Advances in Mass Clonal Propagation of Eucalyptus Urophylla X E. Grandis

BOIS ET FORÊTS DES TROPIQUES, 2008, N° 297 (3) GESTION DE LA RESSOURCE 15 EUCALYPTUS UROPHYLLA X E. GRANDIS

Advances in mass clonal propagation of Eucalyptus urophylla x E. grandis

R. A. Saya1 F. Mankessi1 in Congo M. Toto1 J.-N. Marien2 O. Monteuuis3

1 UR2PI BP 1291 Pointe-Noire Congo 2 CIRAD-UR2PI BP 1291 Pointe-Noire Congo 3 CIRAD-BIOS, UPR 39, TA A-39/C 34398 Montpellier Cedex 5 France

The advantages of the new technique developed for efficiently propagating by rooted cuttings E. urophylla x E. grandis artificial clones in Pointe Noire, Congo, are obvious: higher rooting rates, better overall quality of the cutting-issued plants produced in much shorter delays with easier and cheaper maintenance. At the research level, the quality and reliability of the field clonal tests established from such rooted cuttings are greatly improved while the time needed for wise clonal selection and for effective genetic improvement can be considerably shortened.

Large scale propagation of Eucalyptus urophylla x E. grandis clones using intensively managed container-grown stock plants in Eucalyptus Fibre Congo (EFC) facilities, Pointe Noire, Congo. Photo O. Monteuuis. BOIS ET FORÊTS DES TROPIQUES, 2008, N° 297 (3) 16 RESOURCE MANAGEMENT EUCALYPTUS UROPHYLLA X E. GRANDIS R. A. Saya, F. Mankessi, M. Toto, J.-N. Marien, O. Monteuuis

RÉSUMÉ ABSTRACT RESUMEN

NOUVELLE TECHNIQUE DE ADVANCES IN MASS CLONAL NUEVA TÉCNICA DE PROPAGACIÓN PROPAGATION CLONALE PROPAGATION OF EUCALYPTUS CLONAL INDUSTRIAL PARA LOS INDUSTRIELLE POUR LES UROPHYLLA X E. GRANDIS IN CONGO EUCALYPTUS UROPHYLLA EUCALYPTUS UROPHYLLA X E. GRANDIS EN EL CONGO X E. GRANDIS AU CONGO

