AOBPreview originally published online on June 26, 2003
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Annals of Botany 92: 317-325, 2003
© 2003 Annals of Botany Company
Genotypic Differences in Branching Pattern and Fruiting Habit in Common Walnut (Juglans regia L.)
TAMPAR11 University of Ljubljana, Biotechnical Faculty, Agronomy Department, Jamnikarjeva 101, 1111 Ljubljana, Slovenia
Received: 8 January 2003; Returned for revision: 31 March 2003; Accepted: 7 May 2003 Published electronically: 26 June 2003
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSLITERATURE CITED |
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Architectural analysis of 840 Slovenian walnut (Juglans regia L.) genotypes was performed to determine the most typical and frequent morphological types and to evaluate their vegetative and generative potential. Four branching and fruiting patterns (I–IV) were detected. A 3-year-old fruiting branch, consisting of a 3-year-old shoot plus corresponding 2-year-old and 1-year-old shoots, was used as a structural unit for quantitative analysis. In the intermediate fruit-bearing types with mesotonic and acrotonic branching pattern (types II and III), the total lengths of 3-, 2- and 1-year-old shoots were 385 and 380 cm, respectively, compared with 275 and 253 cm in the terminal and lateral-fruiting types (types I and IV). In type I, 1-year-old shoots had significantly fewer nodes than in other types. In addition, they had a thinner basal diameter than types III and IV, and their angles were the most erect (39°). Only 0·4 out of 3·6 1-year-old shoots were flowering with one mixed bud with 1·9 female flowers. In type IV, 2-year-old shoots had significantly more nodes and a larger basal diameter than other types. One-year-old shoots in type IV are thicker than those in other types. Ratios between the number of flowering and the total number of 1-year-old shoots were 0·7 in type IV, 0·6 in type III, 0·5 in type II and 0·1 in type I. On 1-year-old shoots in type IV, 1·7 mixed buds with a mean of three female inflorescences per bud were counted. Consequently, the generative potential is highest in type IV and lowest in type I. In types II and III, growth and the ability to bear fruits are more balanced.
Key words: Juglans regia, walnut, genotypic variation, architectural analysis, fruiting branch, generative and vegetative potential.
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSLITERATURE CITED |
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Branching and fruiting patterns are useful features for characterizing tree canopy architecture. They are determined via tree architectural analysis, which allows quantification of the form and shape (Godin et al., 1998). Tree shape is defined by its branching architecture (Ustin et al., 1991), which is a major aspect of the architectural approach to the study of plants (Guédon et al., 2001). The architectural analysis is based on three major architectural concepts: the architectural model, the architectural unit and reiteration (Barthélémy et al., 1991).
The architectural unit of a species represents its fundamental architectural and functional structural component. It is composed of all categories of tree axes (Barthélémy et al., 1991). For any tree species, there is a finite number of axis categories, the nature and relative position of which define the architectural unit (Bell, 1991). The complete or partial repetition of the architectural unit during ontogenesis is a common phenomenon in trees (Barthélémy et al., 1991) and is defined as reiteration (Oldeman, 1974). The result of this process is termed a ‘reiterated complex’. Thus, an adult tree is a stack of reiterations, each of which represents a repetition of an architectural unit (Jaeger and de Reffye, 1992). The architectural model of a tree is the growth pattern that determines its successive architectural phases (Hallé and Oldeman, 1970) and developmental sequence of branching (Bell, 1991). According to Hallé and Oldeman (1970), who described 24 different models for tropical trees, the architectural model is an inherent growth strategy that defines both the manner in which the form of the plant is elaborated and the resulting architecture. The identification of the architectural model is based on four major groups of simple morphological features: type of growth, branching pattern, morphological differentiation of axes and the position of the sex organs (Hallé and Oldeman, 1970; Hallé et al., 1978).
In common walnut (Juglans regia L.), growth is rhythmic with the axis being built up by a succession of annual shoots (Sabatier and Barthélémy, 2001). Flowering or vegetative annual shoots in walnut can be monocyclic, bicyclic (Barthélémy et al., 1995; Ducousso et al., 1995; Sabatier et al., 1995; Sabatier and Barthélémy, 2001) or even tricyclic (Mauget, 1976; Barthélémy et al., 1995; Sabatier and Barthélémy, 2001). Monocyclic shoots are formed by the first growth flush in spring. They are usually completely preformed in winter buds. Bicyclic and tricyclic annual shoots are also generally preformed but in intermediate intra-annual buds (Barthélémy et al., 1995; Sabatier et al., 1995, 1998; Sabatier and Barthélémy, 2001). On the adult tree, monocyclic shoots are usually female, flowering in the terminal position, while the bicyclic and triyclic shoots are mostly vegetative (Barthélémy et al., 1995).
