When several QTLs were detected for a trait, a linear model was built to test epistatic effects and estimate the whole percentage of variability explained. The discussion focuses on particular colocalisations and on the relevance of traits to further tree development.     

Growth Dynamics and Morphology of Annual Shoots, According to their Architectural Position, in Young Cedrus atlantica (Endl.) Manetti ex Carriere (Pinaceae)

The influence of shoot architectural position on growth andbranching pattern of young Cedrus atlantica (Endl.) Manettiex Carrière trees were studied. Extension growth andtype of axillary products (lateral bud, sylleptic short or longshoots) of annual shoots of increasing branching order (mainstem, branches and branchlets) were recorded weekly during the1993 growing season. Annual final shoot length, duration ofextension, and maximum extension rate decreased with increasingbranching order. Sylleptic axillary shoots occurred only onannual shoots of the main stem and branches and were producedwhen extension rate was at its highest. Differences in growthrate and final length of annual shoots, according to their architecturalposition, were related to differences in the total number anddiversity of types of sylleptic axillary shoots produced. Itis suggested that types and numbers of sylleptic axillary shootsproduced are linked with threshold values for both final lengthand extension rate of the parent shoot. Copyright 1999 Annalsof Botany Company Atlas cedar, extension growth, sylleptic branching, tree architecture, morphology.     

Architectural analysis of 1-year-old apple seedlings according to main shoot growth and sylleptic branching characteristics

Main shoot and sylleptic shoot growth characteristics were measured during and after the first year of growth of 255 Telamon x Braeburn apple seedlings. Although mean main shoot growth characteristics between branched and non-branched trees were significantly different, many non-branched trees expressed similar main shoot growth to branched trees. The variables describing length, number and position of the sylleptic shoots were used to classify branched trees into architecturally different groups. A continuum from trees with few and short shoots to trees with many long shoots is observed. The release of axillary buds from apical dominance is not under complete control by the apical meristem. Genetic seedling difference at the level of roots presumably plays an important role in sylleptic branching. Genetic variation in terms of number, position, and subsequent elongation of sylleptic shoots is clearly observed.     

Phenotypic Plasticity of Sylleptic Branching: Genetic Design of Tree Architecture

The crown of many trees is composed of a main axis and branches. All branches arise from axillary or lateral buds and two types of branches exist: proleptic and sylleptic. Proleptic branches form from buds that have undergone a rest period, typically associated with winter dormancy, whereas sylleptic branches emerge without a rest and without complete bud formation. All trees have proleptic branches; some trees with the indeterminant growth habit have both proleptic and sylleptic branches. Sylleptic branches may play an important role in determining tree growth, architecture and adaptation for many temperate-zone woody plants. We review evidence for the phenotypic plasticity of sylleptic branches and its genetic, environmental, and developmental control.     

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.     

Growth Context and Fate of Axillary Meristems of Young Peach Trees. Influence of Parent Shoot Growth Characteristics and of Emergence Date

The relationship between several growth components of a shootand the fates of the axillary meristems (developing in the axilsof the leaves) borne by that shoot were studied, on first-ordershoots of young peach trees. A comprehensive picture of thoserelationships was obtained by a discriminant analysis. Shootgrowth at meristem emergence date was characterized by internodelength, leaf-production rate and leaf-unfolding duration. Allpossible fates of axillary meristems at the end of the growingseason (i.e. blind nodes, single vegetative or flower bud, budassociations, sylleptic or proleptic shoots) were considered.Shoot-elongation rate determined meristem fates quantitatively.The number of buds produced by a meristem increased when theshoot-elongation rate increased. Qualitatively, the fate of axillary meristems was related tothe balance between shoot-growth components. If the subtendingleaf unfolded slowly, sylleptic or proleptic shoots were morelikely to develop than bud associations, for high shoot-elongationrates; and flower buds were more frequent than vegetative buds,for low shoot-elongation rates. Compared to flower buds, blindnodes appeared for similar shoot-elongation rates but longerinternodes and lower leaf-production rates. The emergence dateslightly modified the relation between shoot growth and axillary-meristemfates, but the main features held true throughout the growingseason. The relationships between shoot growth and meristem fates mayresult from competitive interactions between the growing subtendingleaf and the developing axillary meristem. Growing conditionsmight also influence both shoot growth and meristem fates byfavouring either cell enlargement or cell division.Copyright1995, 1999 Academic Press Peach tree, Prunus persica (L.) Batsch, axillary meristem, meristem fate, branching, flowering, shoot growth, discriminant analysis, exploratory analysis     

