First Report of Bacterial Leaf Spot Caused by Pseudomonas cichorii on Phlox paniculata in Italy

Plant Disease
A GaribaldiM L Gullino

Abstract

Phlox paniculata L. (fall phlox) is a perennial garden species belonging to the Polemoniaceae family. During the spring of 2003 and 2004, leaf spot symptoms were observed on fall phlox plants in some private gardens in the Biella area (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 fall and its incidence ranged from 10 to 25%. No fungal structures were observed within the lesions. Small fragments of tissue from affected leaves were macerated in nutrient yeast dextrose broth (NYDA), and dilutions of the resulting suspension were streaked onto NYDA and potato dextrose agar (PDA). Isolations were made from at least 25 leaves. Plates were maintained at 22 ± 1°C for 48 h. No fungi were isolated from the spots on NYDA or PDA. Colonies typical of Pseudomonas species were consistently isolated on NYDA. Isolates were negative for levan, potato...Continue Reading

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