37. Impacts of Cotton Leaf Curl Virus on the Yield of Cotton In Pakistan

 Cotton Leaf Curl Virus

Cotton Introduction:

    Cotton is a type of natural fiber that grows in a protective case called a boll, around the seeds of plants belonging to the Gossypium genus in the Malvaceae family. The fiber is composed mainly of cellulose, with small amounts of waxes, fats, pectins, and water. In the wild, the cotton bolls help to spread the seeds.

    This versatile fiber is typically spun into yarn or thread and used to create textiles that are soft, breathable, and long-lasting.

History of CLCuV:

    Cotton leaf curl disease was initially discovered in Multan in 1967 and was not considered a significant threat until 1987. In 1988, however, the disease caused damage to the cotton crop on 60 hectares in the Multan district, leading to concerns about its potential impact. The following year, the disease affected 200 hectares, and by 1990, it had spread to 800 hectares. The situation worsened in 1991, when the disease appeared in epidemic proportions, affecting an area of 14,000 hectares in the Multan, Khanewal, and Vehari districts. 

        The disease continued to spread, with over 485,000 hectares affected in 1992, resulting in a decrease in production and significant financial losses for the country. In 1993, the disease spread throughout the entire Cotton Belt of Punjab, causing varying levels of damage on 889,000 hectares. The disease was also reported in D.G. Khan and Sindh.

Symptoms:

• The primary symptom of Cotton leaf curl disease is the thickening of the veins in affected plants. 
• Additionally, infected plants may display the yellowing of small veins on the underside of the leaves, as well as leaf curling. 
• In more severe cases, a cup-shaped leaf-like outgrowth may appear on the underside of curled leaves. 

• Early infection can lead to stunted plant growth and significant reductions in crop yield.

Spread or Transmission:

    The Cotton leaf curl disease is transmitted between plants through its carrier, the whitefly. This virus has the ability to thrive not only on cotton, but also on several other weeds and hosts, including ladyfingers (okra), eggplant, chilies, tomato, cucumber, tobacco, and melon during the off-season. The disease has the capacity to multiply on weeds and other hosts, as well as on plant debris from previous crops that are present during the season.

Control or Management:

• Planting multiple varieties of cotton.
• Growing tall varieties of cotton to minimize whitefly infestations.
• Clearing fields and the surrounding areas of weeds to reduce the availability of hosts for whiteflies and the virus.
• Regularly removing any CLCuV-infected plants to prevent the further spread of the disease.
• Applying nitrogen during sowing to promote initial plant growth.
• Ensuring adequate irrigation, especially during the hot months of May, June, and July, to prevent water stress and maintain growth rates.
• Irrigating each field separately to avoid the spread of the disease.
• Practicing crop rotation with non-host crops to reduce the buildup of the virus in the soil.
• After harvesting, plow all plant debris into the soil or burn them if possible.
• Apply a seed treatment with Imidacloprid 600 FS at a rate of 5 ml/kg and Thiamethoxam 250 g/kg at 25% w/w to effectively control the virus.
• To combat whitefly attacks (the vector of CLCV), use effective insecticides such as diafenthiuron 500 g/L at 47.2% w/w, imidacloprid 200SL at 250 ml/acre, or acetamiprid 20SP (e.g. Mospilan) at 125 gm/acre during May, June, and July to control the whitefly. Buprofezin has been proven effective against nymphs, while acetamiprid, diafenthiuron, and imidacloprid have been effective against whitefly adults.

Impacts of CLCuV on the Yield of Cotton:

• In 1991-92, the highest-ever production of cotton was achieved, with 12.8 million bales being produced. 
• However, in the following years, there was a downward trend in production, with only 8.04 million bales being produced in 1993-94 due to a severe outbreak of cotton leaf curl disease (CLCuV), which caused significant damage to the cotton crop. 
• Unfortunately, since then, a decline in yield due to CLCuV has been a regular occurrence every year, resulting in the loss of approximately 6.5 million bales over the last decade.
• Fortunately, due to an increase in the cultivation of relatively tolerant or resistant cotton cultivars, along with other remedial measures taken against CLCuV, the declining trend in cotton production has been checked and even reversed. 
• For example, in 1995-96, the country was able to produce 10.06 million bales of cotton. However, during 1996-97, production declined again to 9.35 million bales due to severe attacks from whitefly and leaf curl virus, as well as continuous hot and dry weather.
• With the increasing prevalence of CLCV in Punjab and its transmission by the whitefly (Bemisia tabaci), a monitoring program was launched in Sindh in 1996, with a focus on geminiviruses including CLCV. The disease was first detected near Ubavro, an area close to the Punjab-Sindh border. 
• Since then, the incidence of CLCV has been on the rise, spreading from Ubavro to other areas. The disease has now traveled as far as Sakrand, which is located about 450 kilometers away from the original site of its detection in Ubavro. 
• The spread of the disease over the past three years has been a cause of concern for farmers and agricultural authorities in the region.

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