Genetic variation in growth, cold tolerance and coppicing in Eucalyptus dunnii in trials in Hunan, China

Abstract

Summary Eighty-four open-pollinated families of Eucalyptus dunnii representing 14 natural stand seed sources and one seed orchard source from Australia were established at two sites in central and southern Hunan province in 2004. These were assessed at ages 2.5–3.5 y (around half the average rotation length of eucalypt plantations in China) for tree growth and stem straightness at both sites and cold tolerance at age 3.5 y at the central site. At the southern site, all trees were cut back to stumps at about age 3.5 y, following ice storms that led to stem breakage of almost all trees. Subsequently, the coppicing traits of number of sprouts per stump and DBH and height of the largest sprout per stump were assessed at 12 months after felling. Significant differences were observed among seed sources for almost all traits. At each site, average individual tree volume of the best seed source was more than 60% above that of the poorest. The magnitude of variation among families within seed sources was generally greater and more often significant than the variation among seed sources—especially for average tree volume. The magnitude of the variations observed in stem form, though significant statistically, were small. Significant seed source differences were found also for cold tolerance at the central site and for all three coppice traits at the southern site. Estimates of within—seed-source individual-tree heritability for individual-tree volume in 2007 at the southern site and in 2006 at the central Hunan site were 0.11 ± 0.07 and 0.17 ± 0.15 respectively and that for stem straightness at the southern site was 0.17 ± 0.07. Heritabilities for coppice traits, assessed only at the southern site, ranged from 0.14 ± 0.11 for number of sprouts per stump and up to 0.42 ±0.17 for DBH of the largest coppice on each stump. Heritability for cold tolerance at the central Hunan site was 0.11 ± 0.10. These heritabilities and favourable phenotypic and genetic correlations indicate selection would be effective to improve both volume and growth of subsequent coppice development. These results indicate emphasis should be placed on selecting the best candidate trees of E. dunnii regardless of their seed source for inclusion in future breeding and propagation populations of this species in Hunan. Together, the results presented support the value of investing in E. dunnii's genetic improvement; significant gains could be delivered to commercial growers and investors including enhanced financial prospects and decreased risks for commercial plantations of this species.