桃树修剪分枝模式的模拟

在不同修剪手法下,对栽培桃树(Prunuspersica(L.)Batsch)不同母枝上的分枝模式进行了比较研究.从分枝模式来看:修剪后的母枝基本由3个不同的区域组成,基部是不萌发的潜伏芽形成的未分枝区域;中部是延迟分枝和多次分枝组成的分枝区域(主要的枝条类型有短枝、长枝和多次枝);顶部是被剪除的部分.我们通过隐式半马尔可夫模型来模拟这一分枝模式,主要是定量描述1次枝和多次枝在母枝上的数量及其分布状况.在上述模型中,未分枝区、延迟分枝区和多次分枝区称为瞬时态,被剪除的部分称为吸收态.模拟的结果与观察的结果进行对比后发现,两者具有很好的一致性.这说明隐式半马尔可夫模型是模拟植物分枝过程的一种有效方法,尽管隐式半马尔可夫链模型只是一个描述性的模型,但仍能对其所描述的生物现象进行解释,在预测修剪手法对母枝分枝模式影响方面比传统的方法具有明显的优势.本研究结果是建立三维虚拟桃树树冠分枝结构的基础.     

Relationship between reproductive behavior and new shoot development in 5-year-old branches of olive trees (Olea europaea L.)

The development of new shoots plays a central role in the complex interactions determining vegetative and reproductive growth in woody plants. To explore this role we evaluated the new shoots in the olive tree, Olea europaea L., and the effect of fruiting on new shoot growth and subsequent flowering. Five-year-old branches served as canopy subunits in order to obtain a global, whole-tree view of new shoot number, size and morphological origin. The non-bearing trees had many more shoots than the fruit-bearing trees, and a greater number of longer shoots. In both bearing conditions, however, the majority of shoots were less than 4 cm long, with shoots of progressively longer lengths present in successively decreasing frequencies. Six major shoot types were defined on the basis of apical or lateral bud origin and of parent shoot age. On fruit-bearing trees, the new shoots originated predominantly from the shoot apex, while on non-fruiting trees, they formed mainly from axillary buds, but in both cases, they tended to develop on younger parent shoots. The previous bearing condition of the tree was the main determinant for subsequent inflorescence development, which was independent of both shoot type and length. Thus, reproductive behavior strongly affected both the amount and type of new branching, but subsequent flowering level was more influenced by previous bearing than by the potential flowering sites on new shoots.     

Sylleptic branching in winter-headed apple (<Emphasis Type="Italic">Malus × domestica)</Emphasis> trees: accession-dependent responses and their relationships with other tree architectural characteristics

Well-feathered apple trees are essential for commercial orchards to optimize yields. However, most cultivars do not form these sylleptic branches readily in commercial nurseries due to high apical dominance. Several treatments exist to promote their formation in the nurseries, one of which is heading. However, not all cultivars are expected to react similarly to these treatments. We studied the branching response of 155 genotypes following heading and its relation to other architectural traits as a function of the cultivar’s genetic background. Trees were grown for two consecutive years after grafting in a nursery, and the main axes were headed in the winter following growth in year 1. After heading, a single shoot was retained when growth resumed in the second year. Plant architectural traits such as growth of the main shoot, internode length, sylleptic branching, etc. were measured before and after heading and were statistically compared using a mixed model. This model showed the effect of heading for all architectural traits studied. In addition significant genotype and genotype × treatment interactions were found. In general, genotypes that showed a more vigorous growth during the first year also reacted more vigorously to heading. Accounting for the genetic substructure of this collection, no clear distinction in tree response could be found except in a small group of individuals that belonged to an F1 mapping population. This study shows that heading is not favorable for all genotypes to promote sufficient sylleptic branching and that other methods are needed to promote branching in these accessions.     

