Abstract:
Macadamia is the most important nut crop in Kenya with an estimated annual
production of about 13,510 metric tones with an estimated value of $ 4.8M. The
cultivated macadamia is derived from two species; the rough-shelled M. tetraphylla
and the smooth shelled M. integrifolia. The Kenyan macadamia industry relies on
selection of superior trees from germplasm derived from open-pollinated seeds of the
two species planted between 1946 and 1968. Twenty six macadamia accessions
sampled from five populations; Bob Harries, Thika, Kirinyaga, Embu and Meru in
central and eastern Kenya were analyzed using 110 polymorphic markers of six AFLP
primer combinations. The highest percentage of polymorphic loci of 80.0% was
observed in the Bob Harries population and the least, 67.3%, from Thika population.
Expected heterozygosity was also highest in the Bob Harries population. Phylogenetic
analysis based on UPGMA of genetic distances of the five populations revealed the
Bob Harries population, the source of macadamia germplasm in Kenya to be closely
related only to the Kirinyaga population and distantly related to the Thika population,
a preservation block of selected superior germplasm. Cluster analysis based on the 26
accessions did not distinctly separate the species indicating a high level of
heterozygosity and genetic mixture of the original gene pool used in Kenya. Analysis of
molecular variance further indicated higher genetic variation within the populations,
96%, than among the populations, 4%, and high genetic differentiation among the
accessions (theta=0.1909). The results of this study indicate high genetic diversity
within the Kenyan macadamia germplasm. This information can immediately be used
for enhanced breeding and more effective sampling of populations for conservation.
