Meristem Micrografting of Adult Faidherbia albida ...
Meristem Micrografting of Adult Faidherbia albida
C. Detrezl, S. Ndiayel, F. Kerbellec’
N. Dupuyl, P. Danthuz, and B. Dreyfus’
Abstract
isolatedfiom vegetative buds (apical or axillary) on branches of adult Faidherbia albida,
were grafted in vitro on 2-day old seedling. Gr&s began elongating after only 10 days in culture.
Shoots obtained by this methoa’ were used for second- and third-generation microgrfling
cycles.
MicrogrMed seedlings developed well after acclimatization in the greenhouse. This technique
resulted in capid multiplication of selected ortets on root stock derivedfiom seed. This method may
faciiitate rapid clonal increase of selected adult individuals.
Introduction
Materials and Methods
Faidherbia ulbida is characterized by great genetic
Treatment and Germination of Axenic Seedlings
variability. Clonal propagation would be a useful rool
to exploit and analyze this variability. Production of
Seeds of four F. albida provenances (Kagnobon, Mér-
selected clones could result in genetic improvement in
ina Dakhar, Bod.6, and Ovadiour) collected in Senegal
a relatively short period and would facilitate the study
by the Direction de recherche des productions for-
of symbiotic fungal and bacrerial relationships.
esti&res (DRPF) of ISRA were scarifïed by immer-
It is known that the cloning potential of trees di-
sion in concentrated H$O, for 1 h. They were then
minishes as the material ages (Bonga 1987; Franclet
copiously rinsed in sterile water, immersed in 0.1%
ei al. 1987). F. albida shoots obtained in vitro from
mercuric chloride for 30 seconds, and rinsed again in
cotyledon buds are easy to propagate, and the individ-
sterile water. Seeds were then soaked in sterile water
uals readily take root (Duhoux and Davies 1985).
for 3 to 4 h. The seeds were germinated on agar-agar
However, microcuttings obtained from root suckers of
water (0.8%) in the dark.
adult trees do not root easily (Gassama 1989).
The state of tissue maturity at the time of removal
from the adult tree cari be partially and progressively
Choice of Ortets and Preparation lof Grafts
reversed by various cultural practices, termed ‘reju-
venation’ (Nozeran 1978). The return to juvenile
Grafting stock was taken from three types of ortets:
traits, which facilitates clonal propagation, cari be
(1) axenic seedlings ar the cotyledon stage; (2) l- to
achieved by successive grafting cycles (Franclet
2-month old seedlings from Ihe greenhouse; and (3)
1977; Franclet et al. 1987). It is based on this principle
an adult tree (50 years, Bel-Air, Dakar). Ramets
that the original ‘chain micrografting’ technique pre-
(leafy, soft-[issue branches, 5-7 cm long) from ortet
sented in this paper was developed.
types (2) and (3) were collected and sterilized in 0.1%
‘).
.;,
,:
.:
1. Institut français de recherche scientitique PIIF le développement en coopération (ORSTOM). B.P. 1386. Dakar, Senegal.
Institut sénégalais de recherches agricoles (ISRA), B.P. 2312. Dakar. Senegal.
Detrez, C, Ndiaye, S, Kerbellec, F., Dupuy, N.. Danthu, P., and Dreyfus, B. 1992. Meristem micrografting of adult Faidherbiu olhida. Pages
91-95 in Faidherbia albida in the West African semi-arid tropics: proceedings of a workshop, 22-26 Apr 1991. Niamey, Niger (Vandenlxldt,
RJ., ed.). Patancheru. A.P. 502 324, India: International Crops Research Institute for the Semi-Arid Tropics: and Nairobi, Kenya: International
Centre for Research in Agmforestry.
mcrcuric chloride for 20 seconds. From these ramets.
(Bel Air soil:vermiculite; 3:1, v:v) in a grecnhouse
mcrislems. composed of meristematic domes and
under humid conditions.
their bases trimmed to a bevelled edge, and protected
by I-4 Young chlorophyllous leaves, were selected for
grafting.