La technique mise au point en 1978 à The basic technique developed in La técnica puesta a punto en 1978 en Pointe-Noire, au Congo, pour bouturer Pointe Noire, Congo, since 1978 for Pointe Noire, Congo, para la propaga- les clones d’eucalyptus hybrides natu- propagating by cuttings the natural ción por estacas de los clones de euca- rels Eucalyptus PF1 et E. 12 ABL x E. sali- Eucalyptus PF1 and E. 12 ABL x lipto híbridos naturales Eucalyptus PF1 gna s’est avérée inadaptée au boutu- E. saligna hybrid clones did not y E. 12 ABL x E. saligna se reveló ina- rage des hybrides artificiels E. urophyla worked satisfactorily on the E. uro- daptada para el estaquillado de los x E. grandis. En effet, seule une faible phylla x E. grandis artificial hybrid híbridos artificiales E. urophyla x E. proportion des pousses récoltées sur clones. Only a small proportion of the grandis. En efecto, sólo una pequeña les souches au champ après abattage cuttings collected from the field cop- proporción de vástagos, cosechados et utilisées comme pieds mères exten- picing stumps used as extensive stock en las cepas en el campo tras apeo y sifs s’enracinait. Les boutures difficile- plants could be rooted. Moreover, the empleados como plantas madre exten- ment produites montraient en outre resulting plants demonstrated an sivas, lograba arraigarse. Las estacas, une grande variabilité intraclonale qui unexpectedly high within clone vari- de difícil producción, mostraban ade- s’avérait préjudiciable non seulement à ability detrimental to final crop quality más una gran variabilidad intraclonal la qualité mais aussi à la productivité and yield. Replacing such stump- que perjudica la calidad y productivi- des plantations résultantes. Le fait de derived stock plants by intensively dad de las plantaciones resultantes. El remplacer les souches utilisées comme managed container-grown ones hecho de sustituir las cepas utilizadas pieds mères par des pieds mères véri- resulted in a noticeable enhancement como plantas madre por verdaderas tables cultivés de façon intensive en of cutting capacity for adventitious plantas madre, cultivadas intensiva- conteneurs permit d’améliorer considé- rooting as well as of the overall quality mente en contenedores, permitió rablement la capacité au bouturage des of the plants produced in much mejorar considerablemente la capaci- nouveaux clones hybrides artificiels, shorter delays with easier and dad de estaquillado de los nuevos clo- ainsi que la qualité des boutures pro- cheaper maintenance. The relevant nes híbridos artificiales, así como la duites plus rapidement et à moindre advantages of this new technique are calidad de las estacas, de producción coût.Les avantages de cette nouvelle obvious. At the research level, the más rápida y barata. Las ventajas de technique sont manifestes. En matière quality and reliability of the field esta nueva técnica son evidentes. En lo de recherche, la qualité et la fiabilité clonal tests established from such relativo a la investigación, la calidad y des tests clonaux établis à partir de ces rooted cuttings are greatly improved fiabilidad de las pruebas clonales nouvelles boutures ont pu être grande- while the time needed for wise clonal desarrolladas a partir de estas nuevas ment améliorées, permettant de sélec- selection and for effective genetic estacas se pudieron mejorar bastante, tionner les nouveaux clones de façon improvement can be considerably esto permitió seleccionar los nuevos plus rigoureuse dans des délais plus shortened. The benefits are even clones de forma más rigurosa y con courts pour le plus grand profit de greater for big scale operations, such plazos más cortos, favoreciendo así el l’amélioration génétique. Les bénéfices as mass production of clonal offspring mejoramiento genético. Los beneficios sont encore plus flagrants sur le plan for large size clonal plantations of uni- son aún más patentes a nivel operativo opérationnel pour la production effi- form superior quality. These aspects para la producción eficiente, a escala ciente à l’échelle industrielle de bou- are argued in the current paper, focus- industrial, de estacas de calidad supe- tures destinées à alimenter des planta- ing on the particularities of the new rior y homogénea para abastecer plan- tions clonales d’envergure, de qualité technique developed for efficiently taciones clonales de importancia, supérieure et homogène, tout en garan- mass producing by rooted cuttings garantizando al mismo tiempo una ele- tissant une forte productivité. Ces E. urophylla x E. grandis clones. vada productividad. Estos aspectos se aspects sont discutés dans cet article, analizan en este artículo, centrado en axé sur les particularités de cette nou- Keywords: adventitious rooting, las peculiaridades de esta nueva téc- velle technique de bouturage industriel cloning, container-grown stock plant, nica de estaquillado industrial de los des clones d’E. urophylla x E. grandis. eucalypt, mass clonal propagation, clones de E. urophylla x E. grandis. rooted cutting, stock plant manage- Mots-clés : bouture, clonage, enraci- ment. Palabras clave: estaca, clonación, nement adventif, eucalyptus, gestion enraizamiento adventicio, eucalipto, des pieds mères, pied mère hors-sol, manejo de plantas madre, planta propagation clonale industrielle. madre sin tierra, propagación clonal industrial. BOIS ET FORÊTS DES TROPIQUES, 2008, N° 297 (3) GESTION DE LA RESSOURCE 17 EUCALYPTUS UROPHYLLA X E. GRANDIS

