Realized Genetic Gains of Rust Resistant Selections of Slash Pine (Pinus elliottii var. elliottii) Planted in High Rust Hazard Sites

Realized gains from selection for resistance to the fungal disease fusiform rust caused by Cronartium quercuum f. sp. fusiforme were estimated using data from five field trials planted on large rectangular plots in high rust-hazard sites. These five realized gain trials, planted as a Best Management Practices study (BMP), compared resistant and susceptible mixtures of families from the first-generation breeding population of slash pine (Pinus elliottii var. elliottii Engelm.) in southeastern North America. Analyses of variance (Proc Mixed using REML in SAS), conducted to test the significance of realized gains and interactions contrasting resistant with susceptible seedlots, detected important and highly significant realized gains in both rust resistance and mid-rotation yield. Significant gains were obtained for rust resistance at age 5 and stand yield at age 16 with high stability across sites and across silvicultural treatments, indicating that gains in rust resistance and the associated influence on gains in stand yield were consistent under many environmental conditions. Additionally, the values of realized gains in stand yield steadily increased with age, primarily due to increased rust associated mortality with age in the susceptible material. The 25% realized gain for rust resistant material compared to rust susceptible material obtained at age 16 was conservatively extrapolated to a 25-year-old rotation-age gain of 51.4 m³ ha^-1 (735 feet³ acre^-1) in inside-bark volume.