Silvicultural And Conservation Techniques For Khaya Grandifoliola C. Dc. In Southern Nigeria

ABSTRACT

Khaya grandifoliola, an important economic hardwood species, has been severely depleted by

overexploitation. This necessitates its ex-situ conservation and requires in-depth knowledge of

nursery handlings, seed storage, in-vitro and ex-vitro propagation on which information is sparse.

Therefore, silvicultural requirements for conservation and sustainable use of K. grandifoliola in

some parts of southern Nigeria were investigated in this study.

Seeds of K. grandifoliola were purposively sourced from forested areas of Cross River (Boki and

Kutia), Ondo (Ayegunle-Akoko, Oba-Akoko and Owo) and Oyo [National Centre for Genetic

Resources and Biotechnology (NACGRAB), Ibadan] states and assessed for length, width and

weight. Freshly collected (Control) seeds (n=100) were tested for viability using standard

procedure. Seeds (n=100) from each of the sources were planted and 30 competitive seedlings

were assessed for growth characters. Seeds (n=2000) were selected and 500 each were stored for

20 weeks at Ambient Room Temperature (ART: 28.0±2.0oC), Short Term genebank (ShT:

24.0oC), Freezer (FrZ: - 6.0oC) and Long Term genebank (LgT: -17.0oC). Monthly, seeds

(n=100) were randomly selected from the four storage conditions and sowed in sterilised river

sand for viability test. Single node cuttings treated with Indole Butyric Acid (IBA), Napthalene

Acetic Acid (NAA) and Indole Acetic Acid (IAA) at (0, 25, 50, 150 and 200 mg/L) using sand,

sawdust and 1:1 sand-sawdust were assessed for macropropagation. In-vitro culture of embryo

on Murashige and Skoog (MS) medium + Benzyl Amino Purine (BAP) + NAA + Adenine

Sulphate (ADS) was studied. Deoxyribonucleic Acid (DNA) samples were collected from juvenile

leaves of K. grandifoliola from the 30 competitive seedlings and tested for molecular genetic

diversity using six Random Amplified Polymorphic DNA (RAPD) (OPD-08, OPD-11, OPD-13,

OPA-18, OPD-18, and OPD-20) primers. All experiments were laid out in completely

randomised design. Data were analysed using descriptive statistics and ANOVA at α0.05.

Seed sources significantly affected the seed weight (0.3±0.06g at Owo to 0.5±0.11g at

NACGRAB). Seed viability ranged from 88.0% at Oba-Akoko to 98.0% at NACGRAB while

seedling height was 21.7±8.27 cm at Owo and 29.9±5.30 cm at NACGRAB; the number of

leaves was 30.8±6.51 at Boki and 43.2±12.78 at NACGRAB. After 20 weeks, only ShT seeds

had 70.0% viability compared with 98.0% for control. The highest number of roots per cutting

UNIVERSITY OF IBADAN LIBRARY

iii

was observed in cuttings treated with 150mg/L IBA in sawdust. Embryo culture using MS +

0.05mg/L BAP + 0.1mg/L NAA + 10mg/L ADS gave the highest number of nodes (4) and root

length (7.5 cm) while pure MS produced 2 nodes and 1.5 cm root length. The RAPD markers

revealed genetic similarity among K. grandifoliola sources. Ninety-four scorable polymorphic

bands were generated from the six primers selected for amplification. An average of 18.2

amplicon per primer was obtained giving amplification products of 4-27 with primer OPD-08

producing the highest.

Viability of Khaya grandifoliola seeds was highest at 24.0oC within 20 weeks of storage, while

macropropagation was best with stem cuttings treated with 150 mg/L Indole Butyric Acid in

cured sawdust. The Random Amplified Polymorphic DNA markers were effective for its

molecular characterisation.

Keywords: Khaya grandifoliola, Morphological traits, Seed storage, Ex-situ

conservation, In-vitro propagation.