Invasive Species Compendium

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Abstract

First report of bacterial leaf scorch caused by Xylella fastidiosa on Gleditsia triacanthos var. inermis in Pennsylvania.

Abstract

In the summer of 2019, three thornless honeylocust trees (Gleditsia triacanthos var. inermis) in Gettysburg (Pennsylvania, USA) were observed in a general state of decline. The trees were 50 to 64 cm in diameter at breast height. Symptoms of the decline included branch dieback, stunted growth, and swollen woody tissues where leaf petioles attached on the branch. Symptoms were randomly distributed in the canopy and progressed from the outer portions of the canopy inward. Based on communication with local arborists who have observed these symptoms on other honeylocusts in the area, from the onset of symptoms, mature, established honeylocust trees died in a period of 3 to 5 years. Bacterial leaf scorch disease, which is caused by the xylem-limited, gram-negative bacterium Xylella fastidiosa, is widespread in Gettysburg on Quercus palustris and Q. rubra. The dieback symptoms and symptom progression on the honeylocust trees are similar to the disease symptoms on the Quercus species. However, the classic scorching symptom was not evident on the pinnately compound leaves. In August of 2019, tissue samples were taken from three symptomatic and two asymptomatic thornless honeylocust trees in Gettysburg. Based on the results of DNA sequence analysis, the causal agent was confirmed as X. fastidiosa. This is thought to be the first report of X. fastidiosa causing bacterial leaf scorch and general decline of G. triacanthos var. inermis in the eastern USA.