Influence of the variation of geometrical and topological traits on light interception efficiency of apple trees: sensitivity analysis and metamodelling for ideotype definition

Background and Aims

The impact of a fruit tree''s architecture on its performance is still under debate, especially with regard to the definition of varietal ideotypes and the selection of architectural traits in breeding programmes. This study aimed at providing proof that a modelling approach can contribute to this debate, by using in silico exploration of different combinations of traits and their consequences on light interception, here considered as one of the key parameters to optimize fruit tree production.

Methods

The variability of organ geometrical traits, previously described in a bi-parental population, was used to simulate 1- to 5-year-old apple trees (Malus × domestica). Branching sequences along trunks observed during the first year of growth of the same hybrid trees were used to initiate the simulations, and hidden semi-Markov chains previously parameterized were used in subsequent years. Tree total leaf area (TLA) and silhouette to total area ratio (STAR) values were estimated, and a sensitivity analysis was performed, based on a metamodelling approach and a generalized additive model (GAM), to analyse the relative impact of organ geometry and lateral shoot types on STAR.

Key Results

A larger increase over years in TLA mean and variance was generated by varying branching along trunks than by varying organ geometry, whereas the inverse was observed for STAR, where mean values stabilized from year 3 to year 5. The internode length and leaf area had the highest impact on STAR, whereas long sylleptic shoots had a more significant effect than proleptic shoots. Although the GAM did not account for interactions, the additive effects of the geometrical factors explained >90% of STAR variation, but much less in the case of branching factors.

Conclusions

This study demonstrates that the proposed modelling approach could contribute to screening architectural traits and their relative impact on tree performance, here viewed through light interception. Even though trait combinations and antagonism will need further investigation, the approach opens up new perspectives for breeding and genetic selection to be assisted by varietal ideotype definition.     

Quantitative genetics of yield breeding forPopulus short rotation culture. III. Efficiency of indirect selection on tree geometry

Quantitative analysis of genetic covariances was used to identify the critical morphological components of wood productivity and to evaluate the efficiency of indirect selection for these components at the four levels of biological organization, (1) leaf, (2) branch, (3) main stem, and (4) whole-tree, in 4-yearPopulus deltoides ×P. simonii andP. deltoides ×P. nigra F₁ progeny. A total of 44 morphometric traits measured at the four organizational levels showed varying genetic associations with productivity, variations being dependent on traits, developmental processes (current terminal, sylleptics, and proleptics), and hybridization combinations. Most of the leaf and branch traits on the current terminal and/or sylleptic branches had higher genetic correlations with stem-wood volume than those on proleptics, which resulted in larger indirect selection responses in volume, especially in DxS progeny. Indirect clonal selection on leaf size and area, branching capacity, and branch angle at age 4 years was expected to generate 10–35% more genetic gain per year in 6-year volume than direct selection on 6-year volume in the DxS progeny. The efficiency of indirect selection on the numbers of different order branches and bifurcation ratio was greater than 1.0 relative to that for direct selection for stemwood volume in the D × N progeny. Under the pressure of artificial selection for superior volume production, with the proportion selected=15%, the two F₁ progeny populations exhibited distinct evolutionary divergence in tree geometry. The high-yielding D × S clones displayed a decurrent-like crown with strong apical dominance, whereas the crown ideotype for the high-yielding D × N clones was found to be excurrent-like and surrounded by dense foliage and branches.     

