Stability of Rust Infection Ratios for Resistant and Susceptible Slash and Loblolly Pine Across Rust Hazard Levels
Abstract Fusiform rust resistant and susceptible loblolly and slash pine (bulk mixes of six parents each) were planted at six locations. The ratio of resistant-to-susceptible seedlot infection in both species was stable across all levels of rust hazard across all locations. In other words, the percentage of infected trees in the resistant seedlot was essentially a constant fraction of the percent infection in the susceptible seedlot. The resistant-to-susceptible seedlot infection ratio was 0.225 for loblolly pine and 0.371 for slash pine. For slash pine, predicted breeding values for rust resistance were used to make an accurate prediction of this ratio. The pattern of constant proportional resistance of particular seedlots can be used by forest managers to make planting decisions and assess economic benefits of planting genetically improved material. The results suggest that resistant stock planted at any location will have less fusiform rust infection than would unimproved stock. South. J. Appl. For. 17(4):188-192.