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European Pear Architecture and Fruiting-Branch Management: Overview of an INRA Research Program P.E. Lauri and E. Costes A. Belouin Équipe Architecture et Fonctionnement des Station d’Amélioration des Espèces Espèces Ligneuses, INRA, UMR Biologie Fruitières et Ornementales, INRA, du Développement des Plantes Beaucouzé, France Pérennes Cultivées, Montpellier, France Keywords: morphological criteria, training systems, branching and fruiting patterns, sylleptic

branching, onset of return bloom, extinction, desynchronization, IFP Abstract

Tree architecture traits are often described in relation to planting densities, tree height or adaptation of the tree to mechanical pruning. The need to reduce both pruning costs and the use of plant growth regulators (PGRs), notably in a context of integrated fruit production (IFP), lends further support to the development of architectural analysis as an aim in itself. A research program at the Institut National de la Recherche Agronomique (INRA), France, is currently focusing on two main objectives: the optimisation of training methods based on natural tree habit and the definition of new morphological criteria to better meet the needs of breeders. Resistance to pests and diseases, along with fruit quality, is also a major consideration. Observations are being carried out on trees of four cultivars in order to determine and compare their branching and fruiting patterns. Natural tree behavior is being investigated at two different development stages. The development of laterals along the trunk and their number and location during the earliest years of growth have been studied as the main determinants of tree architecture. A relationship is highlighted for differences in sylleptic branching between the first and second year shoots and the onset of bloom in the third spring. Observations were then carried out on fruiting branches once the adult stage had been reached. A relationship is shown between high-return bloom and the physiological abortion, called extinction, of a certain number of young spurs. On the other hand ‘Angélys,’ a newly released INRA cultivar, shows that a high alternation ratio at the individual spurs may be offset by an improved balance between vegetative and flowering spurs, resulting in more regular flowering over subsequent years (desynchronization phenomenon). INTRODUCTION

European pear production ranks third in France among the major fruit crops (apple, peach and nectarine), with 290,000 t in 1999 (Agreste, 1999), and about 85% of output is situated in the South of France. Over the last two decades, plantation acreage has decreased by about half to 12,000 ha in 1999, whereas production has decreased by about one-third (Masseron and Trillot, 1991; Agreste, 1999). This reduction is mainly due to the lower profitability of pear compared to other fruits and high fire blight (Erwinia amylovora) susceptibility of the winter cultivar Passe Crassane. Although 30% of French orchards are more than 20 years old, new plantations are nevertheless in development with cultivars such as Williams (Summer), Conference, Doyenné du Comice (Autumn) and, more recently, the INRA (Institut National de la Recherche Agronomique; France) newly-released Angélys (Winter). Early production combined with high and regular mature orchard yields of good quality fruit is a major objective of these orchards.

Thirty years ago, Hermann (1970, 1971) showed that in comparison to three-bud pruning, long pruning in ‘Williams’ was more effective in reducing the time to initial bearing and increased fruit quality. This method has since been extended to mature trees of such other cultivars as Alexandrine Douillard, Guyot and Harrow Sweet with positive effects on yields, fruit size and economic profitability (Florens et al., 1998). In addition, although hybrids are not eliminated from breeding programs solely on the basis of morphological criteria, these

Proc.8th IS on Pear Eds. L. Corelli-Grappadelli et al. Acta Hort 596, ISHS 2002

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programs would benefit from the introduction of tree characteristics, in parallel with fruit characteristics and pest and disease resistance (Laurens et al., 2000). A research program at INRA is currently focusing on two main objectives: the optimization of training methods based on natural tree habit and the definition of new morphological criteria to better meet the needs of breeders. We report herein some of the preliminary studies carried out at whole-tree and fruiting-branch levels, and the results are discussed in terms of possible applications in tree training. MATERIALS AND METHODS

The studies were carried out on the three regular bearing cultivars Angélys, Conference, and Williams, and on the alternate bearing Doyenné du Comice. All the cultivars were grafted on BA29 at INRA’s Angers station in spring 1995. Young Tree Growth and Branching