Results
Reactivation and Elongation of the Graft
Ro~t Stock and Micrografting Techniques
For the three types Of ortets studied, callus formation
Two micrografting techniques were compared using
of the grafts occurred 7-10 days after insertion into
2-day old axenic seedlings as root stock: (1) top- or
the hypocotyl. The lateral clcft grafting technique
cleft-micrografting which consists of inserting the
(Figs. 1 and 2) and top-grafting technique (Fig. 3)
graft into an incision made in the terminal part of the
were successful with both the juvenile and adult or-
hypocotyl after removal of the epicotyl and the cotyl-
tets. In the case of lateral grafting, it was necessary to
edons, and (2) lateral micropraftinp onto the hypo-
CO@ whose cotyledons and meristem were left jn
place during the first 12 days following the implanta-
tion of the graft, after which they were decapitpted to
suppress apical dominante of the root stock.
Successive Micrografting Cycles-Adult Ortet
Shoots obtained after the first micrografting operation
and the cauline elongation phase of the micrografted
meristems provided a second generation of meristems
for another cycle which used the top micrografting
technique. This second micrografting was followed
by a third, done under the same conditions.
The Culture Environment
After micrografting, the plants were grown in culture
tubes (25 x 150 mm) containing 10 mL of nutritive
medium. The culture medium was composed of the
minera1 base and vitamin mix of Murashige and
Skoog (MS) (1962). with saccharose added (20 g
L-l). The pH was adjusted to 5.8, and the agar (Bacto
Difco 0.8%) was incorponted. Media were sterilized
by autoclaving for 20 min at IIO’C.
Following each micrografting cycle and after a
.:_
:.
pe.riod of elongation, the grafts were separated from
:
::.:
::::
1.
the mot stock and their rooting ability was tested on
the MS medium, with additions of either 60 g L-l of
sucrose (Duhoux and Davies 1985) or 20 g L-l of
Figure L Insertion of a
albiah micro-
sucrose and indole butyric acid (5 mg L-l) (Gassama
grafl by the lateral-cleft technique. The graft (G),
1989).
cons& of a meristem removed from an axillary
Cultures were placed in a controlled-climate
bud of a branch of an adult tree, trimmed ba-
chamber maintained at 28 k2YI and were continu-
sically to a bevelled edge, and inserted into an inci-
ously exposed to 3200 lux of artificial light. The
sion (I) made in the hypocotyl (H) of a 2-day-old
grafted seedlings were acclimatized on a substratum
seedling. (Bar = 1 mm.)
.
.
Figure 2. Elongation of a meristem removed from
Figure 3. Elongation of a meristem taken from an
an adult tree and micrografted onto the hypocotyl
adult tree, then micrografted using the top-graft-
using the lateral-cleft technique (3 weeks of
ing technique after removal of the cotyledons and
growth). The meristem and the cotyledons of the
the epicotyl of the root stock (6 weeks of growth).
root stock, kept in place for the first 15 days follow-
(Bar = 1 cm.)
ing the graft, were selected (see arrow) after the
callus formation (C). (Bar = 1 cm.)
remove the terminal bud of the root stock when callus
son (Nov/Dec, Dakar region)-19 of 24 grafts ob-
formation began. This additional manipulation did
served showed cauline elongation. The placement of
not appreciably improve the degree of rooting of the
graft. Therefore, the lateral grafting was discontinued
Table l. Frequency of elongation of grafts taken
and only top-grafting used.
from an adult ortet of Fuidherbiu albida as a func-
,I
::
On the juvenile ortets, callus formation was imme-
tion of sampling period, Dakar, Senegal, 1990.
,:
:::::
:
..:
.,....
.:
diately followed by a foliar growth and the onset of
Pheno-
Pheno-
cauline elongation after 10-12 days of growth. For the
Sampl-
logical
logical
Success
2-day old ortets, graft elongation occurred for 23 of
ing
stage of
state of
fre-
the 24 grafted plants. For the l- to 2-month old ortets,
period
ortet
ramets
quency
elongation occurred on 22 of the 24 grafts.
In the case of the adult ortet, successful grafting
NovPec
Vegetative
Foliating
l9L24
appeared to bc correlated with the date of ramet col-
Jan/Feb
Foliating
Foliated
2136
lection (Table 1). The best results were obtained with
Mar/Apr
End foliation
Fqliated
1148
ramets collected at the beginning of the foliating sea-
efficient of multiplication (i.e., the average number of
nodes produced by the foliated shoots at the end of
each of the three successive micrografting cycles) in-
creased appreciably during the second and third mi-
crografting cycles, maximizing at a value of 10.
Table 2. Frequency of elongation and coefficient of
multiplication of grafts taken from adult Faidher-
bis albida, following three successive micrograft-
ing cycles (Gl, G2, G3), Dakar, Sengal, 1990.
