Abstract: [Objective] Wood density is an important economic trait that is targeted in the second round of genetic improvement of slash pine(Pinus elliottii) in Guangdong. To provide theoretical and method for breeding fast-growing and high-quality germplasm of slash pine, the effectiveness of wood density assessment with the resistograph instrument was compared with the traditional volumetric method in current study, and the genetic variations in wood properties and growth were analyzed.[Method] Thirty-two open-pollinated families of slash pine in Taishan city, Guangdong province were tested. For the same individual, the resistograph readings (amplitude) and diameter inside bark were rapidly assessed of live trees in a progeny trial, and the whole core was extracted for wood basic density measurement with volumetric method. The correlations between traits and the trait heritabilities and the selection efficiency were estimated using Asreml statistic software.[Result] 1) Positive phenotypic correlation coefficient (0.659) between amplitude and wood density was determined at individual-tree level. A linear regression equation for prediction of wood density based on amplitude was established (model R²=0.393). 2) The genetic correlation between amplitude and wood density was also stronger (0.738). At the family level, wood density and amplitude were under medium genetic control. The family heritability was higher for amplitude (0.618) than for wood density (0.410). The efficiency of using amplitude as a means of indirect selection for improvement of wood density was 91% at the family level. These result indicate that it is efficient to use the resistograph for the indirect selection of high wood density. 3) To reduce the increasing trend caused by the friction of the shaft with the wood, adjustment of the resistograph profiles was made. However, the phenotypic and genetic correlation in wood density, as well as the heritability did not increase. 4) The family heritability for diameter inside bark was 0.596. Wood density and amplitude had no significant genetic correlation with diameter, whereas the phenotypic correlations were significant, which were 0.272 and 0.493. It implies that the wood density would not be reduced while improving the growth trait in slash pine.[Conclusion] The resistograph had advantages in rapid, nondestructive and relatively accurate measurement, and could be used to assess relative wood density and diameter inside bark of live trees in slash pine. It may play important role in genetic improvement in wood properties and growth trait. The efficiencies of direct and indirect selection for wood density, as well as selection for growth, were higher at family level than at individual level. To select individual performing well in wood properties and growth in slash pine, it is more reliable to combine family selection and within family selection.

Key words: Pinus elliottii, wood density, resistograph instrument, genetic correlation, indirect selection