Characterization of Diaporthe spp. Associated With Spruce Decline on Colorado Blue Spruce in Michigan

• Published in: Phytopathology 2021-03, Vol.111 (3), p.509-520
• Main Authors: Sakalidis, Monique L, Medina-Mora, Carmen M, Shin, Keumchul, Fulbright, Dennis W
• Format: Article
• Language: English
• Subjects: Ascomycota; Colorado; Michigan; Phylogeny; Picea; Plant Diseases
• ISSN: 0031-949X; 1943-7684
• DOI: 10.1094/PHYTO-08-19-0287-R

Since 2006 there has been a decline in Colorado blue spruce (CBS; ) planted as landscape trees and for Christmas tree production throughout the Lower Peninsula of Michigan. This decline is characterized by a slow loss of needles in the lower portion of the tree starting at branch tips, followed by entire branch dieback, which progresses upward over several years. This dieback has been linked to shallow branch cankers visible in the phloem when the bark layer is removed. Isolates in the fungal genus have been consistently isolated from lesion margins on symptomatic branches. Before the initial reports of declining CBS in landscape and Christmas trees, was known only as a nursery disease of CBS. To determine the species of linked to the decline of CBS in Michigan, seven gene regions were sequenced from a collection of isolates collected in 2011 through 2018 from CBS and other coniferous hosts. Subsequent phylogenetic analyses indicated that and a novel clade were present on symptomatic CBS in Michigan. The new species nov. is described, and Koch's postulates were confirmed for nov. and . nov. produced the largest cankers in greenhouse pathogenicity trials, and dual inoculations of nov. and produced intermediate cankers.