Phytophthora colocasiae
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Author(s): Scot Nelson, Hawaii
Source: Flickr
Phytophthora colocasiae Racib. 1900 - (taro blight)
The oomycete is widespread in tropical parts of Asia, Australia/Pacific and Africa. It infects taro, Colocasia esculenta, and some closely related plants. The symptoms include brownish leaf spots, often with chlorotic halos and shot hole lesions. These enlarge, become zonate and result in leaf rot. Orange or reddish brown exudates may appear at the infection site. Petioles and corms also become infected. The disease is airborne and spreads through rain splashes. It can quickly reach epidemic levels under suitable conditions and yield reductions of 50% or more have been reported for susceptible cultivars. The disease persist in the environment in plant debris or as durable spores. Using resistant cultivars is the most appropriate management approach. Cultural control like destroying infected plants is also recommended. Chemical control may be suitable under certain conditions.
The sporangia are produced on the leaves and are egg-shaped to elliptical with a distinct narrow apical plug. They are approximately 40-50 x 20-25 µm large. The sporangia disperse through water and can germinate directly or release zoospores. Thick-walled chlamydospores have been observed in culture and have a diameter of about 25 µm. The pathogen is heterothallic, requiring the mating types A1 and A2 for sexual reproduction. Oospores have a diameter of around 25 µm.
- Other images of Phytophthora colocasiae (IPM Images - click to enlarge)
symptoms on taro leaf
sporangia
release of zoospores
germinating zoospores
