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Pacific Pests, Pathogens & Weeds - Mini Fact Sheet Edition

Taro corm rots - post-harvest (179)

Photo 1. The dry white crumbly rot at the bottom of the corm is caused by Pythium splendens. The pinkish tissues above and slightly to the right are a reaction to infection by the corm tissues. The white semi-circle on the left is the cottony growth of Athelia rofsii.

Photo 2. Light brown firm rot caused by Phytophthora colocasiae. The rot on the lower left side is caused by Athelia rolfsii. The corm has been incubated at high humidity overnight to stimulate the growth of the fungus.

Photo 3. Light brown firm rot in a taro corm caused by Phytophthora colocasiae, after about 8 days.

Photo 4. Black spongy rot caused by Lasiodiplodia theobromae. These rots usually follow those of Pythium and Phytophthora, or they come in later after the corms have started to lose moisture.

Photo 5. These two corms have been in a plastic bag for 4 weeks; the one on the left is still healthy whereas the one on the right has been destroyed by the soft rot bacterium, Erwinia chrysanthemi.

Summary

Worldwide in the tropics, on many crops. Important diseases.
Fungi, water moulds (oomycetes) and bacteria cause the rots. They enter corms at harvest when suckers are broken off. The common ones are: (i) Athelia – pink with white border; (ii) Pythium - white crumbly rot; (iii) Phytophthora taro leaf blight - firm brown rot; (iv) Lasiodiplodia - black, spongy, sour-smelling rot; and (v) Erwinia - soft rot.
Cultural control: harvest, remove suckers and soil, and store in (i) leaf-lined soil pit, or (ii) plastic bags or (iii) plastic-lined cardboard boxes, if for markets.
Chemical control: improve storage in plastic bags by first dipping corms in bleach (1% for 1-2 mins).

Common Name

Taro corm rots (post-harvest)

Scientific Name

The following are the commonly recorded rots that develop in taro corms after harvest:

Athelia rolfsii (see Fact Sheet no. 11)
Lasiodiplodia (Botryodiplodia) theobromae
Pythium splendens
Phytophthora colocasiae (see Fact Sheet no. 14)
Erwinia species: Erwinia carotovora subsp. carotovora (see Fact Sheet nos. 101, 214, 296), and Erwinia crysanthemi.

AUTHOR Grahame Jackson

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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