Introduction

The striking growth superiority of the natural eucalypt hybrid 12 ABL x E. saligna and PF1 clones in comparison with pure eucalyptus species locally introduced was demonstrated for the first time during the 1960s in Pointe Noire, Congo (Chaperon, Quillet, 1977; Vigneron et al., 2 000). This has accounted for the development of suitable nursery techniques for clonally propagating true-to-type by rooted cuttings the relevant natural eucalypt hybrids selected (Martin, Quillet, 1974; Chaperon, Quillet, 1977). Since the late 1980s, artificial Eucalyptus urophylla x Eucalyptus grandis hybrid clones derived from a comprehensive genetic improvement program have been progressively replacing the former 12 ABL x E. saligna and PF1 clones used till then (Vigneron, 1992; Vigneron et al., 2000). These new hybrids, although superior in terms of yield and technological properties, did not respond however so satisfactorily to the mass clonal propagation methods developed for the 12 ABL x E. saligna and PF1 clones. With a view to improve this situation, special efforts were made in the early 1990s to intensify the cultivation and management of the field established stock plants (Basset Photo 1. Collection of shoots from coppicing stumps in the field Candeau, 1993; Laclau, Bouvet, to produce BO rooted cuttings. 1994), but the results remained far Photo O. Monteuuis. below the expectations with too low rooting rates and a substantial variation in phenotypic conformity among Getting the first rooting in suitable nursery conditions the resulting clonal offspring. More generation of nodal cuttings trimmed from 50 to consideration was therefore given to 70 cm long sprouting coppices. the possibility of using cuttings pro- of rooted cuttings: These are produced by 25-35 cm duced by container-grown stock plants the mobilization high stumps of 3 year-old field grow- instead of field established ones ing trees, established at a density of (Marien, Saya, 2003), as successfully phase 800 trees/ha (photo 1), 45 days on experimented with many different average after these latter had been arborescent species in temperate and The first and determining step felled, as described by Martin and tropical countries (Monteuuis, 1993; of the technique used for clonally Quillet (1974). Monteuuis et al., 1987 and 1995). propagating by rooted cuttings field These coppicing shoots, com- This paper reports on the development selected E. urophylla x E. grandis prising 5 to 6 long internodes, are of this technology for efficiently mass hy brids consists in getting the first brought immediately after field collec- propagating E. urophylla x E. grandis generation of vegetative copies from tion to the nursery to be trimmed into selected clones at the Unité de the field growing selected ortets. This cuttings. The reddish pigmentation of Recherche sur la Productivité des so-called “mobilization” phase, also certain of these shoots reflects their Plantations Industrielles, “UR2PI” for referred to as “B0” generation strong vigour and has been observed, short, in Pointe Noire. (M onteuuis, 1993), results from the in eucalypts as well as in different BOIS ET FORÊTS DES TROPIQUES, 2008, N° 297 (3) 18 RESOURCE MANAGEMENT EUCALYPTUS UROPHYLLA X E. GRANDIS

Photo 2. Photo 3. A BO nodal cutting trimmed Rooting of BO generation nodal cuttings in Sappi trays. from a stump coppice. Photo O. Monteuuis. Photo O. Monteuuis.

other species, to be associated with a mist water sprays maintained at restricted to 5 g of NPK 13-13-21 pro- poor rooting ability (Monteuuis, 8 seconds every minute during the vided in granular formulation per cut- 1993; Monteuuis et al., 1995). Only 6 hours following the transfer, to pre- ting, while fungicide and insecticide the semi-lignified middle portion of vent hydrous stress. Spray regime is treatments remain the same as for the this coppice is used to make by cutting reduced to 15 seconds every 10 mn rooting phase. just above a node 1 or 2 cuttings of 8 for the next 14 days, and finally to 15 The two-node cuttings trimmed to 10 cm as overall average length. seconds every hour for the 15 last from field coppices usually produce These cuttings consist of a 5 to 8 cm days of the rooting phase, from 9 till two shoots, one per axillary bud at long basal internode and two opposite 16 o’clock. During this rooting the axil of the two lateral leaves. half leaves separated by a second period, fertilization consists of Usually, one of these two shoots out- internode of varying length – it can be weekly applications of 0.06g of NPK grows the other one to form the main only 1cm long. Half of the surface of 1-1-5 in a granular formulation and stem of the new plant, notwithstand- these 2 to 4 cm-long leaves is removed 0.09 g of “Hakaphos Rouge” (NPK 8- ing that the initial competition to reduce evapotranspiration and 12-24, + 4% magnesia and oligonu- between the two shoots hinders its water stress risks, as illustrated in trients) in aqueous solution per cut- development. Moreover, such axillary photo 2 and photo 6 b. ting. Water solutions of fungicide – shoots start to elongate at a certain The so-prepared two-node cut- Banko Plus 1.5 ml/l – and insecticide angle of diversion from the main ver- tings are then soaked in an aqueous – 10 ml/l of Cypercal 50 EC tical axis of the cutting (photo 4). fungicide solution of 1.5ml/l of (50Cyperméthrine 50 g/l) – are also Manual shearing is therefore needed Banko Plus (550 g/l Chlorothalonil + sprayed every week on the cuttings. to keep only the more vigorous and 100 g/l Carbendazime) before dip- At the end of the 30 day-long upright axillary shoot from these field ping their base into a 0.8% powder rooting period, the misting regime is stump-issued rooted cuttings. concentration of Indole Butyric Acid reduced to 15 seconds every two The rooted cuttings, maintained “Chryzoplus” and insertion into 34 x hours for 4 days, prior to transfer of since the beginning in SAPPI trays, 34 cm-wide by 9 cm-deep SAPPI trays the cuttings in the SAPPI trays for 45 reach an overall size of 30-32 cm in consisting of 7 x 7 = 49 alveolar cells days to acclimatizing conditions. height at the end of the 45 day-long of 50 ml each (photo 3), filled with a These consist in exposing the cuttings acclimatization phase. They were pre- rooting substrate made of 8 volumes to full natural light by totally removing viously used as planting material for of vermiculite and 2 volumes of per- the shading clothe installed over the field clonal tests or for industrial lite. As soon as completed with the rooting facilities, and to reduce the clonal plantations. With the new sys- 49 cuttings, the trays are transferred watering to 15 mn one to twice a day tem, they are exclusively utilized for for 30 days to the rooting area, on depending on the local climatic con- producing advanced generations of benches at around 80cm above ditions to prevent water stress. During intensively managed stock plants, ground level, under 50% shade and this acclimatization phase, feeding is according to the following procedure. BOIS ET FORÊTS DES TROPIQUES, 2008, N° 297 (3) GESTION DE LA RESSOURCE 19 EUCALYPTUS UROPHYLLA X E. GRANDIS