During the juvenile period, the stem of a walnut tree has a monopodial development (Solar, 2000; Sabatier and Barthélémy, 2001), and is built up by the vegetative extension of one single apical meristem (Bell, 1991). Axillary shoots are weaker than the main axis and are in a subordinate position (Denffer and Ziegler, 1988). As a walnut tree ages, the development pattern changes from monopodial to sympodial (Solar, 2000; Sabatier and Barthélémy, 2001). This transition is linked to terminal female flowering. Sympodial axes are built up by a linear series of shoot units. Each new distal shoot unit develops from an axillary bud situated on the previous shoot unit (Bell, 1991). When the axillary shoots are formed, the terminal bud of the main axis may rest, produce a terminal female inflorescence, or die (Denffer and Ziegler, 1988).
Branching in walnut is usually proleptic (Hallé et al., 1978) with branches formed from dormant buds (Bell, 1991; Wu and Hinckley, 2001). In some cases, the main stem develops lateral branches in the same growing season of its extension (Sabatier and Barthélémy, 2001). Such branches are termed sylleptic or immediate (Caraglio and Barthélémy, 1997), and extend simultaneously with the apical meristem of the main stem without displaying a resting period (Bell, 1991) and without complete bud formation (Wu and Hinckley, 2001).
Fruiting habit is described by branching density and by the position of flowering buds on annual shoots. According to Germain (1990, 1992), there are three types of fruit-bearing habit: terminal, intermediate and lateral. Terminal fruit-bearing types display flower buds only on terminal or subterminal parts of the annual shoots that are growing on 3-year-old branches. Intermediate bearers display female flowers mainly on terminal and subterminal buds on the annual shoots when they are inserted on 2-year-old branches. Lateral fruit-bearing types display flowering buds along 1-year-old shoots. Female flowering induction affects terminal and subterminal buds and also the majority of the axillary buds on the current growth shoot.
In the present study, genetic variability in walnut was analysed with respect to branching and fruiting patterns. The research represents a continuation of the previous work started by Germain (1979) and Szentivanyi (1990), who combined terminal fruit-bearing and late-leafing French and Hungarian walnuts with lateral-fruiting Californian cultivars, with the aim of creating late-leafing and lateral fruit-bearing offspring populations, which tend to be more precocious and have a higher yield earlier than those that bear their nuts terminally (McGranahan and Leslie, 1991). Their work was largely based on practical experience. The approach taken in this study is based on exact measurements of the fruit-bearing annual shoots parameters, in order to (a) determine the most frequent morphological types (concerning branching and fruiting patterns) of the walnut progenies in Slovenia, and (b) to identify the differences in generative and vegetative potential among the branching and fruiting types using quantitative analysis of fruiting branches.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSLITERATURE CITED |
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The analysis included a random selection of walnut genotypes belonging to the local population, which grows in the south-eastern part of Slovenia, along the Sotla river valley. The population consisted of 840 individuals developed from randomly selected seeds, which were taken from healthy-looking trees, originating from unknown indigenous genotypes from nearby villages. The phenotypic variability of the population is enormous. Due to a high level of heterozygosity, each tree represented a unique genotype, having grown together with others in the same environment. The 1-year-old seedlings were planted in 1988–1992. The trees were not pruned, fertilized or irrigated, and diseases, weeds and pests were not controlled.
Data collection
During the spring–summer of 1998, in all genotypes a structural unit consisting of ‘a 2-year-old shoot plus corresponding 1-year-old shoots’ was observed to determine its branching pattern (acrotony, mesotony, basitony). The nature of the terminal bud on 1-year-old shoots (flowering, vegetative) was also determined. According to Germain’s (1990) classification, genotypes were divided into terminal, intermediate and lateral types, depending on the distribution of flowering buds on the shoot, the nature of the buds (flowering, vegetative) and the age of the flowering shoot bearer. According to Caraglio et al. (1998), different schemes of a chosen architectural type were drawn in situ. They represented variability in branching and the fruit-bearing pattern of the entire population examined.
From among the great number of architectural schemes described, four were selected because they were the most typical and frequent representatives of certain branching and fruiting types in the population. They are referred to as ‘morphotypes’ and labelled from I to IV.
