Trunk distortion weakens the tree productivity revealed by half-sib progeny determination of Pinus yunnanensis

Abstract Twisted trunks are not uncommon in trees, but their effects on tree growth are still unclear. Among coniferous tree species, the phenomenon of trunk distortion of P. yunnanensis is more prominent. In order to expand the germplasm genetic resources, select families with excellent phenotypic traits and provide materials for advanced generation breeding, the progeny test forest containing 93 excellent families was used as the research material. Phenotypic measurements were performed at 9, 15 and 18 years of age, respectively, and genetic parameters were estimated. The results showed as follows: (1) There were significant differences in phenotypic traits (plant height, diameter breast height, long crown diameter, short crown diameter, height under branches, degree of stem-straightness, and volume) among and within families, indicating that there was abundant variation among families and potential for selection. (2) At half rotation period (18 years old), there was a significant correlation between the traits. The proportion of trees with twisted trunks (level 1–3 straightness) was 48%, and the degree of stem-straightness significantly affected vegetative growth traits, among which plant height and diameter breast height were the most affected, and the volume loss rate caused by twisted trunk was 18.06%-56.75%, implying that trunk distortion could not be completely eliminated after an artificial selection. (3) The influence of tree shape, crown width and trunk on volume increased in turn, and the correlation between plant height, diameter breast height and volume was extremely significant. The range of phenotypic coefficient of variation, genetic variation coefficient and heritability of growth traits (plant height, diameter breast height and volume) were 44.29%-127.13%, 22.88%-60.87% and 0.79–0.83, respectively. (4) A total of 21 superior families were selected by the method of membership function combined with independent selection. Compared with the mid-term selection (18 years old), the accuracy of early selection (9 years old) reached 77.5%, indicating its feasibility. The average genetic gain and realistic gain range of the selected families were 5.79%-19.82% and 7.12%-24.27%, respectively. This study can provide some reference for the breeding of coniferous species.