Managing the subsequent generations of propagation by rooted cuttings

The actively growing juvenile- like shoots produced by the initial B0 generation of container-grown stock plants described above are collected as soon as they reach an overall length of 5 to 7cm, that corresponds to three nodes or pairs of opposite leaves in addition to the terminal shoot apex (photos 6). This must be considered as the standard for suit- Photo 4. The resulting rooted cuttings displaying varying degrees of stem straightness. able cuttings. These terminal shoot Photo O. Monteuuis. cuttings will be rooted and then accli- matized following the same procedure and under the same conditions These B0 rooted cuttings are same clone, planted at 12 x 12 cm as for the B0 generation of cuttings transplanted into 60 cm-long x each from another, and is placed on an detailed previously. 40 cm-wide and 16 cm-deep contain- 80cm-high elevated support under Once they reach 30 to 32 cm in ers locally made by stacking two intermittent watering – 2 to 3 daily height, the container-grown plants “stamp” plastic cases one over the sprays of 5 minutes each – and full nat- issued from the B1 and subsequent other as illustrated in photo 5. ural light. They are fertilized every week generations of serial propagation by The so-obtained containers are up to saturation with an aqueous solu- cuttings (Monteuuis et al., 1987; filled with a cultivation substrate con- tion of 5 g/l of NPK 13-13-21 plus 1 g/l M onteuuis 1993; Aimers-Halliday sisting of black fine sandy soil (8 vol- of “Hakaphos Rouge” (NPK 8-12-24, + et al., 2003) are shortened to 2 cm umes) mixed with wood charcoal (2 4% magnesium and oligonutrients). above the substrate level to be used volumes) and enriched with 5 kg/m3 of Soon after transplantation in as intensively managed stock plants, NPK 13-13-21 basic fertilizer. This mix- such conditions, these B0 rooted cut- producing the first suitable cuttings ture is scalded in boiling water during ting-issued plants are sheared back to 3 weeks later. By comparison, 5 cm 12 hours before utilization. Every reduce their main stem average height was the shortest pruning height to “stamp” container contains 15 B0 gen- from 30-32 cm to about 5 cm. This keep B0 generation stock plants eration-issued rooted cuttings of the operation is repeated a few times once alive, from which suitable cuttings or twice a week in order to stimulate could be collected only after one the production of as many new axillary month. Indeed, as observed for dif- shoots as possible, which start sprout- ferent species (Franclet, 1977; ing from the main stem usually 7 days Monteuuis, 1993), the cloning abil- after shearing. From this step onwards, ity of Eucalyptus urophylla x any elongating leader shoot must be Eucalyptus grandis genotypes by removed as early as possible to reduce rooted cuttings can be greatly pro- between-shoot differences that may moted by maintaining the stock induce further within-clone variation. plants as miniaturized, compact and After one month of such intensive close to the root system as possible. pruning practices, the B0 container- This is achieved by frequent pruning grown stock plants produce numerous and pinching operations which actively growing soft shoots with short induce, after a few weeks, the forma- internodes and juvenile-like opposite tion of a 2 to 3 cm large burl in the leaves. Such shoots are used to give upper part of the main stem, and rise to the second or B1 generation of from which most of suitable cuttings Photo 5. container-grown stock plants. originate profusely (photo 7). Setting the newly rooted BO cuttings in « Stamp » containers to be used as stock plants. Photo F.Mankessi. BOIS ET FORÊTS DES TROPIQUES, 2008, N° 297 (3) 20 RESOURCE MANAGEMENT EUCALYPTUS UROPHYLLA X E. GRANDIS

