Invasive Species Compendium

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Abstract

First report of bacterial leaf spot caused by Pseudomonas cichorii on Phlox paniculata in Italy.

Abstract

During the spring of 2003 and 2004, leaf spot symptoms were observed in autumn phlox (Phlox paniculata) plants in some private gardens in the Biella area of northern Italy. Lesions were first observed on leaves at the collar level and later on the entire plant. Lesions started as water-soaked areas, which in few days developed on the upper side of the leaves into irregular, shrunken, reddish brown spots from 1 to 2 mm in diameter. Lesions on the lower surface sometimes had a translucent halo. In many cases, the leaves were completely withered. Disease was particularly severe during the spring and autumn and its incidence ranged from 10 to 25%. No fungal structures were observed within the lesions. SDS-PAGE and pathogenicity assays using isolates from infected plants identified the causal agent as Pseudomonas cichorii. This is thought to be the first record of bacterial leaf spot of Phlox paniculata in Italy as well as in the world.