Genetic diversity analysis in a seed orchard of <Emphasis Type="Italic">Eucalyptus tereticornis</Emphasis>

India is the largest grower of Eucalyptus with an area of 3.943 million hectares under plantations and E. tereticornis is the predominant species in the plains of southern India with an average productivity of 12–25 m³ ha⁻¹ year⁻¹. With the aim to establish seedling seed orchards of the species, seed lots of fifteen provenances were imported from Australia and a trial was laid. In the present study the genetic diversity existing in the seed orchard was estimated using ISSR–PCR. Seven ISSR primers amplified 663 amplicons in the size ranging from 255 to 2,711 bp. The total number of polymorphic bands varied from 59 to 123 with 100% polymorphic banding profiles. The average gene diversity (Hj) of all the provenances ranged from 0.0589 to 0.1109 and the total gene diversity estimated was low (H _T = 0.130) when compared to the earlier reports from other eucalypts species. Analysis of Molecular Variance partitioned the ISSR variation into inter and intra population components. The inter population component accounted for 55.2% of the variation and the intra population component accounted for 46.3% (P < 0.001). A neighbour-joining analysis was done using the dissimilarity matrix to determine the aggregation of the individuals into clusters. Existence of population structure among the populations was revealed in STRUCTURE analysis but geographical region based clustering was not observed. The assessment of intra and inter genetic variation documented in the present study suggests that, along with the phenotypic traits, knowledge about genetic diversity measured at the DNA level in individuals of seed orchards provide an objective guide for selective culling of trees for maintaining optimal diversity for enhanced genetic gains.