| Pinus patula is a closed-cone pine that has a rather narrow, but long, distribution in Mexico. Approximately one million hectares of P. patula plantations have been established in the tropics and sub tropics for saw-timber and paper products. South Africa has more than 300,000 hectares under operational management. Since 1986 the CAMCORE Co-operative has sampled 25 provenances and 624 mother trees of P. patula in Mexico. During December 1990, a series of five trials of open-pollinated P. patula family/provenance seedlots were established adjacent to each other at Maxwell in KwaZulu-Natal, South Africa. These trials are 10.5-years-old and offered a unique opportunity to sample material from the entire geographic range of the species grown on a single site.; Nine hundred and seventy-two individual trees, representing 12 provenances and 108 half-sib families were sampled non-destructively. Wood anatomical properties (wood density traits, tracheid length and tracheid cross-sectional properties) were measured using gamma ray densitometry and image analysis. The phenotypic variation in wood properties was characterised at the provenance, family and individual tree level. Provenance differences were strong and significant for most wood properties, while large individual tree-to-tree variation existed for all wood properties.; The additive genetic control of wood properties varied from zero (for tracheid length from ring 8) to moderately strong (h2 = 0.51) for tracheid radial diameter. Heritability estimates for wood density traits were slightly lower than what have been reported by other authors. Contrary to most reports in the literature, the findings in this study show that tracheid length and cell wall thickness in P. patula are under very weak or negligible additive genetic control. Moderate gains, ranging from one to 22 percent, are possible from direct selection on wood property traits. Predicted correlated responses show that, in some cases, indirect selection may lead to larger or equivalent responses to direct selection. |