Collecting regularly every 3 or 4 days from the stock plants all the newly formed shoots that can be used as suitable cuttings replaces the frequent hedging and pinching practices initially needed for stimu- lating the production of such shoots. All the young shoots produced from B1 or more advanced generations of such intensively managed stock plants look similar at this stage, displaying the same morphological features, i.e. opposite and decussate leaf phyllotaxy, short internodes and small leaves like juvenile seedlings. They also demonstrate a similar high capacity for adventitious rooting and true-to-type cloning from rooted cuttings. This contrasts with the B0 gen- Photo 6 a. eration cuttings collected from field Morphological features of suitable cuttings produced by intensively coppicing stumps, which exhibit managed container-grown stock plants. Photo O. Monteuuis. alternate leaves separated by much longer internodes, mature traits and which root in lesser proportions with only one or two long adventitious roots per rooted cutting (photos 8). Under this new mass clonal production system, generations B0, B1 and B2 of rooted cuttings are used exclusively to produce the sufficient number of suitable stock plants needed to meet the annual require- ment in plantable rooted cuttings. The current figures are amounting to 12 000 000 cutting-derived planting stock per year produced from 30 000 suitably managed container-grown stock plants. Only materials deriving from the fourth (B3) or more advanced generations of serial propagation are used for field planting. This is a fundamental difference with the previous extensive technique (Martin, Quillet, 1974) utilizing exclusively Bo generation planting material obtained directly from stump coppicing shoots after felling of the 3 year-old ortets.

Photo 6 b. Morphological characteristics of BO nodal cuttings from stump (top) versus terminal shoot ones from intensively managed container-grown stock plants (bottom). Photo A. Saya. BOIS ET FORÊTS DES TROPIQUES, 2008, N° 297 (3) GESTION DE LA RESSOURCE 21 EUCALYPTUS UROPHYLLA X E. GRANDIS

Photo 7. Most of the suitable cuttings originate from a burl developed in the upper part of the contained-grown stock plants induced by intensive pruning practices. Photo A. Saya.

Advantages The new method developed has tremendously improved the mass of using cuttings clonal propagation by rooted cuttings produced from of outstanding field clones like 18- 147, which could not be efficiently intensively mass produced with the former managed extensive technique. The main advantages of this container-grown new container-grown and intensively stock plants managed stock plant technique are: ▪ It is more efficient than the previous field system, not adapted to the mass The inability of most of the propagation by rooted cuttings of E. urophylla x E. grandis genotypes to most of the E. urophylla x E. grandis be mass-clonally propagated using field-selected ortets; the former extensive technique, ▪ Much higher quantity of rooted cut- which was successfully developed tings can be produced per stock plant, and experienced for many years with averaging 400 per annum versus 35 Eucalyptus PF1 and E. 12 ABL x E. for field-established stumps. In other saligna hybrid, demonstrates once words, 1.12 m2 of container-grown again that eucalypts are liable to stock plants – 15 units per 0.6 m long behave quite differently according to x 0.4 m wide “stamp” container – pro- their genetic background. Significant duce annually the same quantity of differences in adventitious rooting rooted cuttings as 1 ha of stump- and more generally in organogenic derived stock plants (800 stumps/ha) capacities have been also noticed converted from industrial plantations. both in nursery and tissue culture ▪ The quality of the resulting plants is Photos 8. conditions between E. urophylla x improved: rooted cuttings with termi- Comparative characteristics of rooted cuttings produced from stumps in the field (to the left E. grandis genotypes, even as closely nal bud produced from intensively of each picture), and produced from intensively related as half-sib (Monteuuis, managed container-grown stock managed stock plants (to the right). unpublished data). plants give rise to straight, single- Photo A. Saya. BOIS ET FORÊTS DES TROPIQUES, 2008, N° 297 (3) 22 RESOURCE MANAGEMENT EUCALYPTUS UROPHYLLA X E. GRANDIS

