First Report of Stem Bleeding and Trunk Rot of Kentia Palm Caused by Thielaviopsis paradoxa in Italy.

Abstract

The Kentia palm or Sentry palm (Howea forsteriana (C. Moore & F.v. Muell.) Becc.) is one of the most popular palms in the world. In Italy, it is suitable for growing indoors or outdoors. In September 2006, bleeding was found on the stem of a 20-year-old Kentia palm growing in a field nursery in eastern Sicily. The trunk began to bleed from cracks or fissures of the bark at 5 ft (1.5 m) from the ground level. Tissues surrounding the stem cracks were black. The plant canopy showed no symptoms. Cross-sections revealed brown rot confined to one side of the trunk where the rot was spreading inward from the surface. Infected tissues did not emanate odor of fermented fruit. Internal tissue adjacent to the rotted areas was placed on carrot agar amended with 500 μl of streptomycin sulphate and acidified (lactic acid; pH = 3.6) potato dextrose agar (PDA). A transverse section of affected palm tissues was maintained in a moist chamber for 6 days. Microscopic examinations of isolates obtained on media and sporulation from affected tissues yielded Thielaviopsis paradoxa (De Seyn.) Höhn (2). Endoconidia, measuring 3.9 (range 3 to 6) × 8.2 μm (range 6 to 14) (n = 50), were cylindrical to somewhat oval when mature, hyaline to brown, and smooth walled. Endoconiodophores were usually straight, colorless to pale brown, as much as 150 μm long, with a terminal spore-bearing cell through which spores are borne. Chlamydospores were smooth, thick walled, brown, in chains, and were 8.8 (range 5.5 to 15.0) × 15.8 μm (range 9.0 to 25.0) (n = 50). Koch's postulates were fulfilled by stem inoculation on a 20-year-old double-stem Kentia palm growing in the same field nursery. Ten mycelial plugs (5-mm diameter) obtained from 14-day-old single-spore colonies growing on PDA at 24°C were applied to 10 5-mm-diameter stem wounds. The same number of inoculations was used as a control in the other stem and treated with sterile agar plugs. Following inoculation, the mycelial plugs and the stems were wrapped with Parafilm. After 20 days, stem rots were detected only on the inoculated stem wounds, and stem bleeding was observed after 3 months. The pathogen was reisolated from symptomatic tissues. A Thielaviopsis sp. was previously reported in Florida on Kentia palm as being responsible for a frond necrosis (1). While stem bleeding seems to be a common symptom on coconut (Cocos nucifera L.), it is not commonly reported on other palm species. Only recently, T. paradoxa was detected for first time in Sicily on date palm imported from Egypt (3). To our knowledge, this is the first record of stem bleeding caused by T. paradoxa on palms in Italy, and the first record of stem bleeding and stem rot on Kentia palm.