An architectural scheme was created for each morphotype (Table 1; Fig. 2). The following parameters were defined: trunk development (monopodial, sympodial); orientation (plagiotropy, orthotropy); growth (determinate, indeterminate); branching pattern; and the length of the growth unit, which is defined as the part of the annual shoot produced during one growth flush. Out of the whole population, 25 genotypes—the most typical representatives of each morphotype (i.e. 100 individuals in total)—were selected.
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For quantitative analysis of the walnut canopy architecture, a structural unit was defined as the ‘fruiting branch’ (i.e. a 3-year-old branch plus 2-year-old shoots plus 1-year-old shoots). In each tree, five fruiting branches, symmetrically distributed in the middle of the canopy (in terms of height) and well exposed, were selected. On hundred and twenty-five 3-year-old shoots were analysed with corresponding 2-year-old and 1-year-old shoots for each morphotype. The total number of shoots analysed for all morphotypes was: 500 3-year-old shoots; 2397 2-year-old shoots; and 1345 1-year-old shoots.
During the 1998/1999 dormant season, several measurements were performed on the selected fruiting branches on each 3-, 2- and 1-year-old shoot unit. Three-year-old shoots were marked as ‘N-2’ shoots. Their length was measured. Two-year-old shoots on the 3-year-old base were marked as ‘N-1’ shoots. They were measured for total number of shoots, number of flowering shoots, length, number of nodes, branch angles and basal diameter. One-year-old shoots on the 2-year-old base were marked as ‘N’ shoots. They were measured for total number of shoots, number of flowering shoots, length, number of nodes, branch angles, basal diameter, number of vegetative buds, number of mixed buds and number of female flowers. Shoot length was measured in centimetres, from the base to the top, using a fabric tape measure. Nodes were counted from the base of a shoot towards the top—from the first to the last still distinguishable node. The angles of shoots were determined using a special goniometer where lower values (in degrees) represented more erect shoots. The angle of an N shoot was represented by the value (°) measured between an N shoot and an N-1 shoot, and the angle of an N-1 shoot was represented by the value (°) measured between an N-1 shoot and an N-2 shoot. The angles of three primary branches and two secondary branches per tree were also measured. The primary branch angle was represented by the value (°) measured between a primary branch (second order axis) and the trunk (first order axis), whereas the secondary branch angle was represented by the value (°) measured between a secondary branch (third order axis) and primary branch. Total numbers of angles measured on the primary and secondary branches were 75 and 150, respectively. The shoot diameter was measured in millimetres at its base using a beak-shaped measuring tool. Flowering shoots were determined according to the presence of mixed buds (on the terminal, subterminal or lateral position). In 1-year-old shoots, the number of vegetative and mixed buds was determined, as well as the number of female flowers per inflorescence.
All parameters, except buds and flowers, were measured during winter dormancy. The fruit-bearing type was determined twice in a growing season: first in winter when shoots displayed visible scars of the previous year fruits, and then in spring during flowering.
The effects of morphotype on individual traits were evaluated by ANOVA, and the Duncan multiple-range test (DMRT) at P 
0·05 in the statistical programming package STATISTICA for Windows (Tulsa, OK, USA, 1994).
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSLITERATURE CITED |
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Qualitative analysis of tree architecture: determination of morphotypes
Passing through the orchard, 80 schemes were created in situ after accurate observations of the trees. They represented various types of branching and fruit-bearing patterns on the level of the structural unit ‘a 2-year-old shoot with corresponding 1-year-old shoot’. Some of the schemes are presented in Fig. 1.
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Of the 80 schemes defined in the spring of 1998, four were chosen as the most typical and frequent representatives of certain branching and fruiting types in the whole population. They were referred to as morphotypes and labelled from I to IV (Fig. 2).
Morphotype I exhibits a strong acrotony. Branching pattern is sparse and growth units are long. In addition to monocyclic shoots, there are also bicyclic ones, and on the branches in the canopy top there are even tricyclic vegetative shoots. The determinate growth is typical of annual shoots growing on 2-year-old and older shoots. Flowering buds can only be found in the terminal position on the axis of annual shoots.
Morphotype II has mesotonic branching. Branching is more dense than in morphotype I. Growth units are of medium length. Determinate growth can be present on secondary branches (third order axis), and on annual monocyclic shoots growing on 2-year-old shoots. Fruiting shoots are in terminal and sub-terminal positions.
In morphotype III, acrotony of the shoots can be seen as in morphotype I. However, the number of axillary shoots in type III is higher. Branching is mesotonic on the upper half of the shoot and growth units are medium to long. Terminal buds on the second and third order axes often start to rest or die. Determinate growth is developed on annual monocyclic shoots on 2-year-old shoots. Terminal and sub-terminal shoots bear fruits. Vegetative shoots can also be bicyclic.