Micrografting Cycle
Parameter
GI’
G2
G3
Frequency of graft
19/24
6J8
10/10
elongation
Coefficient of
5 M . 2 4 X%0.32 10.2M.27
multiplication*
1. Micrografting cycle started wiL meristem harvests done
in November and December.
2. ‘I’he average number of nodes produced by two foliated
shoots after 6 weeks of culture {&SE).
Discussion
It is possible to graft in vitro meristems of F. albida
on root stock obtained from seed. Both juvenile (3
month) and adult ortets cari be used. Successful graft-
ing with adult ortets allows imrnediate procurement of
Figure 4. Growth and development of a micro-
selected individuals grafted onto seedlings, which cari
grafted individual alter transplanting in the green-
be readily used in field trials. This micrografting tech-
house (15 weeks after the micrografting
nique is advantageous as any type of bud from the
operations). (Bar = 1 cm.)
ramet cari be used, and two grafting locations on the
hypocotyl (top or lateral clef0 are suitable. The opti-
mal collection period determined by this study is in
the grafts, whether axillary or terminal on the
accordance with observations made by Danthu (1992)
branches of the ortet, made no difference in the rate of
for horticultural cutting establishment of F. albida.
elongation. Starting in January, the ramets became
Chain micrografting by the multiplication of axill-
highly infected with a fungus. despite treatment of the
ary buds produces an abundance of newly formed
ramets with a fungicide (BenlateB, 70 mg L-l) 2 days
shoots and shows a high coefficient of multiplication
before collection. Treatment with HgCI, failed to
by 6 weeks. Extrapolating this result, 6 months of
completely control this problem.
chain micrografting from one graft could result in
Micrografted individuals were maintained in a
10 000 identical grafted individuals.
greenhouse (Fig. 4). For the first 3 months of this
Although shoots have been propagated on root
._
.: . . . .
: : : . . :: .::.
-+
acclimatization period, the plants had weak stems.
stock, a suitable technique for root formation has yet
_...’
.:::<
Tbis was supplanted by a second, more vigorous stem
to be developed. We hope to achieve rooting through
originating from a basa1 axiiiary bud.
tissue rejuvenation during chain grafting. Investiga-
tions currently under way in the laboratory are aimed
at obtaining rooted clones, a necessary condition for a
.
Chain Micrografting of Adult albiak
stand improvement project of F. albida.
Tbe frequency of graft elongation increased during
Acknowledgment. The authors thank M.Y. Dom-
chain micrografting (Table 2). Likewise, the graft co-
mergues for his critical reading of the manuscript.
2
.
i
:
References
Franclet, A., Boulay, M., Bekkaoui, F., Fouret, Y.,
Verschoore-Martouzet, B., and Walker, N. 1987.
Rejuvenation. Pages 232-248 in Cell and Tissue Cul-
Bonga, J.M. 1987. Clonal propagation of mature
ture in Forestry, Volume I. General Principles and
trees: problems and possible solutions. Pages 249-271
Biotechnology (Bonga, J.M., and Durzan, D.J., eds.)
in Ce11 and Tissue Culture in Forestry, Vol.1 (J.M.
Martinus Nijhoff, Dordrecht, Netherlands.
Bonga and Don J. Durzan, eds.). Martinus Nijhoff,
Dordrecht, Netherlands.
Gassama, Y.K. 1989. Culture in vitro et amélioration
symbiotique chez Acacia alhida (Leguminosae)
Danthu, P. 1992. Vegetative propagation of adult
adulte. Pages 286-290 in Trees for development in
Fuidherhia alhidu by branch and root cuttings. These
subsahara Africa: proceedings of a regional seminar
proceedings.
held by the IFS, Nairobi, Kenya, 20-25 February.
Kenya: International Foundation for Science.
Duhoux, E., and Davies, D.W. 1985. Caulogenèse à
partir des bourgeons cotylédonaires d’Acacia
alhida
Murashige, T., and Skoog, F. 1962. A revised me-
et influence du saccharose sur la rhizogenèse. Journal
dium for rapid growth and bioassays with tobacco
of Plant Physiology 121:175-180.
tissue culture. Plam Physiology 15:473-497.
Nozeran, R. 1978. Réflexions sur les enchaînenments
Franclet, A. 1977. Manipulation des pieds-mères et
de fonctionnement au cours du cycle des végktaux
amélioration de la qualité des boutures. Etudes et Re-
supérieurs. Bulletin de la Societé Botanique Fran-
cherches 8. 20 pp. France: Afocel.
