A survey of foliar fungal endophyte communities of Rocky Mountain bristlecone pine populations in the Colorado Rocky Mountains
Date
2017
Authors
Albertson, Alyssa, author
Bedinger, Patricia, advisor
Kassenbrock, C. Kenneth, advisor
Stewart, Jane E., committee member
Schoettle, Anna W., committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Rocky Mountain bristlecone pine (Pinus aristata) is an exceptionally long-lived charismatic tree species found at high elevations in the southern Rocky Mountains of Colorado, New Mexico, and Arizona (Fryer, 2004). This species has recently come under threat from the disease white pine blister rust (WPBR). White pine blister rust is caused by the pathogenic fungus Cronartium ribicola, which was inadvertently introduced into North America from Europe in the early 1900's, and has since spread widely with devastating impacts (Burns et al., 2008). In North America, WPBR is largely lethal to five-needle pine species. In Colorado, WPBR has been found in stands of Rocky Mountain bristlecone pine and limber pine (Pinus flexilis), and efforts have been made to identify trees with increased resistance to the disease. The USDA Forest Service Rocky Mountain Research Station has identified specific trees that harbor some level of heritable resistance to WPBR, versus those appearing fully susceptible (Schoettle, 2004; Schoettle et al., 2012; Schoettle et al., 2014). Essentially all plants in the wild harbor endophytic bacteria and fungi, which are defined as co-existing in plant tissues without causing evidence of disease, and it is increasingly appreciated that endophytes can alter plant responses to both biotic and abiotic stresses (Rodriguez et al., 2008). It has been reported that fungal endophytes can enhance resistance to blister rust in western white pine (Pinus monticola) (Ganley et al., 2008). The endophytic fungi of Rocky Mountain bristlecone pines have not been previously studied. We used two techniques to survey the endophytic fungal communities present in wild populations of resistant and susceptible bristlecone pines. The first technique was to isolate endophytic fungi by culturing surface-sterilized pine needles. The second technique was to extract DNA from the pine needles, and use PCR amplification of fungal-specific sequences, followed by high-throughput Next Generation sequencing (NGS) to identify and quantify fungi present, regardless of whether or not they could be cultured. By culture we recovered 259 fungal isolates that were placed into 81 morphological groups, whereas the NGS returned 42,003 useable DNA sequences that were grouped into 791 operational taxonomic units (OTUs). The two techniques used in this study had significant overlap; most of the cultured fungi were also identified in the NGS data set. The high throughput sequencing data also revealed differences between the endophyte populations of trees previously inferred to have or lack resistance to white pine blister rust at each location. Further research will be needed to understand whether endophytes may modify, slow, or even prevent infection by the pathogen C. ribicola.