Abstract
Eucalyptus urophylla S.T.Blake is an important commercial tropical plantation species worldwide. In China, a breeding program for this species has progressed through three cycles but genetic diversity and structure in the breeding populations are uncertain. A sampling of field trials from these populations was carried out to evaluate their genetic diversity and structure using 16 microsatellite loci. Significant deviations from Hardy-Weinberg equilibrium were recorded at all 16 loci in the populations. Overall expected and observed heterozygosity (He and Ho) estimates of 0.87 and 0.59 respectively for the first cycle population, and 0.88 and 0.60 respectively for the third cycle population, revealed reasonably high levels of genetic diversity. The genetic differentiation coefficient (Fst) revealed low differentiation among pairs of provenances (from the species’ native range) comprising the first cycle population (range: 0.012–0.108), and AMOVA results showed that the majority of molecular genetic variation existed among individuals rather than among provenances for the first cycle population and among individuals rather than among field trial sources in the third cycle population. Levels of genetic diversity appeared to remain unchanged from the first to third cycle populations, and the results indicate prospects for maintaining if not increasing diversity through recurrent breeding. Likely effects of artificial directional selection, prior to sampling, on both populations examined are discussed along with implications for future E. urophylla breeding.
Highlights
Eucalyptus urophylla S.T.Blake is a tall forest tree that has a natural distribution spanning seven of the Lesser Sunda Islands in eastern Indonesia, where it is mostly found growing on volcanically derived soils, and it extends into East Timor
The natural stand origins of some of the genetic materials included in the breeding populations and examined in this study are known to be on the island of Wetar, Indonesia, and could be classified as E. wetarensis according to Pryor et al [1] and Nicole [18]
On account of a number of factors, including the origin of genetic materials used to develop the founding population for the E. urophylla breeding program in China, deficits of heterozygotes were found for the 16 microsatellite loci examined in both the founding and the descendant breeding populations of E. urophylla
Summary
Eucalyptus urophylla S.T.Blake is a tall forest tree that has a natural distribution spanning seven of the Lesser Sunda Islands in eastern Indonesia, where it is mostly found growing on volcanically derived soils, and it extends into East Timor. Across this natural range, the species can vary from a tall forest tree up to 45 m high to a shrub like form of less than 2 m [1,2]. Cross-pollination in the species is mostly effected by insects and birds [3] and though self-compatible, it is predominantly outcrossing but with a mixed mating system in natural stands [4] On lower slopes it often co-occurs with Eucalyptus alba Reinw. It was first introduced to China in 1971 [7]
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