The Cotton Leaf Curl Disease in the Indian Subcontinent

Geographical Distribution

The leaf curl disease of cotton (Gossypium hirsutum L.) was first observed in Multan, Pakistan, in 1967. The disease reappeared in 1987 in its epidemic form in most of the cotton-growing areas of Pakistan. In 1992, the disease was observed throughout the central and southern parts of Punjab in Pakistan. During 1997-98, the disease was established in the border areas of India (Rajasthan, Haryana, and Punjab), joining the southern Punjab of Pakistan. The most devastating virus known as cotton leaf curl Multan virus (CLCuMV) is attributed to huge losses throughout the Indian subcontinent. The estimated direction ofmovement for the disease is from the center of Pakistan to northern and southern districts of India. Nowadays, the disease can be observed in all primary or secondary cotton-growing areas of the Indian subcontinent (Figure 5).

Symptoms and Losses

Cotton leaf curl disease (CLCuD) is not a seed-borne disease, but is only transmitted through whiteflies. After 2-3 weeks of virus inoculation by the insects, vein thickening on young leaves can be observed. Later, upward or downward curling of leaves starts and a cup-shaped leaf enation appears at the underside of the leave (Figure 6). The infected plants remain stunted throughout their life cycle and may lose 100% of the total yield. Disease spread can be observed with the wind direction. During the last two decades, the disease caused heavy cotton yield losses which reached up to US$ 5 billion in Pakistan in 1992-97. Recently, the introduction of relatively resistant varieties has selected a more aggressive virus in 2002 in central Pakistan, called cotton leaf curl Burawalia virus (CLCu-BuV), and this strain is now prevailing in all cotton-growing areas of Pakistan.

Causal Agent and Classification of Cotton Leaf Curl Disease

The begomoviruses associated with CLCuD are mono-partite begomoviruses with an associated ssDNA satellite molecule known as DNA-p (beta satellite).

According to sequence analysis of the available sequences in gene bank, there are viruses belonging to seven different species involved in the etiology of CLCuD named as, CLCuMV, cotton leaf curl Kokhran virus (CLCuKV), cotton leaf curl Rajasthan virus (CLCuRV), cotton leaf curl Allahabad virus (CLCuAV), cotton leaf curl Burawalia virus (CLCuBuV), cotton leaf curl Bangalore virus (CLCuBV), and papaya leaf curl virus (PaLCuV). Cotton leaf curl Bangalore virus is only present in the Bangalore district of southern India, while viruses belonging to the other six species are widespread throughout the cotton-growing areas of the north of the Indian subcontinent.

The area of maximum diversity for CLCuD is in central parts of Pakistan, hosting viruses belonging to five species of cotton leaf curl viruses (CLCuVs) and one of PaLCuV.

CLCuD is in reality caused by a complex of viruses associated with virus satellites. A monopartite gemini-virus, belonging to different species of viruses, is typically associated with a beta satellite (DNA-p) or a DNA-1 satellite. If DNA-p's have only been found associated with geminiviruses, DNA-1 satellites have originally been found associated to nanoviruses. Both satellite genomes are encapsidated by the geminivirus capsid protein, and thereby both are transmitted by whiteflies. Full-length clones of several CLCuVs DNA-A were unable to reproduce the symptoms in cotton and other different hosts such as tobacco. Infectious clones of DNA-1 were also not capable of inducing symptom development of CLCuVs in the inoculated plants.

With the discovery of DNA-p, it was proved that both DNA-A and DNA-p are necessary to induce typical symptoms of CLCuD, while DNA-1 is not necessary to induce the symptoms and is seldom found in association with the disease complex. At present, the origin of DNA-p is unknown but it can be transreplicated by diverse geminiviruses associated with the CLCuD complex. The DNA-p is only ±1300 nt long and codes only for one ORF called pC1. The gene |bC1 codes for a strong suppressor of gene silencing, thereby providing a tremendous advantage to the cognate helper virus. DNA-1 satellite codes for a Rep protein that allows this satellite to be replicated on its own, but the satellite depends on the helper virus for all the other functions, such as gene-silencing suppression, movement, and transmission. DNA-p is dependent on DNA-A for replication, movement, and transmission. The genome organization of DNA-A is typical of any other begomovirus and has no similarity with its associated satellite molecules. Both DNA-p and DNA-1 are approximately half the size of DNA-A, that is, 1350 nt.

Epidemiology

Cultivated cotton or upland cotton (G. hirsutum) was introduced into the Indian subcontinent from southern

Line of Control

AFGHANISTAN

NORTH WEST FRONTIER PROVI

Line of Control

AFGHANISTAN

NORTH WEST FRONTIER PROVI

Leaf Curl Disease Cotton

Figure 5 Localization of cotton leaf curl geminiviruses in the Indian subcontinent. PaLCuV, papaya leaf curl virus; CLCuMV, cotton leaf curl Multan virus; CLCuRV, cotton leaf curl Rajasthan virus; CLCuKV, cotton leaf curl Kokhran virus; CLCuAV, cotton leaf curl Allahabad virus; CLCuBuV, cotton leaf curl Burawalia virus; CLCuBV, cotton leaf curl Bangalore virus.

Figure 5 Localization of cotton leaf curl geminiviruses in the Indian subcontinent. PaLCuV, papaya leaf curl virus; CLCuMV, cotton leaf curl Multan virus; CLCuRV, cotton leaf curl Rajasthan virus; CLCuKV, cotton leaf curl Kokhran virus; CLCuAV, cotton leaf curl Allahabad virus; CLCuBuV, cotton leaf curl Burawalia virus; CLCuBV, cotton leaf curl Bangalore virus.

Mexico during the nineteenth century. In its native place, cotton is not associated with virus diseases as in the Indian subcontinent. CLCuD complex most probably evolved from some wild species of cotton growing over a long period of time or from other weed hosts present before the cultivation of upland cotton in this part of the world. In 1991, a new variety of cotton (S12) was introduced from

Texas, because of its excellent fiber qualities; unfortunately, this new variety was hypersensitive to CLCuD and the disease propagated very quickly after this introduction. The CLCuD threat was greatly increased due to intensive cotton cultivation, monocropping pattern of agriculture, and overlapping seasons of other crop plants. CLCuVs can infect a number of diverse hosts in the

Downward Leaf Roll
Figure 6 Downward leaf curl symptoms of cotton induced by the CLCuMV in association with the cotton leaf curl Multan beta satellite.

families Malvaceae and Solanaceae. The virus infection was not highly noticed at the early beginning of the epidemic, when perhaps it could have been possible to eradicate the disease. The disease is transmitted through whitefly in a persistent manner. The disease spread is directly correlated with the spread of the whitefly population, along the prevailing wind direction.

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  • kaisa
    What is CLCuD complex?
    6 years ago

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