Cercosporidium sequoiae isolated from Cupressus lusitanica in Saint Lucia

Cupressus lusitanica (Mexican white cedar) is an important ornamental crop used in landscape plantings, windbreaks and for Christmas trees. In July 2005, a new disease was found on Cupressus lusitanica, in St Lucia. A progressive browning of the rachis from the lowest branches upwards was observed (Fig. 1). The oldest needles close to the stem were the first to become infected with the disease spreading upwards out along the branches until only the tips remained green (Fig. 2). Severely infected plants eventually died, especially when subjected to drought stress. These symptoms were seen in both nurseries and established plantations at three different sites on the island. Roots, stems and needles were sent to the Global Plant Clinic (UK) for analysis.

Under microscopic examination, greyish-black tufts (fruiting structures) were clearly seen on the browned needles. Conidiophores were brown, simple, flexuous, with thickened scars and occurred in dense fascicules. Conidia were pale brown, narrowly oboclavate, straight or slightly curved, obtuse at the apex, verruculose 2-5 euseptate, bearing a thickened hilum at the base, 25-61 µm in length (47 µm) and 3-7 µm wide (4.5 µm) (Fig 3). Based upon these characteristics, the fungus was identified as Cercosporidium sequoiae (Baker et al., 2000).

This is an important finding as Cercosporidium sequoiae is the causal agent of cercosporidium blight, a serious disease on a wide range of coniferous plants (Leahy, 2000). The host range includes the ornamental shrub Thuja orientalis, which is also grown on St Lucia and the surrounding islands. Conidia of C. sequoiae may be spread naturally by wind and water splash. Disease development is favoured by warm, humid, wet weather or by overhead irrigation (Leahy, 2000). To our knowledge this is the first report of Cercosporidium sequoiae on Cupressus lusitanica in St Lucia.