Genetic determinism of anatomical and hydraulic traits within an apple progeny

The apple tree is known to have an isohydric behaviour, maintaining rather constant leaf water potential in soil with low water status and/or under high evaporative demand. However, little is known on the xylem water transport from roots to leaves from the two perspectives of efficiency and safety, and on its genetic variability. We analysed 16 traits related to hydraulic efficiency and safety, and anatomical traits in apple stems, and the relationships between them. Most variables were found heritable, and we investigated the determinism underlying their genetic control through a quantitative trait loci (QTL) analysis on 90 genotypes from the same progeny. Principal component analysis (PCA) revealed that all traits related to efficiency, whether hydraulic conductivity, vessel number and area or wood area, were included in the first PC, whereas the second PC included the safety variables, thus confirming the absence of trade-off between these two sets of traits. Our results demonstrated that clustered variables were characterized by common genomic regions. Together with previous results on the same progeny, our study substantiated that hydraulic efficiency traits co-localized with traits identified for tree growth and fruit production.     

The effect of air temperature in successive periods of the growing season on sylleptic shoot formation in young apple trees

In two day-light phytotron rooms young apple trees were exposed to either 15 or 25°C in three successive periods of six weeks (Periods I, II and III) starting in the beginning of the growing season. A control group was kept outside throughout. Exposure to 15°C in either period had little effect on sylleptic growth; there was also hardly any difference with the outside treatment. At 25°C total sylleptic growth was greatly favoured especially when that temperature was applied in all three periods. However, 25°C given continuously did not affect sylleptic shoot number in Period II and III, but applied only in Period II or III greatly enhanced it. In a few cases there was a positive carry-over effect of 25°C given in Period I or II on sylleptic growth in the next period. No such carry-over effect was found for shoot number. Although temperature did influence growth of the parent shoot, that influence was much smaller than for sylleptic growth. The outgrowth of sylleptic shoots mainly occurred in periods when growth vigour of the parent shoot was highest. The distribution of sylleptic shoots along the parent shoot was greatly affected by the period in which the temperature of 25°C was applied suggesting that buds are only able to respond to outgrowth-inducing factors in a certain stage of development.     

Seeing the trees for the leaves – oaks as mosaics for a host-specific moth

From the perspective of a specialist herbivore, how homogenous are individual tree crowns as patches of habitat? We partitioned variation in physical and chemical host leaf traits and in the abundance and performance of a specialist oak leaf miner, Tischeria ekebladella, into variation at different hierarchical levels. For the phenolic contents of the leaves, we examined variation among oak stands, among trees within stands and among branches within trees. For leaf size and water content, we assessed variation among trees within a single stand, among shoots within trees, and among leaves within shoots. For moth abundance and performance, we examined variation across all levels: among oak stands, among trees within stands, among branches within trees, among shoots within branches and among leaves and insect individuals. For measures of phenolic contents, we found little variation among stands but substantial variation among individual trees. Yet, a tree particularly rich in a given compound was often comparatively poor in another. At a finer spatial scale, the phenolic composition of individual parts of a single tree was quite consistent, whereas leaf weight and water content varied widely within individual tree crowns. Moth abundances varied more among shoots within branches than at any other spatial level, whereas moth survival showed equal levels of variation within individual shoots as among separate oak stands. Likewise, for four other measures of larval performance (assessed at the level of trees and lower), we found more variation within than between trees. In conclusion, the large variation observed in the performance of a specialist moth and in the physical traits of the leaves among different parts of single tree crowns refutes the image of an oak tree as an ‘island’ of internally homogeneous quality. Hence, we may expect little evolutionary adaptation of T. ekebladella at the scale of individual trees. The moths may instead evolve to behaviourally select their resource at a very fine scale. Large variation within trees also calls for extensive replication within trees in ecological sampling designs and/or the sampling of maximally similar leaves.     

