Taro leaf blight (Phytophthora colocasiae): a new disease in Puerto Rico.
During December 2004, a type of blight was found affecting leaves of cultivated taro (Colocasia esculenta) in the sector of Quebrada Arenas, within the municipality of San Lorenzo, Puerto Rico. Symptoms are circular to olive green spots on the upper leaf surface; these appear to be darker, water-soaked or greasy spots on the underside. Infection commonly begins on the lobes and the sides of the leaves where water often collects. As the disease develops, the spots enlarge and become irregular in shape. Spots sometimes turn dark brown with a yellow margin and concentric circles; there may be a clear amber fluid that exudes from the centre of the spots. The exudate becomes dark brown and hard after drying. White powdery masses of spores are often produced around the lesions. Leaf blades are sometimes completely rotted, but do not drop from petioles. Rot spots are usually long, brown and occur anywhere in the petioles. The causal agent was identified as Phytophthora colocasia based on its growth in selective media and by pathogenicity tests. This is thought to be the first report of taro leaf blight in Puerto Rico.