Assessing the durability, stability, and usability of genetic resistance to a non‐native fungal pathogen in two pine species

Abstract

Societal Impact StatementDamage to white pine forests by white pine blister rust, caused by the non‐native invasive fungal pathogen Cronartium ribicola, is affecting people across western North America. The loss of white pine forests can impact economic opportunities as well as ecosystem and human well‐being. In this paper we quantify the durability, stability, and usability of natural genetic resistance to the disease in two white pine species using long‐term field trials. By combining quantitative genetic resistance breeding programs with data from field validation trials, land managers and policy makers will be able to better ensure healthy forests for the future. Summary Many tree species are susceptible to non‐native pathogens or pests. Their level of susceptibility can be so severe that they are extirpated, and their use for forest restoration or reforestation is curtailed. Programs to find, enhance, and utilize genetic resistance in tree species are underway. Because trees are long‐lived, resistance must be effective for decades to centuries to be useful. Resistance needs to be durable, stable, and present at a useful level. Field plantings provide the best opportunity to assess resistance durability and stability across a range of environments. In this paper we examine the durability and stability of resistance levels, previously identified in seedling screening trials, of two white pine species, Pinus monticola (western white pine) and P. lambertiana (sugar pine) to white pine blister rust, using eight 15 to 20‐year‐old field trials in Oregon and northern California. We found that resistance varies for each host species and in different environments. Major gene resistance (MGR) may have limited utility and the search for resistance should include all types of resistance, as quantitative disease resistance (QDR) appears to be more durable than MGR in the long term at many sites in our study. Our data provide encouragement and support for the use of long‐term field validation studies in combination with quantitative genetic resistance breeding programs. We advocate for an increased use of field trials to ensure that resistance is effective for restoration and recovery against invasive pathogens and pests.