Species differences in early growth and rust incidence of loblolly and slash pine

Abstract

Eleven field tests with two silvicultural treatments (intensive and less intensive) with three taxa (improved and unimproved Pinus elliottii and improved P. taeda) were established by the Cooperative Forest Genetics Research Program in the lower coastal plains of the southeast USA. Results from assessment at 3-years-old indicate that P. taeda is consistently taller with less rust incidence than P. elliottii in both intensive and less intensive cultures. The early superiority of P. taeda was only partially due to its lower rust incidence. The more intensive silvicultural treatment increased third-year height growth and also height differences among taxa on all sites. A slight increase of rust incidence was produced by increasing intensive management (29.2–33.6%). The increase in cultural management did not alter the ratios of infection percentages of any two taxa. The ratios of any two taxa, one to another, were essentially constant across all sites and in both silvicultural treatments. Significant genetic gain from breeding for rust resistance was detected at this age for P. elliottii. When 50% of unimproved P. elliottii trees were infected, 36.8% of improved P. elliottii trees were infected. For height growth, improved material was 4 and 8% taller than unimproved P. elliottii in less intensive and intensive treatment, respectively.