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Impact of climate change on sugarcane diseases

Sugarcane family Gramineae (Poaceae) is widely grown crop in Pakistan. Sugarcane originated in New Guinea where it has been known for thousands of years. Sugarcane plants spread along human migration routes to Asia and the Indian subcontinent. Agriculture is central to economic growth and development in Pakistan. Being the dominant sector it contributes 21.4 percent to GDP, employs 45 percent of the country. Sugarcane is a cash crop along with source of white crystal sugar. It also provides grower with a very good substitute of sugar as ‘gur’ and ‘khandsari’ (brown sugar). Sugarcane tops serve as fodder for cattle, baggage and leaf trashes as fuel, stubble and roots as organic manure and crop residues as mulch and compost
There are many obstacles, including heavy losses, caused by a number of diseases to the sugarcane crop in Pakistan. More than 50 diseases are reported in sugarcane, fungi, bacteria, viruses and nematodes cause the most destructive diseases and all these factors depend on the environmental changes
Sugarcane is a tropical crop. It requires warm and humid climate for growth while cool, sunny and dry climate for ripening. The temperature requirement is 20 0 C to 26 0 C. Germination does not take place when temperature goes below 7 0 C. Both the extremes of temperature is harmful. Severe cold arrests the growth, while attack of stem borer increases in hot weather. It requires more than 1,375 mm annual rainfall when grown as rain fed crop.. Rainfall deficiency produces a fibrous cane, whereas too heavy rainfall reduces sugar content.
Different diseases of sugarcane in Pakistan which influence the yield loses
1)    STEM CANKER (Cytospora sacchari)
Symptoms: The disease causes wilting of canes. The affected canes show drying of leaves from top to bottom. The cane stems are shriveled with considerable reduction in quantity and quality of juice. Small black dot-like bodies of disease causing fungus may develop on bud sheaths and hollow portions of canes. Sometimes only a few internodes are affected, but whole stool or only a few canes in a stool may also be affected. Perpetuation: The fungus remains in diseased canes or plant debris, which remains lying in the fields after the harvest of crop. Raton crop also helps the disease causing fungus to survive.
WHIP SMUT (Ustilago scitaminea)
Symptoms: The affected canes produce long, black whip-like and coiled or curved shoots, which are covered with a thin silvery membrane, containing masses of chlamydospores of the fungus. The smutted shoots may arise from the top of the cane or from lateral buds.
Perpetuation: The disease is carried over from year to year by ratooning or planting sets taken from smutted shoots of cane. Soil borne infection may also takes place, while wind disseminates disease. Control: Following measures are suggested for prevention as well as control of the disease: Sets from smutted canes should not be used for planting. Seed-sets should be disinfected either in 0.1 per cent mercuric chloride or formaline solution for 5 minutes followed by 2 hours covering under a moist cloth. The other effective chemicals available in market may also be used. Hot water treatment of sets at 52OC for 18 minutes can help eliminate the internal infection. Smutted plants should be rouged out and burnt before the bursting of the spores. Ratooning of the diseases crop should be discoursed. Suitable rotations with non-host crops should be practiced. Planting should be done in healthy soil. Dry sowing of the crop should be carried out, where disease is prevalent. Autumn planting of sugarcane should be avoided. Use of resistant varieties should be encouraged.
2)    Red Rot (Colletotrichum falcatum)
Symptoms: The disease first appears as red bright lesions on mid rib of leaves and shows itself as drooping and changing of colour of upper leaves. Withering of the leaves proceed downward. Usually third or the fourth leaf from the top is affected and shows drying at the tip. The pith becomes red and later on brown. In severe cases complete destruction of the stools is brought about. When the infected canes are spilt open they gave out an alcoholic smell due to fermentation and show-reddened areas.
Perpetuation: The disease is perpetuated from year to year by planting sets from infected canes and also through the fungus that remains viable on diseased canes lying in the field or ratooning of the crop. Control:  Ratooning should be avoided Uses of resistant varieties are recommended.
3)    Leaf spot (Helminthosporium spp.)
Symptoms: The disease may be characterized itself on leaves as small lesions, which gradually enlarge along mid rib and assure dark red to brown colour. In severe infection, the leaves become dry affecting photosynthesis. Perpetuation: The disease perpetuates through the fungus present in the affected leaves lying in the field and spreads fresh crop of conidia falling on leaves of adjacent plants. Control: Collection and burning of leaves or phyto-sanitary precautions in suppressing the source of inoculum reduces the incidence of disease. Disease-free sets of eight-month-old sugarcane nursery may be preferred for planting Mostly weeds serve as alternate hosts or sources of infection for pathogenic diseases Ratooning of the diseased crop should be discouraged.
The writers are associated with the Department of Plant Pathology, University of Agriculture Faisalabad, Pakistan. They can be reached at <zeeshansattar2206@yahoo.com>
 


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