çaise 125:263-280.
C. Detrezl, S. Ndiayel, F. Kerbellec’
N. Dupuyl, P. Danthuz, and B. Dreyfus’
Abstract
isolatedfiom vegetative buds (apical or axillary) on branches of adult Faidherbia albida,
were grafted in vitro on 2-day old seedling. Gr&s began elongating after only 10 days in culture.
Shoots obtained by this methoa’ were used for second- and third-generation microgrfling
cycles.
MicrogrMed seedlings developed well after acclimatization in the greenhouse. This technique
resulted in capid multiplication of selected ortets on root stock derivedfiom seed. This method may
faciiitate rapid clonal increase of selected adult individuals.
Introduction
Materials and Methods
Faidherbia ulbida is characterized by great genetic
Treatment and Germination of Axenic Seedlings
variability. Clonal propagation would be a useful rool
to exploit and analyze this variability. Production of
Seeds of four F. albida provenances (Kagnobon, Mér-
selected clones could result in genetic improvement in
ina Dakhar, Bod.6, and Ovadiour) collected in Senegal
a relatively short period and would facilitate the study
by the Direction de recherche des productions for-
of symbiotic fungal and bacrerial relationships.
esti&res (DRPF) of ISRA were scarifïed by immer-
It is known that the cloning potential of trees di-
sion in concentrated H$O, for 1 h. They were then
minishes as the material ages (Bonga 1987; Franclet
copiously rinsed in sterile water, immersed in 0.1%
ei al. 1987). F. albida shoots obtained in vitro from
mercuric chloride for 30 seconds, and rinsed again in
cotyledon buds are easy to propagate, and the individ-
sterile water. Seeds were then soaked in sterile water
uals readily take root (Duhoux and Davies 1985).
for 3 to 4 h. The seeds were germinated on agar-agar
However, microcuttings obtained from root suckers of
water (0.8%) in the dark.
adult trees do not root easily (Gassama 1989).
The state of tissue maturity at the time of removal
from the adult tree cari be partially and progressively
Choice of Ortets and Preparation lof Grafts
reversed by various cultural practices, termed ‘reju-
venation’ (Nozeran 1978). The return to juvenile
Grafting stock was taken from three types of ortets:
traits, which facilitates clonal propagation, cari be
(1) axenic seedlings ar the cotyledon stage; (2) l- to
achieved by successive grafting cycles (Franclet
2-month old seedlings from Ihe greenhouse; and (3)
1977; Franclet et al. 1987). It is based on this principle
an adult tree (50 years, Bel-Air, Dakar). Ramets
that the original ‘chain micrografting’ technique pre-
(leafy, soft-[issue branches, 5-7 cm long) from ortet
sented in this paper was developed.
types (2) and (3) were collected and sterilized in 0.1%
‘).
.;,
,:
.:
1. Institut français de recherche scientitique PIIF le développement en coopération (ORSTOM). B.P. 1386. Dakar, Senegal.
Institut sénégalais de recherches agricoles (ISRA), B.P. 2312. Dakar. Senegal.
Detrez, C, Ndiaye, S, Kerbellec, F., Dupuy, N.. Danthu, P., and Dreyfus, B. 1992. Meristem micrografting of adult Faidherbiu olhida. Pages
91-95 in Faidherbia albida in the West African semi-arid tropics: proceedings of a workshop, 22-26 Apr 1991. Niamey, Niger (Vandenlxldt,
RJ., ed.). Patancheru. A.P. 502 324, India: International Crops Research Institute for the Semi-Arid Tropics: and Nairobi, Kenya: International
Centre for Research in Agmforestry.
mcrcuric chloride for 20 seconds. From these ramets.
(Bel Air soil:vermiculite; 3:1, v:v) in a grecnhouse
mcrislems. composed of meristematic domes and
under humid conditions.
their bases trimmed to a bevelled edge, and protected
by I-4 Young chlorophyllous leaves, were selected for
grafting.
Results
Reactivation and Elongation of the Graft
Ro~t Stock and Micrografting Techniques
For the three types Of ortets studied, callus formation
Two micrografting techniques were compared using
of the grafts occurred 7-10 days after insertion into
2-day old axenic seedlings as root stock: (1) top- or
the hypocotyl. The lateral clcft grafting technique
cleft-micrografting which consists of inserting the
(Figs. 1 and 2) and top-grafting technique (Fig. 3)
graft into an incision made in the terminal part of the
were successful with both the juvenile and adult or-
hypocotyl after removal of the epicotyl and the cotyl-
tets. In the case of lateral grafting, it was necessary to
edons, and (2) lateral micropraftinp onto the hypo-
CO@ whose cotyledons and meristem were left jn
place during the first 12 days following the implanta-
tion of the graft, after which they were decapitpted to
suppress apical dominante of the root stock.
