Genetic Parameter Estimates from a Polymix Breeding Population of Pinus taeda L.

Estimation of genetic parameters from progeny testing is essential for many important decisions in forest tree breeding. In this study, we estimated heritabilities, trait-trait genetic correlations, and genotype by environment (GxE) interactions using a large multi-environmental data set of Pinus taeda L. in the southern United States. In the study, 284 parents were pollinated with a pollen mix and were field tested in four different test series. A total of twenty tests (two to seven tests per series) were established using randomized complete block design with single tree plots. Half-sib family-mean heritability estimates within individual test series varied considerably for all the traits. Pooled estimates of half-sib family-mean heritability estimates across series were 0.81 for fusiform rust incidence; they were relatively lower for tree height (0.68), diameter at breast height (DBH; 0.66), and stem straightness (0.58). Genetic correlations between pairs of traits were low except for height and diameter, which had a high genetic correlation (0.79). Additive genetic correlations between pairs of sites within test series (as a measure of GxE) varied. The pooled estimates ranged between 0.65 (DBH) to 0.80 (fusiform rust). The results suggest that polymix mating is efficient for parental selection in Pinus taeda L. and for deployment in the seed orchards. Study Implications: This study focused on genetic variation in the Piedmont breeding population of Pinus taeda L. in the United States. The Piedmont population was developed for more inland and colder regions of the species. Fusiform rust disease incidence of pine species of southeastern United States is a major threat to pine plantations. Understanding the level of genetic control on disease outcome is vital to develop sound breeding strategies and recommend deployment practices to mitigate the economic loss of landowners. The results provide valuable information to breeders to select disease-resistant genotypes to breed and put into seed orchards to mass-produce stock for planting.