Photo 1. Spots of taro leaf blight at the margins and inside the leaf blade. Note that some of the centres of the spots are falling out. Many have a characteristic yellow margin, or halo.
Photo 3. The spore of the water mould, Phytophthora colocasiae, has a characteristic shape to the top (arrow).
Photo 4. Droplets associated with taro leaf blight spots on the underside of the leaf which hardens into pellets as they dry. Leaf spots of other fungi infecting taro do not do this.
Photo 5. The underside of a taro leaf blight spot showing the liquid which "bleeds" from the leaf when it is infected; this liquid dries during the day and becomes hard and dark brown.
Photo 6. The spots are not only very large on this susceptible variety (Niue) in Samoa, but they have joined together to form a blight.
Diagram. Life cycle of Phytophthora colocasiae. Note that the sexual phase of the life cycle has not been seen in Pacific island countries; this is because two mating strains are needed to form the oospore, and only the A2 strain has been found. The oogonium and antheridium are the equivalent to female and male parts which fuse to form the oospore (or resting stage).
Taro leaf blight
AUTHORS Helen Tsatsia & Grahame Jackson
Photos 1&6 Brooks FE (2005) Taro leaf blight. The Plant Health Instructor. DOI:10.1094/PHI-I-2005-0531-01. Diagram Vickie Brewster.
Produced with support from the Australian Centre for International Agricultural Research under project PC/2010/090: Strengthening integrated crop management research in the Pacific Islands in support of sustainable intensification of high-value crop production, implemented by the University of Queensland and the Secretariat of the Pacific Community.
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