Morphotype IV develops dense branching with medium to short growth units. Primary branches (second order axis) have a determinate growth, as well as axillary annual shoots, on the 2- and 3-year-old shoots. Flowering buds are found in terminal, sub-terminal and lateral positions on the annual shoots.
Quantitative analysis of a fruiting branch
Length of monocyclic shoots.
A three-year-old shoot (N-2) is the longest (80 cm) in intermediate type III, with acrotonic branching, and the shortest (57 cm) in lateral type IV (Table 2). The intermediate type II with mesotonic branching has slightly shorter N-2 shoots (79 cm) than type III. In genotypes that belong to type I, 3-year-old bearers are of medium length (69 cm).
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Two-year-old shoots (N-1) are the longest in types III (28 cm) and II (27 cm) (Table 2). The shortest (N-1) shoots are measured in type IV (23·7 cm). They are slightly longer in type I (24·1 cm). Differences are not statistically significant.
Morphotypes do not differ significantly in the length of 1-year-old shoots (N): the shortest N shoots are measured in type II (19 cm) (Table 2), followed by types I (22 cm), IV (23 cm) and III (24 cm).
The cumulative length of 3-, 2- and 1-year-old wood was greatest in types II (387 cm) and III (380 cm), followed by type I (275 cm). The shortest cumulative length (253 cm) was recorded in type IV (Fig. 3).
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Number of nodes.
Two-year-old shoots (N-1) have more nodes (8·4) in type IV (Table 2). Types III and II have 7 and 7·1 nodes, respectively, whereas type I has 7·2 nodes per shoot.
One-year-old shoots (N) show statistically significant differences between morphotypes regarding the numbers of nodes per shoot. Type I exhibits the lowest number of nodes (6·9) (Table 2), this being slightly higher in type II (7·1). In types IV and III, the number of nodes is significantly higher (9·1 and 9·3).
Total number of 2-year-old shoots (N-1) and 1-year-old shoots (N) on the 3-year-old basis (N-2).
In type IV, the fruiting branch consists of 4·9 N-1 shoots, which is significantly less than in types II and III (respectively, 7·6 and 6·9), and similar to type I (5·2). Concerning the number of N shoots, the relationship among the morphotypes is almost the same: in types IV and I, 3·5 and 3·6 N shoots were observed, compared with types II and III, where 5·8 and 4·7 N shoots developed on average.
Number of flowering 2-year-old shoots (N-1) and 1-year-old shoots (N).
The lowest number of flowering (N-1) shoots is observed in type I (1·0); this is significantly lower than that observed in other morphotypes. Type IV has 2·9 N-1 fruiting shoots, while in types III and II, fruits develop on 3·3 and 3·7 N-1 flowering shoots (Table 2). The number of flowering N shoots is significantly lower in type I (0·4). Types III and II have 3·0 and 3·2 fruiting N shoots, and the lateral genotypes have significantly more fruiting 1-year-old shoots (2·6).
Angles.
Primary branches (second order axis) in type IV are most widely spread (Table 2). Their angles do not differ appreciably (Fig. 4A). In type II, the angles of primary branches are the most heterogeneous. Angles are widest (82 °) in type I, and narrowest (40 °) in type III. The most erect primary branches are found in type I.
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Secondary branches (third order axes) have similar angles irrespective of the morphotype, ranging from 51·5 ° (type II) to 55·3 ° (type IV) (Table 2; Fig. 4B). The angles in type II are the most homogeneous. The absolute minimum is found in type III (40 °) and the maximum (67 °) in type IV.
Two-year-old shoots (N-1) are most widely spread in type III (49·3 °) (Table 2; Fig. 4C), followed by types IV and II (46·8 and 46·9 °). The most erect shoots are found in type I (44·3 °), where the absolute minimum angle is recorded (23 °).
Angles of 1-year-old shoots (N) are wider in types III and II (46 and 44 °) than in types IV and I (41·9 ° and 38·7 °; Table 2; Fig. 4D). The homogeneity of measurements within each morphotype is highest in type IV. Homogeneity of measured angles is lowest in type II, in which the most erect 1-year-old shoot was measured (82 °).
Basal diameter.