The trees were described after the first and second year of growth after Costes et al. (1997) and Godin et al. (1997). The length, number of nodes (a node was counted when its corresponding axillary bud was visible to the naked eye and basal diameter of all the annual shoots (ASs) on the trunk and scaffold branches were recorded. The laterals were located according to the rank of their bearing node and sorted into four categories: (i) latent bud, (ii) short shoot (less than 5cm), (iii) medium shoot (or brindle, longer than 5 cm and shorter than 20 cm), (iv) long shoot (longer than 20 cm). The laterals were also sorted as sylleptic or delayed shoots depending on the period of their first development (Bell, 1991). The total number of flowering growth units was recorded for each tree in the spring of the third year. The analysis of the data focused initially on the number and the location of the long laterals along the main axes, then on the relationship between the vegetative development of the whole tree and the number of flower clusters initiated in the third spring. Fruiting-Branch Analysis

Long laterals along the trunk were the subject of supplementary analysis. Here, ten four-year-old unpruned fruiting branches of approximately the same basal diameter and silhouette, and situated at breast level, were analysed in spring 1999 and 2000 after the methodology proposed for apple by Lauri et al. (1995, 1997). This method was used to chart the development of each lateral (vegetative, flowering/fruiting, latent, dead) over the four year study. RESULTS AND DISCUSSION Young Tree Growth and Branching

In the first year of growth, ‘Conference’, ‘D. du Comice’ and ‘Williams’ showed a similar mean number of nodes per AS whereas Angélys had a significantly lower value (Table 1). In the second year, mean node number remained comparable for ‘Conference’ and ‘Williams’, but was substantially modified for ‘Comice’ and ‘Angélys’, the former’s increasing and the latter’s decreasing.

Percentages of branching nodes were similar in ‘Conference’ and ‘Angélys’, and in ‘Comice’ and ‘Williams’ over the first year of growth, although the latter two showed a higher percentage of branching nodes (about 90%). In the second year, ‘Williams’ was characterized by a marked decrease in the percentage of branching nodes (resulting from a substantial decrease in the number of immediate laterals, data not shown), while ‘Angélys’, ‘Conference’ and ‘Comice’ showed less than a 10% variation between the two successive years. All the cultivars bore more than 10 long laterals along the first AS, though very few of these developed sylleptically (Fig. 1). Thus, under our study conditions, all the trees developed a sufficient number of long laterals to allow young tree training. Here again ‘Comice’ exhibited a high level of vegetative development, with many long laterals continuing to develop along the second AS.

In the third year, ‘Williams’ was the only cultivar to develop a significantly higher

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number of flower clusters per tree (Tab. 1). ‘Comice’ and ‘Conference’ had a low number of flower clusters and a high level of vegetative growth, whereas the low number of flower clusters on ‘Angélys’ was more surprising given its weak vigor. These results suggested that the onset of bloom may be related to differences in branching (Tab. 1), particularly sylleptic branching, between year one and two. This was confirmed by the existence of a linear relationship (r² = 0.91) between this differential in sylleptic branching and the total number of flower clusters per tree in the third year (using a larger set of cultivars, data not shown). Fruiting Branch Level

‘Conference’ and ‘Williams’ were marked by a significant reduction in lateral number (39% and 28%, respectively; Tab. 2) between 1- and 4-year wood, whereas the number of laterals did not vary significantly for ‘Angélys’ and ‘Comice’ (12% and 2%, respectively; Tab. 2). This phenomenon resulted mainly from the abortion of flowering laterals (data not shown) and has been described as the extinction phenomenon in apple (Tab. 2; Lauri et al., 1995). Conversely, return bloom in individual spurs was high for ‘Williams’ and ‘Conference’ between 1- and 2-year wood as well as between 2- and 3-year wood, whereas it was low for ‘Comice’ and ‘Angélys’ between 2- and 3-year wood (Tab. 3).

Figure 2 shows that ‘Comice’ and ‘Angélys’, characterized by the stronger alternating behaviour at the spur level, presented two different flowering and fruit-set patterns. Both cultivars showed a low flowering ratio on 1-year wood and a high one on 2-year wood. In ‘Comice’, the flowering ratio remained high irrespective of wood age and was associated with low fruit-set. In ‘Angélys’, the flowering ratio was lower on 3- and 4-year wood, with a higher fruit-set. CONCLUSIONS

The yield models reported by Sansavini and Musacchi (1994) underlined the link between the specific behaviour of each cultivar and the pruning method to be adopted. Our results show that complementary variables should be further defined at both the young-tree and fruiting-branch levels. At the young-tree level, the differential in sylleptic branching would appear to be an accurate predictor of the time at which a given cultivar will enter production. In addition, a high percentage of branching nodes over the first two years of growth, as observed with ‘Comice’, may be indicative of a risk of alternate bearing at the adult stage.

