A comparison of non-improved provenances and improved checklots from a Pinus taeda breeding program

This study compared non-improved, wild seed sources of Pinus taeda L. from provenances in the southeastern United States to improved checklots developed from first-generation selections from non-improved plantations (plus trees). Provenance variation among the non-improved sources showed similar patterns to the improved checklots, with sources from warmer Coastal regions growing faster. The South Carolina Coastal Plain provenance, which was notably missing from previous provenance studies, exhibited the fastest growth among non-improved provenances. Variation in fusiform rust disease incidence and stem form traits were present. The improved checklots had remarkable gains for stem straightness compared to their non-improved counterparts, apparently due to the intense selection pressure for straightness when choosing plus trees, as well as the strong heritability of the trait. Gains for resistance to fusiform rust disease were modest when comparing improved to non-improved. Growth gains were not detected because the improved checklots were offspring of plus trees with average breeding values for growth. The relative performance of checklots was stable across test sites for growth and stem defect traits, although the trial design avoided testing Coastal sources in the colder test sites where maladaptation was expected. The checklot means for growth, disease resistance, and straightness from this study (where genetic entries were tested side-by-side) were strongly correlated to breeding values estimated from progeny tests, which depended on indirect comparisons from disconnected series. The results highlight the importance of extensive provenance sampling for understanding geographic variation and demonstrate the outstanding improvement in stem form from first-generation selections of P. taeda.