Two-year-old shoots (N-1) in type IV have a significantly larger basal diameter (10·8 mm) than other types. Types II and III have N-1 shoots with the same diameter (9·3 mm) and type I has the thinnest N-1 shoots (8·8 mm) (Table 2). One-year-old shoots (N) are significantly thicker in type IV than in the other types, with the difference ranging from 1·7 mm (for type III) to 2·1 mm (for type II) (Table 2).
Numbers of buds and flowers on 1-year-old (N) shoots
Vegetative buds.
In morphotype I there are, on average, 4·9 vegetative buds (Table 2). Type III has 4·8, and type II has 4·3 vegetative buds per shoot. Type IV has only 3·1 vegetative buds per shoot.
Mixed (flowering) buds.
The 1-year-old shoots of type IV have 1·7 mixed buds per shoot (Table 2). Usually, there are three flowering axillary buds plus a flowering terminal bud; sometimes the terminal bud has aborted and four axillary buds have developed fruits. Type III has 1·2 mixed buds per shoot. Usually, there is the flowering terminal bud plus zero to four axillary buds. Type II has 1·1 mixed buds per shoot. Terminal buds plus zero to three axillary buds bear fruits. In type I, fruits can develop only from one (terminal) bud.
Number of female inflorescences per fruiting 1-year-old shoot
Types I and II exhibit 1·9 female inflorescences per shoot (Table 2). In type I, one to three inflorescences are developed from one (terminal) bud. In type II, one to four inflorescences are developed from a terminal bud. The highest total number of female inflorescences per shoot is eight, as the inflorescences are also developed from the flowering sub-terminal bud or axillary buds. On average, type III has two female inflorescences per shoot. One or two of these have developed from the terminal bud, but flowering sub-terminal buds and axillary buds on the 1-year-old shoot are also important. Type IV bears, on average, three female inflorescences per shoot. The highest possible number of developed female inflorescences is nine. If the terminal bud is present, it can lead to the development of one or two inflorescences; other inflorescences develop from axillary buds. If the terminal bud has died, all female inflorescences develop from the flowering axillary buds.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSLITERATURE CITED |
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We have shown that the connection between the architecture of walnut trees and their generative and vegetative potential can be described using architectonic decomposition and quantitative analysis of their individual constituents.
Architectural analysis of a large number of freely growing Slovenian walnut progenies has illustrated the great genetic variability with regard to both the topological organization of constituents (branching pattern and the composition of the botanical entities) and the geometrical organization (spatial arrangement, orientation, size and shape of constituents) of the trees.
The characteristics of the architectural unit of walnut trees, which represent, according to Barthélémy and Caraglio (1991), all the different categories of tree axes and the varying ways these axes develop, have been analysed. They are given in Table 1, together with the architectural scheme which describes the basic structure of Juglans regia L. A similar breakdown for Fraxinus L. is given by Caraglio et al. (1998).
The growth unit and characteristics of 1-year-old shoots were described. Factors that affect the number of growth units are: genotype vigour, fruit-bearing habit, position of the shoot inside the tree crown and the shoot angle. Three types of shoots (monocyclic, bicyclic and tricyclic) were found, in agreement with Mauget (1976), Barthélémy et al. (1995), Sabatier et al. (1995), Ducousso et al. (1995) and Sabatier and Barthélémy (2001). The majority of 1-year-old shoots was monocyclic (formed from one growth unit). They could be floriferous (usually on terminal position Barthélémy et al., 1995) or vegetative. Bicyclic shoots were found mainly in very vigorous genotypes. They were mostly vegetative. Barthélémy et al. (1995) also report that bicyclic shoots in walnut are usually vegetative. They were identified by the median zone of long cataphylls (i.e. scaly leaves) connected to noticeable short internodes which separate spring and summer growth flushes (Sabatier and Barthélémy, 2001). Tricyclic shoots with two rings of cataphyll scars and short internodes, which represent two resting phases of extension, were seldom found. Two distinctive phases, a stagnant growth phase and a vigorous extension-growth phase, distinguished from each other by morphological traits, were detected in the shoot growth of a deciduous tree, Acanthopanax sciadophylloides Franch. Et Savat. by Seino (2001). Puntieri et al. (2000) also reported preformed and neoformed shoots in Nothofagus dombei (Mirb.) Blume.
