Abstract
Damage or mortality from pathogens can reduce productivity of forest plantations, as well as significantly harm natural forest ecosystems. Genetic resistance within the host species is the first line of defense for tree species. Resistance breeding programs for the native fusiform rust and exotic (to North America) white pine blister rust diseases are two of the longest concerted efforts in forest trees, spanning more than 50 years. Advances in developing greater genetic resistance have been made in both pathosystems, but unique challenges and opportunities in each system translate to different approaches. Fusiform rust resistance programs have mainly emphasized complete resistance, while partial resistance plays a prominent role in white pine blister rust resistance programs. Advances in the development of molecular genetic tools now permit investigations in conifers and their associated rust pathogens. Good progress has been made in identifying resistant populations and understanding resistance in these pathosystems, and resistant stock is now being used extensively for reforestation and restoration. These programs represent great success stories brought to fruition by the long-term efforts. However, continued support will be needed to enhance the level and fully realize the potential of durable genetic resistance in these invaluable North American conifer species.
Highlights
Rust diseases of forest trees have large economic and ecological impacts in North America
Due to a combination of white pine blister rust and mountain pine beetle outbreaks, whitebark pine has been proposed for listing under the Endangered Species Act in the U.S [5], and similar concerns are present in Canada where it is protected under the federal Species at Risk Act (SARA)
The basic steps involved in resistance breeding programs in forest trees include: (1) selection of candidate trees; (2) collecting seed from the candidate trees to use in short-term artificial inoculation resistance testing; (3) characterizing the types of resistance; (4) selecting the top families and individuals within families and/or selecting the best parents for orchards based on their progeny performance for developing seed orchards and for breeding to increase resistance; (5) establishing field trials to directly assess resistance or to confirm the results of artificial inoculation trials and examine durability of resistance; and (6) operational use of resistant seedlings for reforestation or restoration
Summary
Rust diseases of forest trees have large economic and ecological impacts in North America. (Pinus taeda), slash (P. elliottii) and longleaf (P. palustris) pines are important components in native ecosystems as well as extremely valuable economically as the major species in large-scale, managed plantations in the southeastern United States. In these species, the fusiform rust pathogen The southern pine-FR pathosystem is native and presumably co-evolved Silvicultural practices such as the large-scale establishment of even-aged pine plantations and intensive management including fertilization and fire suppression has led to increases in the abundance of some species of oaks, the native alternate hosts of C. quercuum f. We will focus primarily on the WPBR resistance programs involving western white pine, and the FR resistance programs involving loblolly pine and slash pine where the most concerted efforts have occurred since the 1960s
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