Age-Five Results from the Cooperative Forest Genetics Research Program Slash Pine Polymix Trials

Abstract

The Cooperative Forest Genetics Research Program (CFGRP) has completed polymix test installation for the second generation of slash pine (White, et al. 1993).The objective of this testing is to evaluate the general combining ability of advanced generation slash pine selections for rust resistance and individual tree volume. The eight tests comprising Polymix Series I were established in the winter of 1997-1998 and contain 139 polymix families. The field design for this test series was randomized complete block with twenty blocks of single-tree plots per location. Great care was taken in selection and silvicultural treatment of these sites. The resulting age-five single-tree heritabilities for rust resistance and individual tree volume were 0.26 and 0.30, respectively. These heritabilities are from twice to three times those realized from first generation tests at the same age. The differences between heritabilities across generations result from better silvicultural treatment which provided a more uniform environment and faster growth, and from a better field design which positioned the offspring more efficiently across the environment. Increases in the heritability of rust resistance are most probably due to the uniform environment for growth. The more uniform environment also affected the difference between filler and non-filler microsites making the types of microsite appear less different than was previously assumed.