For quantitative research of fruit-bearing branches in walnut trees, a 3-year-old shoot with its corresponding 2-year-old and 1-year-old shoots was chosen as a structural unit for carrying out morphometric analyses. Shoots were researched in detail in four different morphological types (morphotypes). Results indicate that morphotype I exhibits poor generative potential. On the 3-year-old branch, only every fifth 2-year-old shoot and only every tenth 1-year-old shoot has the ability to bear fruit. There is always only one flowering bud. On average, 1·9 female inflorescences develop from this bud. In this morphotype, primary branches as well as 2-year-old and 1-year-old shoots form more erect angles than in the other three types. This characteristic can worsen the differentiation of flowering buds in terminal fruit-bearing walnuts. On the other hand, their growth potential is better, as demonstrated by the high growth ratio (the ratio between shoot length and its basal diameter) in 1-year-old shoots, and by the number of vegetative buds on shoots, and also by the length of shoots.
The number of vegetative and fruiting shoots in walnut was investigated previously by Ducousso et al. (1995). Terminal, intermediate and lateral fruit-bearing cultivars of French and American origin were included in the analyses. It was stated, when comparing the terminal-fruiting cultivar Soleze with the lateral-fruiting one, Lara, that the fruiting branch in Soleze has fewer flowering 1-year-old shoots compared with Lara, while the number of vegetative shoots is higher in Soleze. The authors concluded that terminal fruit-bearing walnuts do not tend to have a high crop but can regenerate very well. On the other hand, the lateral fruit-bearing walnuts are more capable of flowering and possess a low ability to regenerate. The great generative potential of the lateral-fruiting walnuts was also reported by Germain (1990) and McGranahan and Leslie (1991).
In this study, the good fruit-bearing potential of morphotype IV is determined by the ratio between the number of flowering shoots and the total number of shoots. The ratios in 2-year-old and 1-year-old shoots are 0·59 and 0·74, respectively. On average, there are 1·7 generative buds per 1-year-old shoot and three female inflorescences per mixed bud. In addition, lateral-fruiting genotypes have thicker shoots than other types. Increasing thickness of shoots is associated with increasing hydraulic conductivity (Cochard, 1992) in various species. Thick shoots are therefore more likely to be able to support a heavy fruit load and to allow an appropriate nutrient and water supply to the fruit, thus favouring higher fruit quality (Génard and Bruchou, 1992). Lateral-fruiting walnuts are therefore expected to have large fruits with a better kernel quality than the fruits of other types. This conclusion differs from that of Lauri et al. (2001), who postulated that lateral-bearing walnuts show a tendency to bear nuts of decreasing size from year to year. Nevertheless, the good generative potential of morphotype IV is reflected in the short juvenile period. It is known that the Slovenian lateral walnuts bear fruit in the fifth or sixth year after planting, but in other fruiting types the juvenile period can last for more than 7–12 years (Solar et al., 2001, 2002).
The poor vegetative potential of lateral walnuts is likely to be attributable to the length and number of shoots, their low growth potential, the small total number of 2-year-old and 1-year-old shoots, and the small number of vegetative buds on 1-year-old shoots. Three-year-old bearers are shortest and 2-year-old shoots are shorter than those in other morphotypes.
The growth and ability to bear fruit are more balanced in the intermediate morphotypes II and III. In both types, 48 % of 2-year-old shoots flower, as do 55 and 65 % of 1-year-old shoots on fruiting branches. On average, 1·1 generative buds and 1·9 and 2·0 female flowers develop on 1-year-old shoots. Both types develop 3-year-old and 2-year-old shoots that are longer than those of morphotypes I and IV. In 2-year-old shoots, they also have longer internodes and a better growth ratio. The acrotonic intermediate type also has the longest 1-year-old shoots with the best ratio between lengths and basal diameter. The great vegetative potential of intermediate fruit-bearing walnuts can also be seen in Fig. 3. In these morphotypes, cumulative lengths of 3-, 2- and 1-year-old shoots are 28 % bigger than in the type I and 34 % bigger when compared with the type IV. According to Bell (1991), long shoots with long internodes and well distributed leaves are often considered to exhibit an exploratory capacity, i.e. extending the framework of the plant into new territory. Such a definition can apply to walnut with intermediate fruit-bearing type which, according to the findings of our research, exhibit a good ability to regenerate and self-regulate growth and regeneration.
Interestingly, the angles measured in this study indicate that, in general, primary branches are more widely separated than secondary ones. The 2-year-old shoots also exhibit larger angles than the corresponding 1-year-old shoots. In general, the present results show that higher order axes form wider angles compared with axes of lower orders, and this is true for all morphotypes investigated.
