Session 3 Genetics, Provenance Trials, and Vegetative Propagation

Session Papers

Vegetative Propogation 

Vegetative Propagation of Adult Faidherbia albida by Branch and Root Cuttings

P. Danthu¹

Abstract

Propagation of cuttings from adult Faidherbia albida was done using lignified branch cuttings with diameters ranging from 7-15 mm at the bud breaking stage, and inverted root fragments. Easy clonal propagation of mature trees under field conditions is possible. Resulting growth may then serve as stock for cloning by horticultural or in vitro means.

Introduction

Although it is easy to vegetatively propagate young Faidherbia albida in the nursery using root cuttings (De Fraiture and Nikiéma 1989) or in vitro with cotyledon buds (Duhoux and Davies 1985), it is very difficult to clone adult trees. Trees generally lose their ability to vegetatively propagate as they age. F. albida resprouts from the stump and produces root suckers naturally (CTFT 1988). It is possible to propagate the species from adult trees utilizing these materials. Gassama (1989) cloned mature F. albida using root suckers with micropropagation techniques.

However, a number of factors make this propagation method tedious and expensive. Utilization of poorly lignified—and therefore fragile—stock that requires transport to and handling in the laboratory before establishment is costly and difficult under field conditions. Further, obtaining sprouts requires felling of selected individuals; all trees do not produce root suckers and it is often necessary to stimulate their production by injuring shallow roots. Protection of shoots from browsing poses another constraint, as does deterioration of cuttings during lengthy collection trips.

With these constraints in mind, trials were carried out to develop a horticultural method to clone adult trees with rapid and easy collection of material which can tolerate brief storage before being transferred to the nursery. Lignified branch cuttings harvested from the crown and segments of shallow roots were used.

Materials and Methods

Trials were carried out using adult trees 40 years old from the Bel Air Park in Dakar. Cuttings were collected in the morning and for the most part transferred the following day to the Harm nursery. No particular precaution was taken during transport and storage.

Cuttings were planted in clear polyethylene tubes (25 x 12 cm) or in wooden crates (55 x 55 x 20 cm) enclosed by shaded glass panels. The medium was a mixture of sand and crushed basalt (Badji et al., in press). The temperature, which was not controlled inside the glass panels, varied from 18-28 C. The atmosphere within the panels was saturated twice daily by a mist sprayer. Two antifungal treatments, Benlate® (70 mg L^-1) and Aliette® (1 mg L^-1), were applied once a week on a rotating basis. Each cutting, 15 cm long with 5-6 nodes, was treated with a talc-based powder containing 4% IBA (β-indole butyric acid) and pressed basally 5 cm into the medium. The first trial was to determine the optimum time for collecting cuttings from F. albida. Starting in September, cuttings of 7-15 cm diameter were collected on a monthly basis. Survival and rooting rates were estimated 2, 3, and 4 months after planting. A cutting was considered as rooted when at least one root became visible through the clear polyethylene tube. Cutting diameter was the second factor tested, and was divided into four classes (2-4 cm, 4-7 cm, 7-11 cm, and 11-15 cm). The measurements were identical to those of the first trial.

The root sections were about 10 cm long (De Fraiture and Nikiéma 1989). Three nursery treatments were tested—shallow (covered by 1 cm of medium), deep (buried in approximately 8 cm of substratum), or inverted (the distal end of the root fragment was pointed upwards). Analyses of variance and comparisons of averages (Newman-Keuls test at 5% confidence levels) were carried out following angular transformation of the frequencies.

Results

Branch Cuttings

Survival and rooting rates of F. albida cuttings was dependant on the time of collection (Table 1). Material gathered in July or in September when trees were totally defoliated failed to root. Branch cuttings collected in October at the bud breaking stage had 37% survival after 60 days and 19% rooting after 120 days. After October, cuttings showed declining tendency to survive or root as the collection time progressed towards foliating season. Leaf removal or retention at the time of planting had no influence on survival or rooting.

Small-diameter (<4 mm) cuttings taken in October had 4% survival rates at 90 days and 0% at 120 days. Larger cuttings 7-15 mm) gave the best results—approximately 20% survived and rooted after 120 days (Table 2).

Rooting of cuttings with diameters between 7-15 mm collected in October commenced after 3 months (Tables 1 and 2). The resulting root systems were fibrous, and numerous roots emerged from the base of the cutting without callus formation (Fig. 1). After rooting, cuttings developed 1-2 buds which generally sprouted a pair of axillary leaves. From these, branches emerged and proceeded to elongate (Fig. 2).

Root Cuttings

Only the inverted root cuttings gave relatively good results. Twenty-two percent of the inverted root sections formed at least one stem originating from the buried portion (i.e., the distal end) of the root sections (Figs. 3 and 4). In rare cases, root formation was observed (Fig. 3). Some individuals produced up to six stems (Fig. 4). Within the diameter range tested (10-40 mm), root diameter had no influence on frequency and time to shoot formation.

