Analysis of genetic diversity in Eucalyptus Grandis (Hillex Maiden) seed sources using ISSR molecular markers
Eucalyptus grandis (Hill ex Maiden) is an economically important tree species that is native to the Australian continent and its northern neighbours, where it is grown primarily for its hard wood timber and pulp for paper industries. The species was introduced in the African continent as a railroad fuel wood and pulp wood source. It is widely grown in tropical countries such as South Africa, Kenya, Angola, Ghana, and Zimbabwe. Improved varieties of E. grandis can enhance production and help meet the local demands of its wood products. Similarly, planting in agroforestry systems can provide revenue for small-scale farmers. Although knowledge of genetic variation is vital for the sustainable management of the species under cultivation, little information on genetic diversity of the seed sources is currently available. Low genetic variation may lead to unsustainable production through inbreeding depression or inability to adapt to changing environmental conditions. In order to preserve and exploit the valuable genetic resources of tropical trees such as E. grandis, a systematic assessment of the available genetic variability within the existing seed sources is necessary. Inter-Simple Sequence Repeats (ISSR) marker analysis was used to assess the genetic variation between and within existing local seed sources of the species currently being used in Kenya. Improved E. grandis seeds currently being planted by farmers as introduction from S. Africa were included in the study. In total, 180 individuals from six seed source were assessed at 41 ISSR loci. Out of the 41 bands generated, 27(65.9%) of them were polymorphic. Cluster analysis (dendrogram) generated by UPGMA showed grouping together of the Western Kenya seed sources except for the seed source from Kaimosi. Variation also occurred among the South African seed source, which clustered with the Western Kenya seed sources and closely to the Zimbabwean seed source. The results therefore indicate that both international and national based strategies for conservation of the species are crucial. Thus, ISSR-PCR technology is a reliable, rapid (high throughput), and cost effective marker system that can be used to study genetic variation and genetic relationships among E. grandis seed sources. The highest variation was attributed to variation within (73.6%) than between seed sources, suggesting that most of genetic variation within species can be captured by sampling within a single seed source.