Cotton Leaf Curl Disease
History of Cotton leaf
curl disease:
Cotton leaf curl disease was first observed from
Nigeria in 1912 and a second epidemic of this disease in Nigeria was reported
in 1924. The main specie of cotton cultivated in Egypt and Sudan is
G.barbadense. The disease was also reported from Tanzania, Sudan in 1926 and
1934. Cotton leaf curl disease was observed as the most harmful
disease of cotton and it causes great economic losses. In Pakistan, the disease
was observed in 1967. The disease-resistant varieties of cotton helped to overcome
the losses, the disease was again observed due to new recombinant strain.
Etiology of Cotton leaf
curl disease:
Begomovirus
complex is a causative agent for Cotton leaf curl disease. This
complex consisting satellite molecule and begomovirus, this satellite molecule
belongs to a recently recognized group known as DNA β. The third single-stranded
component named as DNA 1 was also observed in all plants that were infected
with Cotton
leaf curl disease.
Transmission of Cotton
leaf curl disease:
The
whitefly, Bemisica tabaci act as
vectors that feed Begomovirus causing cotton leaf curl disease and
transmit it to other non-diseased cotton plants producing disease in them within the next six hours. There is no mechanical source other than whitefly to
transmit this disease. It is not spread through seed or soils either. There are
other alternative hosts through which the whitefly captures the virus and
creates the site for primary infection on the cotton plant. These hosts may be an
eggplant, Abelmoschus esculentus or Hibiscus rosa-sinencis. The insect-like
whitefly takes this begomovirus from the site of primary infection and transmits it
to other plants causing secondary infection in them. The whitefly, under suited
environment, can produce a massive population of viruses in greenhouses as well
as in field areas. There would be different capabilities shown by a peculiar
population of viruses to transmit begomovirus within particular hosts.
Begomovirus associated with Cotton leaf curl disease:
The
begomovirus belong to the family geminiviridae are the plant infecting virus
which infects the plants in a wide range. Multan strain of Cotton leaf curl disease
has been infected by six begomovirus species.
Types of begomovirus
species caused Cotton leaf curl disease:
These different six species are CLCuKoV (Cotton leaf curl Khokhran virus), PaLCuV (Papaya leaf curl virus), ToLCKV (Tomato leaf curl Karnataka virus), CLCuAV (Cotton leaf curl Alabad virus) and cotton leaf curl Rajastan virus. Cotton plants are most affected by the attack of more than one virus.A begomovirus cotton leaf curl Gezira has been identified which is different from southern Indian begomovirus species. Cotton leaf curl Bangalore virus which is isolated from Cotton leaf curl disease and causing severe disease symptoms in northern India. But in northern Africa, a virus is Gemini viruses that are closely related to other viruses in an area of different crops. Burewala strain of Cotton leaf curl disease is a recombinant virus combination of two virus sequences, cotton leaf curl Multan virus and Cotton leaf curl Kokhran virus, and showing resistance factors in cotton.
DNA 1 associated with
cotton leaf curl disease:
Virus isolated from Cotton leaf curl disease DNA 1 which is identified as satellite-like molecule has the ability of autonomous replication in the cells of the host plants. These cells are smaller in size than begomoviruses approximately (1375 nucleotides). They have a single gene that encodes the rolling circle replication initiator protein. Begomoviruses used for systemic movement in insects and plant transmission between plants and required by the monopartite DNA β. After begomoviruses, nanoparticles are single-stranded plant infecting viruses which represent as second family is closely related to DNA 1 components. Nanoparticles have several components (6 to 8) and pass from one plant to another through aphid in a circulative way. DNA-R is the components of nanovirus which replicates all the bona fide viruses. The majority of nano viruses are inspected as parasites are linked with Rep encoding components. Geminivirus either used for movement or encapsidation while DNA 1 components are more favorably used for encapsidation in monomeric capsid because of sequence rich in adenine.
DNA β associated with
cotton leaf curl disease:
The
DNA β molecules also associated with begomovirus has conserved structure with
200 nucleotides region of sequence rich in adenine and region of sequence with
100 nucleotides in length. Since 2000, full-length DNA β sequences have
been put down with the database. DNA β molecule performed the function by using the
product of βC1 gene in nicotiana
benthamiana. It causes the
pathogenic symptoms like swollen vein and occasional enations due to the
constitutive expression of Cotton leaf curl disease βC1.
Cotton leaf curl disease
with βC1 gene:
Gene
βC1 caused symptoms like outgrowth, vein darkening, and swelling with the
expression of potato virus X vector in both N.
tabacum and N. benthamiana which
differentiate from Cotton leaf curl disease. Furthermore, RNA interference, binding
with DNA, and movement of the virus from one plant to another was the functions
performed by βC1 gene.
Cotton leaf curl disease
DNA β:
The
A- rich conserved structures used to enlarge the component of half begomovirus
size and movements by the begomovirus are the important characteristics of Cottonleaf curl disease DNA β components. The SCR predicts the structure which
contains the approximately 80 nucleotides sequence of all β DNA components.
It represents the hairpin structure which comprises the loop sequence TAATATTAC
are less conserved that interspaced with the conserved sequence of the upstream region.
The loop sequence for geminiviruses and nano viruses originated from the virion
part of DNA replication. The distinct begomoviruses are captured by Cotton
leaf curl disease DNA β because the Multan strain of Cotton
leaf curl disease is linked with only DNA β. Due to this finding, their
symptoms vary in plant age infected by virus and cotton variety.