Preformed and neoformed extension of shoots and sylleptic branching in relation to shoot length in Tsuga canadensis

Summary Shoot systems developed over 3 successive years were investigated on 55 understorey Tsuga canadensis (L.) Carr. trees. Paired comparisons of preformed-leaf content of terminal buds and numbers of leaves produced on new shoots showed that neoformed leaves were produced in large numbers. Parent-shoot character was not useful in predicting numbers of preformed leaves, was better related to total leaves produced, but left the majority of the variation unexplained. This reflected the capacity of any terminal bud to produce a shoot with more or less neoformation, depending on conditions for growth. All shoots over 6 cm long produced sylleptic shoots that bore from two to many leaves and were arranged in a mesitonic pattern along the parent. Some of the longer sylleptic shoots produced lateral buds or second-order sylleptic shoots. Monopodial second-year extensions of sylleptic-shoot axes followed an acrotonic pattern, as did proleptic shoots from the few lateral buds borne on the parent shoots. Such lateral buds were more frequent on shorter parent shoots: they typically occurred near the proximal and distal ends. Duration of shoot extension was positively correlated with shoot length: terminal buds became evident as shoot extension neared cessation.     

Responses of crown architecture in Betula pendula to competition are dependent on the species of neighbouring trees

We measured the growth responses of individual shoots and branches of Betula pendula when growing next to trees of the same species or Pinus sylvestris, Larix sibirica or Alnus glutinosa. We used the three-dimensionally digitized response variables and the size and distance of trees growing within a 5-m radius of the study trees to establish a relationship between tree performance and the effect of competing neighbouring tree species on crown architecture. B. pendula was able to modify its crown architecture and thus alter its strategy to compete with different neighbours. Trees of B. pendula growing beside species counterparts had the highest growth of new long shoots in relation to the already existing branch length [growth vigour (GV)], while GV was the lowest next to L. sibirica. With B. pendula or P. sylvestris as its main neighbour, B. pendula invested in short shoots by growing them rather densely in short branches with limited numbers, whereas with L. sibirica the number, length and angle of the branches were high. The competitive response was also strongly dependent on tree ontogeny and the shoot and branch characteristics were significantly affected by their location inside the crown. B. pendula was able to respond to the challenges posed by its neighbours, which was also reflected in the GV. The ability to maintain steady growth with alternative crown designs in different neighbourhoods reflects plasticity in the crown responses.     

Dissecting apple tree architecture into genetic, ontogenetic and environmental effects: QTL mapping

The present study aimed to dissect tree architectural plasticity into genetic, ontogenetic and environmental effects over the first 4 years of growth of an apple F1 progeny by means of quantitative traits loci (QTL) mapping. Both growth and branching processes were phenotyped on the consecutive annual shoots of different axes within a tree. For each studied trait, predicted values (best linear unbiased predictors, BLUPs) of the genotypic (G) effect or its interaction with tree age (G×A) and climatic year (G×Y) were extracted from mixed linear models of repeated data. These BLUPs, which are independent from autocorrelations between repeated measurements, were used for QTL mapping. QTL detection power was improved by this two-step approach. For each architectural process, numerous QTLs were detected and some particularly interesting co-localised in common genomic regions, for internode lengthening, top diameter, and number and percentage of axillary shoots. When several QTLs were detected for a given trait, global models were estimated, which explained a maximum of 40% of the total variance for both internode length and top diameter and 28% for branching. QTLs detected for BLUPs of G×Y effects were interpreted as resulting from the interaction between genetic maximal potential of growth and climatic factors, while those for G×A effects were interpreted in relation to tree ontogeny. Most of the latter ones were found to be concomitant with key development stages during which the trait average started to decrease, but with different magnitudes depending on genotype. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Genetic mapping of QTLs affecting tree growth and architecture in Populus: implication for ideotype breeding

