Arboriculture & Urban Forestry 44(3): May 2018 Disease Description Three drippy-blight-diseased trees measuring 50–75 cm diameter at breast height located in Boulder, Colorado, parks were felled in Decem- ber 2010. Approximately 100 twigs <1 cm diam- eter were collected from each tree, and evaluated for the presence of kermes scales and cankers. In 2015 and 2016, diseased trees throughout Boulder were monitored weekly from May to October to document the disease progression. RESULTS AND DISCUSSION The red oak (NCCB100490) and pin oak (NCCB100489) isolates of L. quercina subsp. quercina, shared 100% of nucleotide identity when the four gene sequences were compared (Caballero et al. 2014), and formed a monophy- letic clade with L. quercina subsp. quercina ATCC 29281, based on the multi-locus sequence analy- sis (Figure 2). The Colorado strains are closely related to, but genetically distinct from, L. quer- cina subsp. quercina ATCC 29281 found in Cali- fornia. Strains are less closely related to L. quer- cina subsp. iberica (LMG 26264T, LMG 26265, LMG 26266, R-43277) or L. quercina subsp. bri- tannica (LMG 26267T, LMG 26268, LMG 26269, 149 R-43661, LMG 6054). Lonsdalea quercina subsp. iberica causes bark cankers and drippy bud on holm oak and Pyrenean oak in Spain (Q. ilex and Q. pyrenaica, respectively) (Biosca et al. 2003; Poza-Carrión 2008), whereas in the United King- dom, L. quercina subsp. britannica is thought to contribute to acute oak decline of Q. robur and Q. petraea (Brady et al. 2012; Denman et al. 2012). Oozing bark cankers on hybrid poplar (Populus × euramericana) have been attributed to L. quer- cina subsp. populi (Tóth et al. 2013; Li et al. 2014). Following inoculation with L. quercina subsp. quercina, canker development associated with copious production of bacterial exudates was noted in tested trees involving all three red oak species (northern red, pin, and Shumard), except for one of eight Shumard oak saplings. Lonsdalea quercina subsp. quercina was consistently re-iso- lated from canker margins on each oak species. Trees inoculated on leaf whorls exhibited bac- terial ooze within five to seven days of inocula- tion (Figure 3a), and small lesions formed as the shoots elongated. Shoot and leaf dieback were also observed. Cankers on red oak were signifi- cantly longer than cankers on pin oak (P = 0.04), with lengths of 1.02 cm and 0.55 cm, respectively. Shumard oak cankers measured 0.77 cm and did Figure 2. Phylogenetic tree of Enterobacteriaceae species based on 16S ribosomal RNA, DNA gyrase subunit B genes (gyrB), beta subunit of ATP synthase (atpD), and translational initiation factor genes (infB) sequences. A Bayesian analysis was performed for 500,000 generations using a GTR / gamma distributed with invariant sites model of evolution. Bayesian probabilities are shown next to each branch. Species: Cronobacter sakazakii; Erwinia piriflorinigrans (CFBP 5882); Lonsdalea quercina subsp. iberica (LMG 26264T, LMG 26265, LMG 26266, R-43277); Lonsdalea quercina subsp. quercina (red oak isolate NCCB100490, pin oak isolate NCCB100489, ATCC 29281); Lonsdalea quercina subsp. britannica (LMG 26267T, LMG 26268, LMG 26269, R-43661, LMG 6054); Pantoea calida; and Erwinia toletana. ©2018 International Society of Arboriculture
May 2018
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