Table 1. Survival and rooting rate (%) of Faidherbia albida cuttings 60, 90, and 120 days after establishment as a function of the month of collection, Dakar, Senegal, 1990.

Table 2. Survival and rooting rate (%) of Faidherbia albida cuttings 60, 90, and 120 days after establishment as a function of cutting diameter (mm) (length = 15 cm), Dakar, Senegal, 1990.

Figure 1. Branch cutting from an adult F. albida rooting 4 months after planting (x 0.3), Darkar, Senegal, 1990.

Figure 2. Emergence of an axillary branch (x 0.5) from a rooted cutting of F. albida, Senegal, 1990.

Figure 3. Emergence of root and root sucker (x 0.5) from a root cutting of an adult F. albida, Dakar, Senegal, 1990. 

Figure 4. Multiple root sucker formation on a root cutting (x 0.5) from an adult F. albida after 4 months of culture, Dakar, Senegal, 1990.

Discussion

Rapid clonal production of adult F. albida was accomplished in the nursery using branch cuttings and root cuttings. Previously, vegetative propagation was done with root fragments of 8-month old trees (De Fraiture and Nikiema 1989). Our work demonstrates that this can be done with material from adults as well. Propagation of lignified branches from the crown of adult trees is only effective for cuttings 7-15 mm in diameter and only when collected from trees in the bud breaking stage at the beginning of the dry season.

Rooting percentage of cuttings was generally low (20%). This must be improved through modification of culture conditions, such as better control of temperature, or more efficient use of growth hormones. Improvement of cultural techniques may also serve to lengthen the optimal time for collecting cuttings.

From a practical standpoint, the two types of material used are different—shoots from root fragments are juvenile material and, therefore can be immediately used for clonal multiplication in vitro (Gassama 1989). Rooted cuttings, on the other hand, are characterized by branch plagiotrophy, poor growth, and lack of a taproot, and therefore have less capacity to rejuvenate and can only be vegetatively propagated when young.

However, since cuttings are abundant, easier to collect than root sections, and tolerate up to 5-6 days' storage in a moist cloth, this material is of greater potential for clonal increase of selected genotypes. Shoots from rooted cuttings could be used in a 'rejuvenation' program, with propagation by 'chain' micrografting or with in vitro propagation as is now done with numerous other forestry species (Franclet et al. 1987).

Acknowledgment. This research was financially supported by the International Development and Research Centre (IDRC) (the Vegetation Project, Senegal, 3P-87-0267-AFNS).

References

Badji, S., Ndiaye, I., Danthu, P., and Colonna, J.P. (In press). Vegetative propagation studies of gum ara-bic trees. Propagation of Acacia Senegal L. Willd. using lignified cuttings of small diameter with eight nodes.

CTFT (Centre technique forestier tropical). 1988. Faidlierbia albida (Del.) A. Chev. (Synonyme Acacia albida Del.) Nogent-sur-Marne, France: CTFT. 72 pp.

Duhoux, E., and Davies, D.W. 1985. Caulogenèse à partir des bourgeons cotylédonaires d'Acacia albida et influence du saccharose sur la rhizogènese. Journal of Plant Physiology 121:175-180.

De Fraiture, A., and Nikièma, A. 1989. Mise au point de techniques de bouturage sous chassis des racines d'Acacia albida Del. Technical Internal Report. Ouagadougou, Burkina Faso: Centre national de semences forestieres. 16 pp. (Limited distribution.)

Franclet, A., Boulay, M., Bekkaoui, F., Fouret, Y., Verschoore-Martouzet, B., and Walker, N. 1987. Rejuvenation. Pages 232-248 in Cell and Tissue Culture in Forestry. Volume 1. General Principles and Biotechnology. (Bonga, J.M., and Durzan, D.J., eds.). Martinus Nijhoff, Dordrecht, Netherlands.

Gassama, Y.K. 1989. Culture in vitro et amélioration symbiotique chez Acacia albida (Leguminosae) adulte. Pages 286-290 in Trees for development in Sub-Saharan Africa: proceedings of a regional seminar held by the IFS, Nairobi, Kenya, 20-25 February. Kenya: International Foundation for Science.

Footnote__________

1 Centre technique forestier tropical (CTFT)/Institut senegalais de recherches agricoles (ISRA), B.P. 2312, Dakar, Senegal.

Danthu, P. 1992. Vegatative propagation of adult Faidherbia albida by branch and root cuttings. Pages 87-90 in Faidherbia albida in the West African semi-arid tropics: proceedings of a workshop, 22-26 Apr 1991, Niamey, Niger (Vandenbeldt, R.J., ed.). Patancheru, A.P. 502 324, India: International Crops Research Institute for the Semi-Arid Tropics; and Nairobi, Kenya: International Centre for Research in Agroforestry