Photos 9. R eady for planting rooted cuttings derived from intensively managed container grown stock plants. Photo A. Saya.

stemmed and true-to-type clonal off- The noticeable reduction of the tion cycles can be reduced to 7 years spring. This contrasts with field sys- within-clone variation or “C effects” versus 12 years with the previous tem derived nodal cuttings which, ( Timmis et al., 1987), by comparison extensive propagation system once rooted, needed to be first sorted with the previous field stump-derived (table I), resulting in substantial out, then hand pruned to keep only system is likely to improve greatly the space, time and money benefits. the most promising axillary shoot. quality of the field clonal tests ▪ Rooted cuttings can be produced needed for the ongoing clonal selec- sustainably all year around, whereas tion programs, which can be ana- field cuttings can be collected to be lyzed on a more reliable and sound rooted only twice a year, during the basis. Moreover, true-to-type clonal rainy seasons. offspring can be produced much ear- ▪ The stock plant area is much smaller lier in sufficient quantities for setting and located within the nursery for up once and for all at one time, only easier maintenance, monitoring and one set of rigorous clonal tests one access than the field stump stock year after the field selection of the 3- plants scattered unevenly over huge year-old ortets. In this way, the time plantation areas. needed to achieve the clonal selec- BOIS ET FORÊTS DES TROPIQUES, 2008, N° 297 (3) GESTION DE LA RESSOURCE 23 EUCALYPTUS UROPHYLLA X E. GRANDIS

Table I. UR2PI former versus new clonal selection time frame.

Former cycle using ﬁeld stump derived Years New cycle using container-grown stock plants stock plants

Field establishment of controlled pollination- 1 Field establishment of controlled pollination- derived progeny tests derived progeny tests

Field selection of candidate ortets 3 Field selection of candidate ortets for clonal for clonal tests (COC) tests (COC)

Production of clonal offspring 4 Intensive propagation from advanced from COC sprouting stumps generations of container grown stock plants and setting up of a complete (5x5) x 3 clonal test

Establishment of the ﬁrst set (3 x 3) x 3 of clonal 5 test plots

7 Clonal selection and Intensive propagation of the relevant clones selected for operational planting

Preliminary clonal selection from the year 5 8 clonal tests plots Production from ﬁeld sprouting stumps of the relevant clones selected. Establishment of the second set or conﬁrmation of (4x4) x 3 clonal test plots

Final clonal selection from the year 8 11 conﬁrmation clonal tests

Mass production of the clones ﬁnally selected 12 from ﬁeld-established stumps for operational planting BOIS ET FORÊTS DES TROPIQUES, 2008, N° 297 (3) 24 RESOURCE MANAGEMENT EUCALYPTUS UROPHYLLA X E. GRANDIS