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSLITERATURE CITED |
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This investigation has so far enabled us to define the connection between the most typical morphological walnut types and their capacity to grow and bear fruits, which facilitates evaluation of their horticultural value. However, to achieve a thorough understanding of this value, analysis of the functioning of flowering shoots on fruiting branches must be carried out, extending over a period of several successive years. In addition, research is needed to determine the genetic variability of tree structure and to study the link between tree architecture and ecophysiological processes (the influence of light, mineral nutrition, hormones, etc.), agrotechnical measures (pruning, bending, thinning, etc.) and climatic conditions. Such information would be useful in orchard management (Sabatier and Barthélémy, 2001). According to Laurens et al. (1998) and Solar et al. (2003), long-term analysis of tree architecture and the architecture of the fruit-bearing branch in particular, could help to identify early morphological markers of various phases of ontogenesis and could identify new markers for use in walnut breeding schemes.
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ACKNOWLEDGEMENT |
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We thank Dr Pierre Eric Lauri (Fruit Arboriculture Laboratory, INRA Montpellier, France) for his pre-review and comments.
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LITERATURE CITED |
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Barthélémy D, Caraglio Y. 1991. Modélisation et simulation de l’architecture des arbres. Forêt-entreprise 73: 28–39.
Barthélémy D, Edelin C, Hallé F. 1991. Canopy architecture. In: Raghavendra AS, eds. Physiology of trees. John Wiley and Sons.
Barthélémy D, Sabatier S, Pascal O. 1995. Le développement architectural du noyer commun, Juglans regia L. (Juglandaceae). Forêt-entreprise 103(3–4): 61–68.
Bell AD. 1991. Plant form. An illustrated guide to flowering plant morphology. Oxford, New York, Tokyo: Oxford University Press.
Bernhard R. 1961. Mise a fleur et alternance chez les arbres fruitièrs. Paris: INRA.
Caraglio Y, Barthélémy D. 1997. Revue critique des terms relatifs à la croissance et à la ramification des tiges des végétaux vasculaires. In: Bouchon J, Reffye de P, Barthélémy D, eds. Modélisation et simulation de l’architecture des plantes. Paris: INRA Editions. Science Update, 11–87.
Caraglio Y, Godin C, Costes E, Barthélémy D. 1998. Mesure et represéntation des plantes. In: Architecture et Modélisation en Arboriculture Fruitière. 11eme Colloque sur les Recherches Fruitières INRA – Ctifl. Montpellier, France, 5–6 Mar. 1998, 22–32.
Cochard H. 1992. Vulnerability of several conifers to air metabolism. Tree Physiology 11: 73–83.[Abstract]
Denffer D, Ziegler H. 1988. Morfologija I fiziologija. Ud
benik botanike za visoke 
kole. Zagreb: kolska knjiga (cro.).
Ducousso I, Sabatier S, Barthélémy D, Germain E. 1995. Comparison de quelques caracteristiques morphologiques des pousses annuelles et des branches de la cime de sept variétés de Noyer commun, Juglans regia L. (Juglandaceae). In: Les Coloques, No. 74. Colloque Architecture des arbres fruitières et forestières. Montpellier, France, 23–25 Nov. 1993, 91–108.
Génard M, Bruchou C. 1992. Multivariate analysis of within-tree factors accounting for the variation of peach fruit quality. Scientia Horticulturae 52: 37–51.[CrossRef]
Germain E. 1979. Création par hybridation, de variétes de Noyer (Juglans regia L.) associant une floraison tardive a une mise a fruit tres rapide et une productivite elevee. Expose d’une methode. Annals Amélioration des Plantes 29(2): 187–199.
Germain E. 1990. Inheritance of late leafing and lateral bud fruitfulness in walnut (Juglans regia L.), phenotypic correlations among some traits of the trees. Acta Horticulturae 284: 125–134.
Germain E. 1992. Le noyer. In: Gallais A, Bannerot H, eds. Améloration des especes végétales cultivées, objectifs et critères de sélection. Paris: INRA, 125–134.
Godin C, Guédon Y, Costes E. 1998. Éxploration et analyse de l’architecture des arbres fruitières. In: Architecture et Modelisation en Arboriculture Fruitière. 11eme Colloque sur les Recherches Fruitieres INRA – Ctifl. Montpellier, France, 5–6 Mar. 1998, 33–45.
Guédon Y, Barthélémy D, Caraglio Y, Costes E. 2001. Pattern analysis in branching and axillary flowering sequences. Journal of Theoretical Biology 212: 481–520.[CrossRef][Web of Science][Medline]
Hallé F, Oldeman RAA. 1970. Essai sur l’architecture et la dynamique de croissance des arbres tropicaux. Paris: Masson.
Hallé F, Oldemann RAA, Tomlinson PB. 1978. Tropical trees and forests: an architectural analysis. Berlin: Springer Verlag.
