Genetic variation in wood specific gravity among half-sib families of chir pine (Pinus roxburghii sargent)

Chir pine (Pinus roxburghii) is an important tree species that grows all along the Himalayas. Wood specific gravity of chir pine before and after removal of extractives from wood increment cores was assessed from a 22-years-old progeny test in Himachal Pradesh, India. These values averaged 0.433 and 0.425, respectively. A large amount of genetic variation among the 58 half-sib families was found as indicated by range of values, additive coefficient of variation, variance estimates and narrow-sense heritability values for these traits. Moisture and extractive content averaged 86.259% of oven-dry weight and 2.003% of extractive-free oven-dry weight, respectively. Wood extractive content was highly variable and the family differences were highly heritable (hf2 = 0.5831). There was wide variability in moisture content, but a large portion of it was due to environmental or non-additive component of genetic variation. Heritability on family mean basis was found to be lower than that on individual tree basis for each trait. Estimated gain in specific gravity resulting from 30 to 50% family selection ranged from 0.0080 to 0.0127. Growth data and specific gravity were not significantly correlated implying that selection for higher growth rate would not necessarily result in reduction in wood specific gravity in chir pine.