GENETIC PARAMETER ESTIMATES FOR RESISTANCE TO RUST (CRONARTIUM-QUERCUUM) INFECTION FROM FULL-SIB TESTS OF SLASH PINE (PINUS-ELLIOTTII), MODELED AS FUNCTIONS OF RUST INCIDENCE

Data from 171 slash pine progeny tests, incorporating over 700 differe nt families from more than 2100 first-generation parents and approxima tely 170000 trees, were used to estimate variance and covariance compo nents by Restricted Maximum Likelihood (REML) in both single-site and paired-site analyses. From these REML estimates, genetic parameters (h eritabilities, proportion of dominance, type B genetic correlations, a nd age-age genetic correlations) were estimated for resistance to fusi form lust infection at 4 to 15 years of age. Predictive models were de veloped for biased (single-site) heritability, unbiased (paired-site) heritability and the type B genetic correlation. Biased heritability e xhibited a maximum of 0.20 at an average rust infection of 72%. Unbias ed heritability estimates from paired-site analyses increased linearly with increasing average rust infection in the tests; however, in very few test pairs did the average rust infection exceed 75%, and extrapo lation beyond 67% would be unreliable. Although genotype-environment i nteraction was present, it was of little consequence except at low rus t infection levels. The proportion of dominance variance (when compare d to the total phenotypic variance) was not related to rust infection levels or age, and across all tests and ages averaged 0.087 and 0.053 in single-site and paired-site analyses respectively. Since dominance variance was small relative to additive variance, except when rust inf ection levels were low, it was considered to be of little practical im portance. Test age was not a significant factor affecting any genetic parameter examined, and all age-age genetic correlations were near +1. 0. The results endorse the current breeding strategy, which is based o n recurrent selection for general combining effects, and stresses the importance of restricting improvement efforts to sites with moderate t o high rust infection levels.