Mosaic Disease of Tapioca: Symptoms and Control Measures

Cassava or Tapioca*

Ø  Cassava or Tapioca (Botanical Name: Manihot esculenta; Family: Euphorbiaceae).
Ø  Cassava is a vegetatively propagated tuber crop plant.
Ø  The root tubers of tapioca are rich in starch.
Ø  Cassava is native to South America. Now the cassava is cultivated worldwide.

Ø  Cassava is a staple food in many regions for about 600 million people worldwide.
Ø  Linamarin is a cyanogenic glucoside found in the roots of cassava plants.

Ø  Linamarin can be converted to cyanide in the gut.

* In fact, tapioca is a starch extracted from the cassava root through a process of washing and pulping. However, the terms ‘Tapioca’ and Cassava are used as synonyms.

Leaf Mosaic Disease of Tapioca

Ø  This disease is commonly known as CMD or Tapioca Mosaic Disease.

Ø  It is one of the worst diseases of tapioca severely affecting the productivity of the plant.

Ø  The disease was first reported in the coastal areas of Nigeria (1929).

Ø  CMD is widely occurring in Kerala and other tapioca cultivating parts of India.

Symptoms

Ø  CMD is characterized by the severe mosaic symptoms on leaves.

Ø  Light-green, yellow or white spots are formed on the leaves.

Ø  Affected leaves show mottling in the beginning.

Ø  Later the leaves show severe symptoms.

Ø  Discoloration, Malformation and Puckering of the leaf blade occur.

Ø  Vein clearing, vein banding and vein thickening.

Ø  The entire plant becomes stunted.

Ø  Diseased plants can be recognized even from long distance.

Causal Organism

Ø  Cassava mosaic disease is a viral disease

Ø  Caused by Cassava Mosaic Virus (CMV) (Tapioca Mosaic Virus)

Ø  CMV is a single stranded DNA virus of the Family Geminiviridae.

Ø  The virus is transmitted by an insect vector called Whitefly (Bemisia tabaci).

Etiology-Disease cycle (Spread of disease)

Ø  The CMD disease is spread and transmitted by the sap-feeding whitefly (Bemisia tabaci).

Ø  Bemisia tabaci act as the vector for the spread of the disease.

Ø  Vector: an agent which act as the carrier of the pathogen.

Ø  Other causes of transmission:

$  Vegetative propagation (use of cuttings from infected plants)

$  Mechanical transmission through sap, seeds of pollen grains.

$  Biological transmission by fungi, nematodes and other insects.

Control measures

Ø  Since CMD is a viral disease, no treatment to recover the affected individuals.

Ø  Controlling the insect vector is the best option to prevent the spread of the disease.

Ø  Sanitation practices such as removing and burning the infected plants is effective.

Ø  The proper use of cultural instruments

Ø  Changing the planting season is also effective.

Ø  Tapioca planted after the beginning of the rainy season is less susceptible to disease.

Ø  Use of resistant varieties such as S-1310, S-2380 and H-97

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