Successive Micrografting Cycles-Adult Ortet
Shoots obtained after the first micrografting operation
and the cauline elongation phase of the micrografted
meristems provided a second generation of meristems
for another cycle which used the top micrografting
technique. This second micrografting was followed
by a third, done under the same conditions.
The Culture Environment
After micrografting, the plants were grown in culture
tubes (25 x 150 mm) containing 10 mL of nutritive
medium. The culture medium was composed of the
minera1 base and vitamin mix of Murashige and
Skoog (MS) (1962). with saccharose added (20 g
L-l). The pH was adjusted to 5.8, and the agar (Bacto
Difco 0.8%) was incorponted. Media were sterilized
by autoclaving for 20 min at IIO’C.
Following each micrografting cycle and after a
.:_
:.
pe.riod of elongation, the grafts were separated from
:
::.:
::::
1.
the mot stock and their rooting ability was tested on
the MS medium, with additions of either 60 g L-l of
sucrose (Duhoux and Davies 1985) or 20 g L-l of
Figure L Insertion of a
albiah micro-
sucrose and indole butyric acid (5 mg L-l) (Gassama
grafl by the lateral-cleft technique. The graft (G),
1989).
cons& of a meristem removed from an axillary
Cultures were placed in a controlled-climate
bud of a branch of an adult tree, trimmed ba-
chamber maintained at 28 k2YI and were continu-
sically to a bevelled edge, and inserted into an inci-
ously exposed to 3200 lux of artificial light. The
sion (I) made in the hypocotyl (H) of a 2-day-old
grafted seedlings were acclimatized on a substratum
seedling. (Bar = 1 mm.)
.
.
Figure 2. Elongation of a meristem removed from
Figure 3. Elongation of a meristem taken from an
an adult tree and micrografted onto the hypocotyl
adult tree, then micrografted using the top-graft-
using the lateral-cleft technique (3 weeks of
ing technique after removal of the cotyledons and
growth). The meristem and the cotyledons of the
the epicotyl of the root stock (6 weeks of growth).
root stock, kept in place for the first 15 days follow-
(Bar = 1 cm.)
ing the graft, were selected (see arrow) after the
callus formation (C). (Bar = 1 cm.)
remove the terminal bud of the root stock when callus
son (Nov/Dec, Dakar region)-19 of 24 grafts ob-
formation began. This additional manipulation did
served showed cauline elongation. The placement of
not appreciably improve the degree of rooting of the
graft. Therefore, the lateral grafting was discontinued
Table l. Frequency of elongation of grafts taken
and only top-grafting used.
from an adult ortet of Fuidherbiu albida as a func-
,I
::
On the juvenile ortets, callus formation was imme-
tion of sampling period, Dakar, Senegal, 1990.
,:
:::::
:
..:
.,....
.:
diately followed by a foliar growth and the onset of
Pheno-
Pheno-
cauline elongation after 10-12 days of growth. For the
Sampl-
logical
logical
Success
2-day old ortets, graft elongation occurred for 23 of
ing
stage of
state of
fre-
the 24 grafted plants. For the l- to 2-month old ortets,
period
ortet
ramets
quency
elongation occurred on 22 of the 24 grafts.
In the case of the adult ortet, successful grafting
NovPec
Vegetative
Foliating
l9L24
appeared to bc correlated with the date of ramet col-
Jan/Feb
Foliating
Foliated
2136
lection (Table 1). The best results were obtained with
Mar/Apr
End foliation
Fqliated
1148
ramets collected at the beginning of the foliating sea-
efficient of multiplication (i.e., the average number of
nodes produced by the foliated shoots at the end of
each of the three successive micrografting cycles) in-
creased appreciably during the second and third mi-
crografting cycles, maximizing at a value of 10.
Table 2. Frequency of elongation and coefficient of
multiplication of grafts taken from adult Faidher-
bis albida, following three successive micrograft-
ing cycles (Gl, G2, G3), Dakar, Sengal, 1990.
