Molecular Plant Pathology - Pathogen Profiles
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Cotton leaf curl disease, a multicomponent begomovirus
complex
Rob W. Briddon
Department of Disease and Stress Biology, John Innes Centre, Colney Lane,
Norwich, NR4 7UH, UK
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| Summary: |
Cotton leaf curl is a serious
disease of cotton and several other malvaceous plant species that is
transmitted by the whitefly Bemisia tabaci. The disease is, at this
time, endemic throughout Pakistan and epidemic in Western India. Affected
cotton plants exhibit a range of symptoms such as leaf curling, stunted
growth and a poor yield of cotton fibre. In addition, affected plants may
develop leaf-like outgrowths from the veins on the undersides of leaves. A
number of distinct begomoviruses have been shown to be associated with
infected plants, all of which require a satellite component (DNA ß) to
induce symptoms in cotton. DNA ßcomponents are a group of recently
identified, symptom modulating, single-stranded satellite molecules. An
additional, satellite-like component, DNA 1, is invariably found in
diseased plants, although it is not required for disease development. |
| Taxonomy: |
The viruses associated with the
CLCuD complex on the Indian subcontinent, five of which have been
identified thus far, are all single component begomoviruses (genus Begomovirus
family Geminiviridae). The satellite (DNA ß) and satellite-like
(DNA 1) components have yet to be classified, although the DNA 1
components are closely related to, and thought to have originated from,
components of a second group of single-stranded DNA viruses, the
nanoviruses (family Nanoviridae). |
| Physical properties: |
The begomoviruses associated with
CLCuD, like all geminiviruses, have geminate (twinned) particles,
approximately 18-20 nm in diameter and 30 nm long, consisting of two
incomplete T = 1 icosahedra joined together in a structure with 22
pentameric capsomers and 110 identical protein subunits. It is probable,
although not conclusively proven, that the DNA 1 and DNAß components,
being half the size of the viral component, are encapsidated in monomeric,
rather than geminate particles. |
| Disease symptoms: |
Symptoms in cotton usually appear
within 2-3 weeks of inoculation by B. tabaci and are initially
characterized by a deep downward cupping of the youngest leaves. This is
followed by either upward or downward curling of the leaf margins,
swelling and darkening of the veins as well as the formation of enations
on the veins, which frequently (dependant on variety) develop into
cup-shaped, leaf-like structures |
| Disease control: |
Control of CLCuD is mainly based on
insecticide treatments against the insect vector (Bemisia tabaci).
Roguing, the removal of affected plants, particularly of ratoon cotton
from the previous seasons crop, is recommended but appears to have little
affect in reducing the incidence of the disease. More recently, resistant
cotton cultivars have been introduced that were developed by conventional
breeding/selection. After initially showing promise in the control of
CLCuD, recent reports have suggested that the virus complex has overcome
the resistance. |
| Useful websites: |
http://www.danforthcentre.org/iltab/geminiviridae/
http://gemini.biosci.arizona.edu/ |
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This photograph was taken in a field in Haryana
state, India, in 2001
showing the typical foliar symptoms of CLCuD.
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