Occurrence of Pestalotiopsis uvicola Causing Leaf Spots and Stem Blight on Bay Laurel (Laurus nobilis) in Sicily.

Abstract

In the spring of 2004, during a disease survey in three nurseries of eastern Sicily, a new leaf and stem problem was observed on 20 to 40% of young (2- to 6-month-old) container-grown bay laurel (Laurus nobilis L.). Affected plants exhibited sporadic water-soaked leaf spots on leaf edges that subsequently enlarged and turned into necrotic lesions. These spots were always bordered by a dark brownish margin. Frequently, these necrotic lesions expanded into stems causing blight of young shoots. No symptoms were observed on 2- to 3-year-old plants. Small portions (1 to 2 cm) of symptomatic tissue were surface disinfested for 30 s in 1% NaOCl, rinsed in sterile distilled water, placed on potato dextrose agar (PDA), and incubated at 22 ± 2°C. A fungus consistently isolated from affected tissues was identified as Pestalotiopsis uvicola (Speg.) Bissett based on morphological characters (1). Acervular conidiomata (as much as 250 μm in diameter) appeared in cultures on PDA at 24 ± 2°C over a period of 13 days. All isolates had 4-septate fusiform to narrow ellipsoid conidia with 2 to 4 apical appendages, often aggregated, and averaging 8 μm long. Conidia ranged from 20 to 25 μm long and 6 to 7 μm wide. Basal appendage was single, attenuated, and as much as 3 μm long. Three isolates of P. uvicola were selected for pathogenicity tests. Leaves and stems of 6-week-old seedlings of bay laurel were lightly wounded with a hypodermic needle, and a PDA mycelial plug (5 mm in diameter) was placed on the surface of wounded tissues. Sterile agar plugs were placed on control plants. This method was used to inoculate 6 plants for each isolate. All plants were incubated at 95 to 100% relative humidity and 25 ± 1°C. After 7 days, leaf spots and necrotic lesions on the stem similar to those observed in nurseries were observed. Control plants remained symptomless. Koch's postulates were fulfilled by reisolation of the fungus from affected tissues. Although found in only a few nurseries, the infections could be a threat to an important production area of bay laurel in Sicily. To our knowledge, this is the first report of P. uvicola on bay laurel in the world. Reference: (1) T. R. Nag Raj. Mycotaxon 26:211, 1986.