Ex. No. 15.           Study of Viral, Phytoplasmal & Viroid diseases

Virus:  Virus is a transmissible, sub cellular entity which replicates only in the living cell (biotroph) and consist of nucleic acid which is typically surrounded by a protein coat.  Ex. Tobacco Mosaic Virus

Dwarfism or Stunted growth is a common symptom produced by a virus.

Vector: Insects which transmit viruses are called as vectors                    

Disease name	Causal Organism	Symptoms	Vector
Tobacco Mosaic	Tobacco Mosaic virus (TMV)	Stunted growth, Alternate green and yellow patches are appear	Sap transmission
Bhendi yellow vein mosaic or Bhendi Yellow vein clearing	Bhendi Yellow Vein Mosaic Virus (BYVMV)	Veinal Chlorosis	White fly –                     Bemisia tabaci
Tomato Spotted Wilt	Tomato Spotted Wilt Virus (TSWV)	Bronzing of veins, Leaves are reduced in size. Concentric rings and Mosaic mottling on fruits.	Thrips –                     Scirtothrips dorsalis
Chilli leaf curl	Tobacco Leaf Curl Virus (TLCV)	Curling of leaves like a boat or spoon structures	White fly - Bemisia tabaci
Chilli mosaic	Chilli mosaic virus	Stunted growth, Alternate green and yellow patches are appear. Mottling and Puckering of leaves	Aphids – Aphis gossypii
Banana Bunchy top	Banana Bunchy Top Virus (BBTV)	Bunchy appearance of leaves. Leaves are reduced in size and become chlorotic. They are brittle and the infected plants do not grow more than 3 feet.	Black aphid –              Pentalonia nigronervosa
Black gram leaf crinkle	Urdbean Leaf Crinkle Virus (ULCV)	Crinkling and Curling of leaves.	White fly –                     Bemisia tabaci & Aphid
Cassava Mosaic	Indian Cassava Mosaic Virus (ICMV)	Stunted growth, Alternate green and yellow patches are appear. Tuber splitting symptoms are appear.	White fly –                      Bemisia tabaci
Rice Tungro	Rice Tungro Virus (RTBV – Rice Tungro Bacilliform Virus & RTSV– Rice Tungro Spherical form Virus)	Orange yellow colour discolouration from the tips of lower leaves (Tungro – Degenerated growth)	Green Leaf Hopper – Nephotettix virescens
Pulses Mosaic	Cowpea Aphid Borne Mosaic Virus	Stunted growth, Alternate green and yellow patches are appear.	Aphid - Aphis gossypii

Phytoplasma : Mycoplasma Like Organisms (MLO) which are infect the plants called as phytoplasma. They are lack of cell wall, gram negative and sensitive to Tetracycline (Mollicutes group). 

Disease name	Causal Organism	Symptoms	Vector
Little leaf of Brinjal	Candidatus Phytoplasma	Small, narrow pale green colour leaves. Shortening of internodes with bushy appearance	Leaf hopper – Hishimonas phycitis
Sesame phyllody / Green flowering	Candidatus Phytoplasma	The flowers are transformed into green leaf like structure	Leaf hopper –           Orosius albicinctus

Viroid: Nucleic acid without protein coat. Viroids are transmitted through mechanical transmission.

Ex. Potato Spindle Tuber Viroid (PSTVd)

Smallest Viroid : Coconut Cadang Cadang Viroid