COTTON is the most important cash crop the world over and for Pakistan it brings 64 per cent of total foreign exchange besides providing livelihood to a large population in rural urban areas. Cotton is vulnerable to a large number of diseases and insects.

The cotton diseases include root rot, cotton leaf mosaic, wilting of leaves, angular leaf spot or bacterial blight, boll rot, virticillium wilt and the most notorious, the leaf curl virus.

The root rot, as the name implies, is rotting of roots, is a very serious disease in Taxas (USA). A few patches of root rot have been noticed in cotton-growing areas with almost no economic impact. The casual organism remains alive for many years in the soil. Certain cotton varieties have relatively higher tolerance level. However, the writer, in some root rot patches adopted a number of measures at Bahawalpur and Bahawalnagar. The best control measure is still the very old recommendation of mix cropping of “moth” in cotton.

The reason for its suppression is yet unknown. The boll rotting cause some damage to bolls at the bottom of plant, owing to physical or mechanical injury because of high humidity. In some severe cases, losses may go up to 2 to 3 mounds of phutti per acre. It is more dominant in lower Sindh, where the humidity is considerably high. The best control measure is to cultivate narrow-leaved varieties such as okra and super okra (leaves like bhindi tori or ladyfinger).

The leaf mosaic is the appearance of discoloured spots on the leaves thus distorting the leaf shape. At the moment it is not of any economic significance, However in the past it appeared in some spots in Khanewal, Lodhran and Bahawalpur. Fortunately it disappeared in due course of time,— may be due to better management practices or inherent disease resistance.

As far as wilting of leaf is concerned it appeared on large scale in cotton fields in southern Punjab when leaves started exhibiting wilting signs late in the season when plants had already taken full load. Leaves started dropping or wilting despite fields being irrigated. This disorder appeared, both in small and large patches and was wide spread in the region.

The transpiration rate was higher as compared to moisture absorption by roots. Apparently, roots did not look damaged. The cause of disease remained unknown. The angular leaf spot or bacterial blight of cotton appeared on cotton crop in early 70s, which spread throughout cotton areas of Punjab. This was a soil-borne disease whose bacterium remained in debris or plant residue. The casual organism start invading the underside of leaf with splash of raindrops travelling upward on leaves with angular soaked leaf spots.

The intensity of spots increases on the leaves in rainy season in conjugation with high humidity. Thus the bacterium kills the protoplasm of leaves ultimately disrupting the process of photosynthesis. In case of severe incidence, the lesions appeared on stem and bolls.

The reduced photosynthesis led to less number of small bolls. It not only considerably reduced the yield with impaired quality. There were two ways to control the disease: one to bury the plant debris followed by deep irrigation to decompose bacterium and the other, of course, hybridization of new varieties by conferring B genes responsible for resistance. By the time, breeders’ initiated the process of developing new varieties, fortunately the disease vanished owing to better sanitary practices. By the time the bacterial blight faded, another deadly leaf curl virus was noticed in 80’s.

The cotton leaf curl virus symptoms are thickening of veins and appearance of small leaves on the lower side of the leaf called aenation. The plant height is considerably reduced affecting the number and boll-size and ultimately reducing the yield and the quality of the produce.

The cotton leaf curl virus belonged to the group of Gemini virus now has been named as ‘ Bgemo’ virus which thrives on many wild, cultivated and ornamental plants.The white fly mostly transmits the virus. Someextension workers advocated when you spot a white fly kill it by pesticide spray.Ultimately mismanagement led to white fly flare-up in the country.

So far we have utilized a limited sources of resistance except BH118, which could be dreadful any time. But I would suggest that we must study the genetic inheritance of disease resistance.

A time may come when virus mutate and the mutated virus becomes resistant to our stock, hence to safeguard the cotton future we must find out resistant genes from diversified source such as from desi cotton or Gossypium palmeri.

The cotton leaf curl virus, known throughout the world, also spread rapidly throughout Punjab. Wherever it spread, it totally devastated the crop. To overcome the virus it was suggested to suspend cotton sowing for five years. However it caused losses of billion of rupees and the future of crop was to be at stake. Had the cotton been suspended for five years, the country would have sustained losses valuing Rs2500 billion.

Realising the gravity of the situation, the then Chief Minister of Punjab, Mr Ghulam Hyder Vain, announced grant of two squares of fertile land to any expert finding its solution. Resistant varieties were evolved to overcome the virus without disrupting cotton cultivation. The writer is one of the breeders who bred resistant varieties. However the government of Punjab has yet to fulfil its commitment.