VIEW ARTICLE

Effect of Differential Selection Pressure on Fusiform Rust Resistance in Phenotypic Selections of Slash Pine. R. E. Goddard, Associate Professor of Forest Genetics, School of Forest Resources and Conservation, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611; R. A. Schmidt(2), and F. Vande Linde(3). (2)Associate Professor of Forest Pathology, School of Forest Resources and Conservation, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32611; (3)Research Forester, Brunswick Pulp Land Company, Brunswick, Georgia 31520. Phytopathology 65:336-338. Accepted for publication 10 October 1974. DOI: 10.1094/Phyto-65-336.

Progenies (families) or open pollinated Pinus elliottii var. elliottii representing high and low selection pressure for resistance to Cronartium fusiforme were evaluated in a high-rust incidence planting. Frequency distributions of percent rust by family show that these two populations are distinctly different with regard to rust susceptibility. The population of families from selections of the tree improvement program (low selection pressure) is mostly highly susceptible and is approximated by an increasing exponential function with an average disease percentage of 85.1. The population of families from rust-free selections from a heavily infected plantation is relatively resistant and is normally distributed with an average disease percentage of 61.2. These data suggest that phenotypic selection of rust-free trees from areas of high rust incidence can provide significant gains in resistance of slash pine to fusiform rust.