 A segregated F₂ progeny derived from two highly divergent poplar species, Populus trichocarpa and P. deltoides, was used to evaluate the genetic basis of canopy structure and function in a clonally replicated plantation. The QTLs of large effect on growth, branch, and leaf traits were identified using the Populus linkage map constructed by 343 molecular markers. Stem height and harvest index appeared to be under the control of few QTLs with major effects, whereas variation in stem basal area, volume, and dry weight might be due to many more QTLs. Branch and leaf traits on sylleptics tended to include more QTLs with major effects than those on proleptics. In the environment where the pedigree was tested, sylleptics were very frequent in the P. trichocarpa parent but rare in the P. deltoides parent. For sylleptic traits for which two or more QTLs were identified, however, increases in the trait values were conditioned not only by the P. trichocarpa alleles, but also by the P. deltoides alleles. Similar findings were found for traits on proleptics that were differently expressed between the two parents. For both sylleptic and proleptic branch types, dominance (ranging from partial to over) was observed. The QTLs on specific linkage groups were found to be responsible for relationships between stem growth and its developmental components. Similar QTL clustering was also observed for morphological or developmental integration in poplar, i.e., traits with similar developmental origins are more strongly correlated with one another than traits with different developmental origins. The implications of these molecular genetic results for ideotype breeding of poplars are discussed. Received: 15 July 1997/Accepted: 19 August 1997     

Relationship of Pruning and Growth Morphology with Hormone Ratios in Shoots of Pillar and Standard Peach Trees

Genotype and cultural management determine the shape of peach [Prunus persica (L.) Batch] tree canopies in orchards. Not well understood, however, is the relationship between terminal growth, lateral branching, and shoot hormone levels that can fundamentally affect tree canopy development. In this experiment, two peach cultivars with widely differing growth habits (Pillar, KV930479 and Standard, ‘Harrow Beauty’) were budded on ‘Lovell’ rootstock, planted in the field in 1998, and characterized for shoot morphology and hormone concentrations in 2002 and 2003 (the fourth and fifth leaf, respectively). Auxin (indole-3-acetic acid) and cytokinins (largely trans-zeatin riboside, dihydrozeatin riboside, and isopentenyladenosine) were measured in shoot tips (2002) and current-year shoots (2003) using mass spectrometry. In 2002, Pillar trees had less sylleptic branching, more upright growth, and higher auxin and auxin-to-cytokinin ratios than Standard trees. In Pillar trees in 2003, auxin concentrations and shoot growth were highest in current year shoots; in pruned trees, only auxin levels increased. Peach tree growth habits may be the result of altered hormone metabolism. Growth forms leading to superior production efficiency may be developed by selection based on specific target hormone concentrations and ratios.     

Use of resampling to assess optimal subgroup composition for estimating genetic parameters from progeny trials

Estimations of genetic parameters of wood traits based on reduced sample populations are widely reported in the literature, but few investigations have considered the consequences of these small populations on the precision of parameter estimates. The purpose of this study was to determine an optimal strategy for sampling subgroups, by varying either the number of families or the number of individuals (trees) per family, and by verifying the accuracy of certain genetic parameters (across-trials analysis). To achieve this, simulations were conducted using random resampling without replacement (k?=?1,000/pair of varying factors) on datasets containing 10-year total height of two coniferous species (Larix laricina and Picea mariana), as well as pilodyn measurements of wood density evaluated on a 26-year-old population of P. mariana. SAS® 9.2 Macro Language and Procedures were used to estimate confidence intervals of several genetic parameters with different reduced samplings. Simulation results show that reducing the number of trees per family per site had more impact on the magnitude and precision of genetic parameter estimates than reducing the number of families, especially for half-sib heritability and type B genetic correlations for height and wood density. A priori determination of an optimal subsampling strategy to evaluate the accuracy of genetic parameters should become common practice before assessing wood traits, in tree breeding studies or when planning juvenile retrospective progeny trials for forest tree species.