Three variables should be further defined at the fruiting-branch level: extinction, return bloom on the individual laterals and balance between flowering and vegetative laterals. The higher extinction values observed for the regular bearing cultivars Conference and Williams and the low extinction observed for the alternate-bearing ‘Comice’ suggest a more general negative relationship between the number of flowering spurs and the tendency to flower year after year on the same spur. These findings led us to test the thinning of spurs on spur-bound alternating cultivars such as Comice. Preliminary studies (Lauri et al., 1998) showed that long pruning, associated with the removal of 25% to 50% of the spurs, resulted in an increase in bourse-over-bourse and fruit-set. This method was also found to alleviate spur crowding in the tree canopy, leading to larger fruit size in cultivars like Alexandrine Douillard, Guyot and Harrow Sweet (Florens et al., 1998).

Despite its known regular bearing (Le Lezec and Belouin, 1999), ‘Angélys’ had low values for extinction and return bloom at individual spurs that were similar to those noted with D. du Comice. Each cultivar has a specific fruiting strategy, which includes both the cultivar-specific flowering ratio and the subsequent relationships between the number of inflorescences and fruit-set (Helsen and Deckers, 1984). ‘Comice’ has a tendency to synchronize flowering of the laterals with a high flowering ratio (between 1/2 and 2/3) and a low fruit-set. By contrast, Angélys has a tendency to desynchronise flowering of the laterals with low flowering ratio (less than 1/3) on 3- and 4-year-old wood, resulting in a better balance between vegetative and flowering spurs and a higher fruit-set.

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Literature Cited Agreste. 1999. La statistique agricole. n° 5, septembre. Ed. Ministère de l'agriculture et de la

pêche. Paris. Bell, A.D. 1991. Plant Form. An illustrated guide to Flowering Plant morphology. Oxford

University Press. Costes, E., Godin, C. and Guédon, Y. 1997. A methodology for the exploration of fruit tree

structures. Acta Hort. 451(2):709-716. Florens, B., Montagnon, J.M., Ricavy, I., Chabrière, C. and Reynier, C. 1998. Poirier-Intérêt

de la taille longue. Réussir Fruits et Légumes, 169:62 - 64. Godin, C., Guédon, Y., Costes, E. and Caraglio, Y. 1997. Measuring and analyzing plants

with the AMAPmod software. In Michalewicz M. ed., Advances in computational life science. Vol. I Plants to ecosystems, Chapter 4, CSIRO, Australia.

Helsen, J. and Deckers, J.C. 1984. Fruit set and growth reactions of pear trees, cv. Doyenné du Comice on Quince A, pruned at different ratios of vegetative on generative buds. Acta Hort. 149:145-152.

Hermann, L. 1970. Analyse des effets de deux méthodes de taille sur la croissance et la production de la variété de poirier Williams. I. L'Arboriculture Fruitière. 201:23-25.

Hermann, L. 1971. Analyse des effets de deux méthodes de taille sur la croissance et la production de la variété de poirier Williams. II. L'Arboriculture Fruitière 202:24-29.

Laurens, F., Audergon, J.M., Claverie, J., Duval, H., Germain, É., Kervella, J., Lelezec, M., Lauri, P.É. and Lespinasse, J.M. 2000. Integration of architectural types in French programmes of ligneous fruit species genetic improvement, Fruits 55:141-152.

Lauri, P.É., Térouanne, É., Lespinasse, J.M., Regnard, J.L. and Kelner, J.J. 1995. Genotypic differences in the axillary bud growth and fruiting pattern of apple fruiting branches over several years. An approach to regulation of fruit bearing. Sci. Hort. 64:265-281.

Lauri, P.É., Lespinasse, J.M. and Térouanne, É. 1997. Relationship between the early development of apple fruiting branches and the regularity of bearing. An approach to the strategies of various cultivars. J. Hort. Sci. 72:519-530.

