Fusiform rust, caused by the fungus Cronartium quercum f. sp. fusiforme, is one of the most serious diseases affecting loblolly and slash pines in the southeastern U.S. and causes an estimated $28 million in damages every year. As the primary source of pulpwood and saw timber for the U.S. forest industry, the economic importance of loblolly pine alone to the South and the nation can’t be overstated.
Developing genetic resistance in loblolly and slash pine seedlings is the only realistic way to manage the disease — since chemical control is expensive and impractical — and foresters have used artificial inoculation systems to select for rust-resistant pine families for years. But developing resistant seedlings is complicated by the interactions that take place between the pine host and fungal pathogen at the gene level, where the disease constantly evolves to disarm the resistance genes developed by the tree.
The genetic markers researchers develop to tag resistant genes in loblolly pine breeding populations provide managers with an effective tool to guide tree planting and to determine the best seedlings to grow on a given site. Developing genetic markers relies on decades of genetic research on the complex interactions between the loblolly pine and fusiform rust genomes.
In a recently published article in the journal Forests, scientists from the U.S. Forest Service and North Carolina State University detailed nearly two decades of research on the host-pathogen interaction between loblolly pine and fusiform rust. They describe nine fusiform rust resistance genes they found in loblolly pine, including the specific methods used to locate each gene on the reference genetic map of loblolly pine.
“Understanding how these fusiform rust resistance genes in loblolly pine and other pine-susceptible pines impact resistant screening and the selection of breeding stock is important to tree breeding,” said Dana Nelson, corresponding author of the article and Forest Service Southern Research Station research geneticist. “The documentation of these nine genes provides a key piece of information needed to improve breeding and site selection strategies.”
In 2010, Nelson and others found that gene-for-gene interactions between the pine host and the fusiform rust pathogen largely determine the formation of the galls on stems and branches that weaken and kill infected pines. For the recently published papers, the researchers used this gene-for-gene method to provide the analysis that led to the identification and genetic mapping of the nine fusiform rust resistance genes.
Researchers found that the nine identified genes occur in three groups on the loblolly pine genetic map. “Higher resolution mapping of these and additional resistance genes will lead to better gene testing for breeding programs and maybe someday eliminate the need for costly artificial inoculation testing,” said Nelson.
For more information, email Dana Nelson at firstname.lastname@example.org.