Correlations between pure and hybrid combining abilities of slash pine parents

Abstract

Four trials were analysed to provide taxa comparisons for growth and stem quality as well as genetic parameters for Queensland bred Pinus elliottii (PEE) and Pelliottii x Rcaribaea var. hondurensis (PcH) Fl hybrids. Of particular interest was the genetic correlation between related progenies in pure species and hybrid combination (r,,J, or equivalently the correlation between the general combining ability (GCA) and general hybridising ability (GHA). PEE families produced less volume than either the PCH controls or the F, hybrid families and exhibited slightly more crown defects than either of the other two taxa. The heritability estimates were very high for the Fl hybrid trials but moderate to low in the pure PEE trials. Type-B genetic correlations were high within the same taxa giving further evidence of the low levels of genotype by environment interaction found within southeast Queensland for these two taxa. Pearson correlations between univariate GCA and GHA estimates provided similar r,, estimates to those obtained directly from multivariate analyses. There was no correlation between the GHA and GCA estimates for the 56 PEE parents represented in this study for growth traits; however, a high and positive correlation was found for straightness. While straightness in hybrids may be selected for using pure PEE progeny trial data, growth traits in pure and hybrid progeny of PEE appear to be uncorrelated. Field testing of Fl hybrid families or poly-crossed PEE parents prior to operational deployment or inclusion in more intensive clonal screening programs will continue to be necessary if resources are to be focused on the very best hybrid families.