Disease resistance in whitebark pine and potential for restoration of a threatened species

Societal impact statement Forests world‐wide are being negatively affected by non‐native, invasive pathogens and pests, and some tree species face uncertain futures. To retain these species as components of future forests, the rare genetic resistance that exists needs to be identified and harnessed. The applied tree improvement program for whitebark pine (Pinus albicaulis), a threatened (in the United States) and endangered (in Canada) keystone species in many forests in western North America, provides an example of what can be accomplished in a relatively short timeframe. The level and frequency of resistance vary by location, and this information will be used to implement the national restoration plan. Summary Forest trees face serious threats from non‐native diseases and pests, often causing high mortality of both the existing trees and regeneration. Developing populations with genetic resistance can help restore forests and retain affected species. Resistance programs have historically focused on species of high economic importance; however, the threats to species of little direct economic value that provide other important ecosystem services are also great. We examined the frequency, level, and geographic variation in genetic resistance to white pine blister rust in the threatened Pinus albicaulis (whitebark pine), a keystone species in high‐elevation ecosystems in western North America. In the two trials reported here, 2‐year‐old seedling progeny of 225 whitebark pine parent trees were inoculated with two geographic sources of the fungal pathogen Cronartium ribicola and evaluated over 5 years for an array of resistance traits. The trials focused primarily on parent trees from the Oregon and Washington populations. We found unexpectedly high levels of quantitative resistance in some seedling families and populations, in stark contrast to levels observed in similar resistance programs with other North American white pine species such as Pinus monticola and Pinus lambertiana. The level of resistance found in some whitebark pine populations provides optimism about potential recovery efforts for this species. Restoration efforts are underway by government agencies, tribes, and non‐government organizations in both the United States and Canada. These efforts may help boost support for applied genetic resistance programs in other forest tree species severely affected by non‐native pathogens or pests

Genetic Resistance to White Pine Blister Rust in Limber Pine (Pinus flexilis): Major Gene Resistance in a Northern Population

Limber pine, Pinus flexilis, a wide-ranging tree species in western North America, is highly susceptible to white pine blister rust (WPBR), caused by the non-native fungal pathogen Cronartium ribicola. The Canadian populations in particular have been heavily impacted, and in 2014 limber pine was designated Endangered in Canada by COSEWIC. Little is known about genetic resistance to WPBR in limber pine, but major gene resistance (MGR) has been characterized in some populations in the U.S.A. This study examines resistance in seedling families from 13 parent trees from British Columbia, Alberta and Oregon, representing the northern and northwestern-most populations. Most families were susceptible with 100% of the seedlings cankered, but one family from Alberta segregated 1:1 for cankered and canker-free. This is the first report of (a) MGR in Canada of any of the four species of five-needle pines native to Canada, and (b) any resistance in limber pine in Canadian populations, and is the northern-most known incidence of putative R-gene resistance in a natural stand of any five-needle pine species. Many of the Canadian selections were from stands with high incidence of WPBR infection, and their high susceptibility in this trial suggests that further infection and mortality is likely in the Canadian populations.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Locations of seed families and geographic distribution of genetic subgroups.

<p>A total of 124 seed families were samples in 16 seed (sub) zones. Each pie chart represents the proportion of genetic subgroups (GG-1 to GG-9) as identified by STRUCTURE in a given area.</p

Association of whitebark pine genetic subgroups with relative levels of disease severity post inoculation by <i>Cronartium ribicola</i>.

<p>(a) Mean values of relative levels of disease severity were shown for seedlings with nine genetic subgroups (GG1 to GG9). Standard error (SE) was calculated based on the entire subpopulation of each genetic subgroup. Statistical difference is significant (T-test and One-way ANOVA test, * <i>P</i> < 0.05, ** <i>P</i> <0.01) between subgroups labelled with different letters.</p

Principal coordinate analysis (PCoA) of whitebark pine populations using GenAlEx version 6.5.

<p>Seed zone (subzone) designations were listed in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0167986#pone.0167986.s001" target="_blank">S1 Table</a>. Three regions are shown by colors, Green: British Columbia (BC), Canada; red: Washington State (WA); blue, Oregon state (OR), USA.</p