The Ecology and Genetics of Eastern Hemlock and Fraser Fir Threatened by Invasive Adelgids.
Thomas AM. 2021. The Ecology and Genetics of Eastern Hemlock and Fraser Fir Threatened by Invasive Adelgids.. North Carolina State University
ABSTRACT Chapter 4: The balsam woolly adelgid, Adelges piceae, Ratzeburg (BWA), was first reported on Fraser fir, Abies fraseri, (Pursh) Poir., on Mount Mitchell in North Carolina in 1955. A novel herbivore in North America, BWA was responsible for sharp declines in wild Fraser fir populations throughout its Southern Appalachian distribution during the 1960s and 1970s. Fraser fir is also the premier Christmas tree species in North Carolina and plantations require frequent pesticide applications to prevent BWA related damage and mortality. Breeding Fraser fir for BWA tolerance or resistance traits may lessen or eliminate the need for pesticide treatments in the future. This genetic study evaluated 37 clones of improved Fraser fir for increased tolerance or resistance to BWA using tree growth, gouting, loss of apical dominance, systemic rotholz formation, and mortality as performance metrics. Additionally, we evaluated the lateral bud transcriptome of select clones in response to BWA feeding via RNA-Seq. We found a broad range of responses among clones ranging from extreme susceptibility to putative resistance. Significant differential expression of genes related to a phloem feeding insect (PFI) response and associated SA signaling, along with upregulation of genes related to guaiacol synthesis, IAA inactivation, and cell wall remodeling, were found only in putatively resistant clones. We believe these data provide strong evidence that some degree of BWA resistance is present in Fraser fir populations which could be further enhanced through selective breeding.