Jaeger M, de Reffye DE. 1992. Basic concepts of computer simulation of plant growth. Journal of Biosciences 17(3): 275–291.[CrossRef][Web of Science]
Kervella J, Pfeiffer F, Pages L, Genard M, Serra V. 1998. Taking into account relationships between ecophysiological processes in the breeding for peach tree characteristics. Acta Horticulturae 465: 145–154.
Laurens F, Audergon JM, Claverie J, Duval H, Germain E, Kervella J, Le Lezec M, Lespinasse JM. 1998. Variabilité génétique et prise en compte des caracteristiques de l’arbre dans les programmes d’amélioration génétique des espèces fruitières ligneuses à l’INRA. In: Architecture et Modélisation en Arboriculture Fruitière. 11eme Colloque sur les Recherches Fruitières INRA – Ctifl. Montpellier, France, 5–6 Mar. 1998, 110–124.
Lauri PE, Delort F, Germain E, Reynet P. 2001. Factors affecting nut weight in walnut (Juglans regia L.) – an analysis of genotypes with contrasting branching patterns. Acta Horticulturae 544: 265–273.
McGranahan G, Leslie C. 1991. Walnuts (Juglans). In: Moore JN, Ballington JR Jr, eds. Genetic resources of temperate fruit and nut crops, part 2. Wageningen, The Netherlands: International Society of Horticultural Sciences, 907–951.
Mauget JC. 1976. Croissance et ramification de la pousse de l’annee de jeunes noyers (Juglans regia L.). Physiologie Végétal 14(2): 215–232.
Oldeman RAA. 1974. L’architecture de la forêt guyanaise. Mémoire no. 73. Paris: Orstom.
Puntieri JG, Souza MS, Barthélémy D, Brion C, Nunez M, Mazzini C. 2000. Preformation, neoformation, and shoot structure in Nothofagus dombeyi (Nothofagaceae). Canadian Journal of Botany 78: 1044–1054.[CrossRef][Web of Science]
Sabatier SA, Barthélémy D. 2001. Annual shoot morphology and architecture in Persian walnut. Acta Horticulturae 544: 255–264.
Sabatier S, Barthélémy D, Ducousso I, Germain E. 1995. Nature de la pousse annuelle chez le Noyer commun, Juglans regia L. var. Lara (Juglandaceae): preformation hivernale et printaniere. In: Les Coloques, No. 74. Colloque Architecture des arbres fruitières et forestières. Montpellier, France, 23–25 Nov. 1993, 109–123.
Sabatier S, Barthélémy D, Ducousso I, Germain E. 1998. Modalités d’allongement et morphologie des pouses annuelles chez le noyer commun, Juglans regia L. ‘Lara’ (Juglandaceae). Canadian Journal of Botany 77: 1595–1603.[CrossRef]
Seino T. 2001. Differences in architecture and shoot growth during stagnant and extension growth phases of Acanthopanax sciadophylloides (Araliaceae). Annals of Botany 87: 347–354.
Solar A. 2000. Determination of morphometric and pomological indicators in walnut (Juglans regia L.) breeding. Doctoral thesis, University of Ljubljana, Biotechnical Faculty, 156 pp. (sl).
Solar A, Hudina M, tampar F. 2001. Relationship between tree architecture, phenological data and generative development in walnut (Juglans regia L.). Acta Horticulturae 544: 275–286.
Solar A, Ivan
i A, tampar F, Hudina M. 2002. Genetic resources for walnut (Juglans regia L.) improvement in Slovenia. Evaluation of the largest collection of local genotypes. Genetic Resources and Crop Evolution 49: 491–501.[CrossRef][Web of Science]
Solar A, Ivan
i A, tampar F. 2003. Morphometric characteristics of fruit bearing shoots in Persian walnut (Juglans regia L.) – potential selection criteria for breeding. European Journal of Horticultural Science 68: 86–92.[Web of Science]
Szentivanyi P. 1990. Breeding early fruiting, high producing walnut cultivars leafing after late spring frosts. Acta Horticulturae 284: 175–182.
Ustin SL, Martens SN, Vanderbilt VC. 1991. Canopy architecture of a walnut orchard. IEEE Transactions on Geoscience and Remote Sensing 29: 843–851.[CrossRef][Web of Science]
Wu RL, Hinckley TM. 2001. Phenotypic plasticity of sylleptic branching: genetic design of tree architecture. Critical Reviews in Plant Sciences 20: 467–485.[CrossRef][Web of Science]
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