General And Specific Combining Ability For Fusiform Rust Infection In Slash Pine

General and specific combining ability for fusiform rust infection were calculated on a number of five and ten year old slash pine genetic tests. Average family heritability for rust infection at a single location was 0.54 at age five and 0.53 at age ten. General combining ability accounted for 81% of the genetic variation at both ages. Coefficients of genetic prediction between ages five and ten were 96% as large as age ten heritabilities indicating that selection at age five would be as efficient as delaying selection until age ten. Age five family heritabilities calculated for one set of parents classified as resistant at the USDA Forest Service Resistance Screening Center (RSC) averaged 0.33 across three tests with only 52% of the genetic variation attributable to general combining ability. This could be a sampling artifact caused by low infection levels as the susceptible checklots averaged only 31.7% infection. However, it is possible that screening at the RSC changed the population structure. If so, using variance components from control-pollinated genetic tests of unscreened parents to plan subsequent breeding strategies or to predict gains for parents screened at the RSC is inappropriate. Resolution of this question will require more field tests of parents classified as resistant to fusiform rust at the RSC.

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Author(s): Thomas D. Byram, William J. Lowe

Publication: Tree Improvement and Genetics - Southern Forest Tree Improvement Conference - 1995