Abstract:
Macadamia tree is a low-input crop with high returns per unit area and hence
has high potential in poverty reduction and wealth creation. However, the genetic
diversity of Macadamia germplasm in Kenya is not yet known. Multiplication rates
are low and existing information on ecological adaptation is limited. Hence, the rate
of breeding and expansion is not commensurate with existing potential and demand.
Four main studies were carried out. The first study tested the response of 39
accessions to cuttings, grafting and tissue culture propagation methods, for
multiplication and subsequent ex situ conservation of Macadamia germplasm. Shoot
regeneration from M. integrifolia was achieved at a rate of eight shoots per explant,
using single nodal explants cultured on half strength MS medium supplemented with
2.0 mg/L BAP, 1 mg/L IBA and 30 g/L sucrose and gelled will 9 g/L Biotec agar
(pH 5.7). With the development of rooting procedures, a complete protocol will be
available for multiplication and in vitro ex situ conservation of Macadamia
germplasm in Kenya.
In the second study, analysis of 39 GPS data points using ArcView GIS 3.3
mapped the accessions on to six major agro-ecological zones; UM1, UM2, UM3,
UM4, LH1 and UHO. All accessions except five were mapped on Nitosols.
Distribution of Macadamia in relation to soils was established, and coupled with the
information on agro-ecological zoning, breeders have the opportunity for selection
and breeding to expand Macadamia acreages.
In the third study, the accessions were assessed for morphological diversity
based on a set of standard qualitative and quantitative characters of leaf, fruit and
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flower. Phylogenetic analysis based on UPGMA for leaf traits using XLSTAT
(2009) grouped the accessions into three major clusters corresponding to M.
tetraphylla, M. integrilfolia, and their hybrids. The highest morphological diversity,
81.57, was between M. tetraphylla and M. integrilfolia. After principle component
analysis, PC1 was effective in grouping the accessions in to three clusters consistent
with phylogenetic analysis. This indicates that leaf traits in Macadamia can be used
fro quick classification by breeders in the field.
The fourth study analyzed the genetic diversity of 26 out of the 39 accessions
using six AFLP primer combinations. The 26 accessions were from five populations
Bob Harries, Thika, Kirinyaga, Embu, and Meru. Genetic diversity analysis using
GenAlEx version 6.2 revealed that Bob Harries was the most genetically diverse with
the highest percentage of polymorphic loci of 80% and highest mean heterozygosity,
He of 0.295 while Thika population had the least diversity of 67.3 % of polymorphic
loci and He of 0.224. The Embu population was distantly related to all the
population and it contained a private allele, making it unique and worth for breeding
and conservation. Phylogenetic analysis using TFPGA distributed the 26 accessions
in to four clusters and exhibited a highly hybridized germplasm. The AFLP markers
were found to be very effective in genetic characterization of Macadamia and
provided sufficient information that can immediately be used by breeders for
effective sampling for selection, hybrid variety development and conservation. This
study reveals existence of high genetic diversity in Macadamia germplasm in Kenya
that is widely adapted. The germplasm should be vegetatively propagated by grafting
for ex situ conservation before finalization of a tissue culture protocol, for breeding
purposes.