Discussion

The advantages of using inten- ▪ E asier maintenance – weeding, the first generation of intensively man- sively managed container-grown stock feeding, pest and disease treatments aged container-grown and recently plants are becoming more and more – and control; rooted stock plants. This is consistent obvious for many eucalyptus species or ▪ More adapted to intensive manage- with other findings on different species, inter-specific hybrids (Wendling, ment – frequent pruning and pinch- especially when starting from mature Xavier et al., 2003; Titon, 2006). It can ing operations; original ortets (Monteuuis, 1993). reasonably be assumed that the tech- ▪ Higher density of stock plants per Combining serial propagation to fre- nique detailed in this paper for success- area; quent hedging practices and cutting fully mass propagating by rooted cut- ▪ G reater overall efficiency and cost collections from the same container- tings selected E. urophylla x E. grandis effectiveness. grown stock plant is definitely easier to genotypes in Pointe Noire conditions manage than a strict serial propagation can also benefit other eucalypt species Less optimal field conditions system where cuttings are collected in different environments. It is indeed may have accounted for the failure of only once or twice from the same stock much cheaper and easier to monitor the “semi-intensive” – 2500 stock plant (Monteuuis et al., 1987; Aimers- and manage than the hydroponics or plants/ha – and more particularly of Halliday, 2003). This serial-hedged sub-irrigation systems which are cur- the “intensive” – 20 000 stock combined stock plant management has rently more and more adopted for mass plants/ha, which resulted in a prema- proven to work quite satisfactorily so far producing eucalypts and other forest ture and high stock plant mortality – on the E. urophylla x E. grandis clones tree species by rooted cuttings in many field established stock plant systems in Pointe Noire, similarly to what has parts of the world (Alpoin et al., 2004; tested on the same E. urophylla x been obtained with other tropical and Jimenez, 2005). The financial aspects, E. grandis clones in Pointe Noire con- temperate species in different condi- the overall efficiency, including the ditions during the early 1990s tions, including conifers (Monteuuis, degree of sophistication and relevant (Laclau, Bouvet, 1994). 1993; Aimers-Halliday et al., 2003). skilfulness requirements, as well as the Maintaining by frequent pruning The fact that the intensive propagation final destination of the planting mate- or pinching operations, the production technique described has already been rial constitute indeed determining of shoots to be used as cuttings close successfully applied to some stock issues in choosing between nursery to the root system has been proven to plants for 5 years already without notic- and in vitro clonal propagation system, promote their ability for adventitious ing any sign of decline demonstrates and being aware that only tissue-cul- rooting and true-to-typeness develop- that the culture conditions have been tured clones comply with international ment once rooted ( Franclet, 1977; quite appropriate. However, consider- phytosanitary dispatching restrictions. Monteuuis et al., 1987; Monteuuis, ing the great number of shoots pro- All these crucial issues applied to the 1993). Such practices shorten indeed duced continuously, risks of stock plant UR2PI E. urophylla x E. grandis selected the distance between the roots and the depletion must remain a crucial con- clones mass produced for local utiliza- shoot apical meristems, whose role for cern to care about. Thus, a systematic tion warrant the new nursery technique true-to-type cloning is determining, in replacement at regular time period with developed from intensively managed other words, between the “sources new stock plants coming from the next and container-grown stock plants. “and the “sinks” from a metabolic generation of serial propagation seems The rationale for promoting mass viewpoint. The architecture of the stock highly recommendable. clonal propagation by rooted cuttings plant becomes simplified and the This report emphasizes the of selected tree genotypes by intensive within-plant variability responsible for importance of suitable nursery tech- stock plant management has been physiological gradients minimized for a niques for improving the ability for argued and demonstrated for a long more uneven physiological condition true-to-type cloning by rooted cuttings time on different arborescent species of the shoots, and assumedly a better of E. urophylla x E. grandis clones. The (Franclet, 1977). The advantages of morphologic uniformity of the resulting physiological changes induced by preferring container-grown stock plants rooted cuttings (Monteuuis, 1989). such practices, which are responsible to field-established ones for achieving The beneficial influence of the for this greater responsiveness of the this goal can be summed up as follows: serial propagation method for improv- plant material selected to be mass ▪ Better control and therefore opti- ing the ability for adventitious rooting clonally propagated are under investi- mization of stock plant environment and further true-to-type cloning of the gations at a more basic level. with regard to light, watering, soil fer- cuttings has been particularly obvious However, the practical benefits are tility, wind, etc. from one generation of cuttings to the from now on obvious, first for clonal ▪ Proximity to the misting area result- further one. The most striking difference selection, then for the large-scale uti- ing in shorter time and distance for observed in this respect was between lization of the clones selected. collecting the cuttings that can be set the B0 and B1 generations, that is to sooner with less stress under proper say between cuttings collected from 3- rooting conditions; year-old field established stumps and BOIS ET FORÊTS DES TROPIQUES, 2008, N° 297 (3) GESTION DE LA RESSOURCE 25 EUCALYPTUS UROPHYLLA X E. GRANDIS

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