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.
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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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