Estimates of genetic parameters and genetic gains for growth traits of two Eucalyptus urophylla populations in Zululand, South Africa
In South Africa, Eucalyptus urophylla is an important species due to its disease tolerance to fungal diseases such as Crysoporthe austroafricana and the Coniothyrium sp. cankers. It is mainly planted as a parental species in a hybrid combination with E. grandis. Generally, the E. grandis × E. urophylla hybrid has better disease tolerance and higher wood density than pure E. grandis. The current strategy is to maintain large breeding populations of both parental species in order to provide improved elite selections for hybrid crosses on a regular basis. With this in mind, two E. urophylla populations, consisting of five provenance/progeny trials, were established in the subtropical region of Zululand. The aims of this study were, firstly, to determine the magnitude of genotype × environment interaction of E. urophylla in Zululand; secondly, to estimate genetic parameters and correlations for diameter at breast height (DBH), height and volume; and thirdly, to identify selections to advance the current breeding population as well as to hybridise with E. grandis. Results indicated that genotype × environment interaction effects would be practically negligible for growth in Zululand and therefore a single breeding population will be appropriate. In general, all growth traits were under low to moderate genetic control, with narrow-sense heritabilities ranging between 0.14 and 0.48 for volume. The genetic correlations between growth traits were high (0.98 and 0.99 for DBH–volume). This is an indication that DBH is a sufficient growth measure to use in E. urophylla breeding programmes. Best linear unbiased prediction estimates indicated that a selection scenario of 200 individuals will generate genetic gains of 44.7% over the population mean. The estimated gains for the top 50 individuals that could potentially be used as hybrid parents to cross with E. grandis was 59.8% over the population mean.
Keywords: Eucalyptus urophylla, genetic correlations, genetic gains, genetic parameters