Micrografting Cycle
Parameter
GI’
G2
G3
Frequency of graft
19/24
6J8
10/10
elongation
Coefficient of
5 M . 2 4 X%0.32 10.2M.27
multiplication*
1. Micrografting cycle started wiL meristem harvests done
in November and December.
2. ‘I’he average number of nodes produced by two foliated
shoots after 6 weeks of culture {&SE).
Discussion
It is possible to graft in vitro meristems of F. albida
on root stock obtained from seed. Both juvenile (3
month) and adult ortets cari be used. Successful graft-
ing with adult ortets allows imrnediate procurement of
Figure 4. Growth and development of a micro-
selected individuals grafted onto seedlings, which cari
grafted individual alter transplanting in the green-
be readily used in field trials. This micrografting tech-
house (15 weeks after the micrografting
nique is advantageous as any type of bud from the
operations). (Bar = 1 cm.)
ramet cari be used, and two grafting locations on the
hypocotyl (top or lateral clef0 are suitable. The opti-
mal collection period determined by this study is in
the grafts, whether axillary or terminal on the
accordance with observations made by Danthu (1992)
branches of the ortet, made no difference in the rate of
for horticultural cutting establishment of F. albida.
elongation. Starting in January, the ramets became
Chain micrografting by the multiplication of axill-
highly infected with a fungus. despite treatment of the
ary buds produces an abundance of newly formed
ramets with a fungicide (BenlateB, 70 mg L-l) 2 days
shoots and shows a high coefficient of multiplication
before collection. Treatment with HgCI, failed to
by 6 weeks. Extrapolating this result, 6 months of
completely control this problem.
chain micrografting from one graft could result in
Micrografted individuals were maintained in a
10 000 identical grafted individuals.
greenhouse (Fig. 4). For the first 3 months of this
Although shoots have been propagated on root
._
.: . . . .
: : : . . :: .::.
-+
acclimatization period, the plants had weak stems.
stock, a suitable technique for root formation has yet
_...’
.:::<
Tbis was supplanted by a second, more vigorous stem
to be developed. We hope to achieve rooting through
originating from a basa1 axiiiary bud.
tissue rejuvenation during chain grafting. Investiga-
tions currently under way in the laboratory are aimed
at obtaining rooted clones, a necessary condition for a
.
Chain Micrografting of Adult albiak
stand improvement project of F. albida.
Tbe frequency of graft elongation increased during
Acknowledgment. The authors thank M.Y. Dom-
chain micrografting (Table 2). Likewise, the graft co-
mergues for his critical reading of the manuscript.
2
.
i
:
References
Franclet, A., Boulay, M., Bekkaoui, F., Fouret, Y.,
Verschoore-Martouzet, B., and Walker, N. 1987.
Rejuvenation. Pages 232-248 in Cell and Tissue Cul-
Bonga, J.M. 1987. Clonal propagation of mature
ture in Forestry, Volume I. General Principles and
trees: problems and possible solutions. Pages 249-271
Biotechnology (Bonga, J.M., and Durzan, D.J., eds.)
in Ce11 and Tissue Culture in Forestry, Vol.1 (J.M.
Martinus Nijhoff, Dordrecht, Netherlands.
Bonga and Don J. Durzan, eds.). Martinus Nijhoff,
Dordrecht, Netherlands.
Gassama, Y.K. 1989. Culture in vitro et amélioration
symbiotique chez Acacia alhida (Leguminosae)
Danthu, P. 1992. Vegetative propagation of adult
adulte. Pages 286-290 in Trees for development in
Fuidherhia alhidu by branch and root cuttings. These
subsahara Africa: proceedings of a regional seminar
proceedings.
held by the IFS, Nairobi, Kenya, 20-25 February.
Kenya: International Foundation for Science.
Duhoux, E., and Davies, D.W. 1985. Caulogenèse à
partir des bourgeons cotylédonaires d’Acacia
alhida
Murashige, T., and Skoog, F. 1962. A revised me-
et influence du saccharose sur la rhizogenèse. Journal
dium for rapid growth and bioassays with tobacco
of Plant Physiology 121:175-180.
tissue culture. Plam Physiology 15:473-497.
Nozeran, R. 1978. Réflexions sur les enchaînenments
Franclet, A. 1977. Manipulation des pieds-mères et
de fonctionnement au cours du cycle des végktaux
amélioration de la qualité des boutures. Etudes et Re-
supérieurs. Bulletin de la Societé Botanique Fran-
cherches 8. 20 pp. France: Afocel.
çaise 125:263-280.