Lauri, P.E., Belouin, A., Le Lezec, M., 1998. Contrôle de la fructification de la branche fruitière du poirier (Pyrus communis L.) cv Doyenne du Comice, par la réalisation d’extinction manuelle: quelques résultats préliminaires. 11ème colloque INRA-Ctifl sur les Recherches Fruitières: Architecture et Modélisation en Arboriculture Fruitière. Montpellier (France) 5-6 ,mars 1998, pp. 208-213.

Le Lezec, M., Belouin, A. 1999. Poire–Angélys, une nouvelle variété. Réussir Fruits et Légumes 180:46-47.

Masseron, A. and Trillot, M. 1991. Le Poirier. Ctifl. Paris. Sansavini, S. and Musacchi, S. 1994. Canopy architecture, training and pruning in the

modern European pear orchards: an overview. Acta Hort. 367:152-172.

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Tables Table 1. Mean number of nodes and number of laterals per annual shoot (AS), mean

percentage of branching nodes per AS and differential values (1) over the first two years of growth.

Number of nodes

per AS Year effect

Number and % of Laterals per AS

Year effect

% diff.

Number flower

cluster per tree

1st year 2nd year 1st year 2nd year 3rd year Angélys 32.1 b1 10.9 c * 20.7 c 64 8.0 d 73 * +9 31.7

Conference 44.5 a 46.4 a ns 29.7 b 69 29.3 b 63 ns -6 28.3 Comice 38.3 ab 51.3 a * 34.8 ab 91 41.9 a 82 * -9 31.0

Williams 41.7 a 38.3 b * 38.3 a 92 18.9 c 49 * -43 130.6 1Mean separation according to Newman-Keuls multiple range test. Numbers followed by the same letter within the same column, or ns within the same line, are not different at the 5% level. Table 2. Variation in the percentage of laterals (number of vegetative and flowering laterals

over the total number of nodes on the branch) between 1- (1-Y-O W) and 4- (4-Y-O W) year-old wood, and extinction (difference between percentage of laterals on 1- and 4-Y-O W) for the four cultivars.

Wood Age Cultivar 1-Y-O W 4-Y-O W Extinction

Angélys 66 54 12 b* Conference 81 42 39 a Comice 81 79 2 b Williams 66 38 28 a Mean separation according to Newman-Keuls multiple range test. Numbers followed by the same letter within the same column are not different at the 5% level. Table 3. Return bloom on individual spurs between 1- and 2-year-old wood (1-2), and 2- and

3-year-old wood (2-3), for the four cultivars. Results are expressed as mean percentage of the number of flowering laterals in year N+1 which flowered in year N over the total number of flowering laterals in year N.

Transition Cultivar 1-2 2-3 Angélys ----* 11 b Conference 21 a** 29 ab Comice ---- 19 b Williams 36 a 49 a * Almost no flowering on 1-year-old wood for ‘Angélys’ and ‘Comice’. ** Mean separation according to Newman-Keuls multiple range test. Numbers followed by the same letter within the same column are not different at the 5% level.

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Figures

Fig. 1. Comparison of the mean number of nodes of one-year old shoots on four pear

cultivars. Branching zones are indicated by hatched blocks whose position corresponds to ranks of nodes bearing a lateral and whose length is proportional to the mean number of nodes of the zone. For each zone, the mean number of long laterals is indicated nearby with the mean number of sylleptic long laterals between brackets.

Fig. 2. Variation in the percentage of flowering (closed symbols; ratio of the number of

flowering laterals to the total number of laterals) and fruit-set (open symbols; ratio of the number of fruitful inflorescences to the total number of inflorescences) on 1- to 4-year-old wood, for ‘Angélys’ and ‘Comice’.

90

80

70

60

50

40

30

20

10

0

11 b(0.1)

2.5 b

Angélys D. Comice Williams

10.2 b(0.1)

17.2 a(0.75)

14.7 a(0.35)

Conférence

13 b(0.38)

2.8 b(2.62) 3.4 b

(0.1)Cumulated

no

of

nodes

0

10

20

30

40

50

60

70

1 2 3 4

wood age

flow

erin

g / f

ruit-

set (

%)

AngélysDoyenné du ComiceAngélysDoyenné du Comice