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Diseases of sugarcane

Causes, symptoms, transmission, poerpetuation and control.

By M MITHAL JISKANI,
Assistant Professor (Plant Pathology),
Sindh Agriculture University, Tandojam.

Oct 01 - 07, 2001

Sugarcane is not only cash crop for the growers, but it is main 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, baggase and leaf trashes as fuel, stubble and roots as organic manure and crop residues as mulch and compost (Bhatti and Soomro, 1996 and Khoso, 1992). It may also be kept in mind that sugarcane leaves are used as substrate for the artificial cultivation of edible mushrooms.

There are many constrains, including the heavy losses, caused by a number of diseases to the sugarcane crop in Pakistan. More than 50 diseases are reported in sugarcane, the most destructive diseases are caused by fungi, bacteria, viruses and nematodes. The losses (due to the diseases) vary from place to place, depending upon the crop variety. Overall, Table present area, production and yield per hectare of sugarcane crop in Pakistan. The causes of fluctuations in production may be many more, but the diseases could not be ignored, neglected and or regretted, because they also cause variable loss time by time to the crop. These all diseases are injurious in some areas, in some years and on some plant parts. All parts of plant are subject to disease and one or more diseases can occur on virtually every plant and in every field. All draw attention because of symptoms or signs and generate great concern because of their effects on the quality and/or quantity of cane.

Table: Area (000 hectares), production (000 tonnes) and yield (kg per hectare) of sugarcane in Pakistan

Year

Area

Production

Yield

1990-91

884

35,989

40,720

1991-92

896

30,865

43,371

1992-93

885

38,059

43,024

1993-94

963

44,427

46,144

1994-95

1,009

47,168

46,747

1995-96

963

45,230

44,968

1996-97

965

41,998

43,521

1997-98

1,056

53,104

50,288

1998-99

1,155

55,191

47,784

1999-2000P*

1,01

46,363

45,904

P=Provisional; *= Jul-Mar; Source: Economic survey 1999-2000; Govt. of Pakistan.

However, the causes, symptoms, transmission, perpetuation and control measures of different most important diseases of sugarcane, based on the description by Kamal and Moghal (1968), Hafiz (1986), Ahmad (1988), Bhatti and Soomro (1996), Bhatti and Jiskani (1996) and Jiskani (1999) are being summarized here under, for guide line to the growers, research and extension workers as well as students of agriculture.

WHIP SMUT (Ustilago scitaminea) Syd.

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. Later on that membrane rupture and release a multitude of spores, which contaminate soil and the standing crop. In certain cases, the infected plants remain stunted in growth with increased tittering of little value. The diseased plants are unfit for use.

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 take place, while wind disseminates disease.

Control: Following measures are suggested for prevention as well as control of the disease:

1) Sets from smutted canes should not be used for planting.
2) Seed-sets should be disinfected either in 0.1 % 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.
3) Hot water treatment of sets at 52oC for 18 minutes can help eliminate the internal infection .
4) Smutted plants should be rouged out and burnt before the bursting of the spores.
5) Ratooning of the diseases crop should be discoursed.
6) Suitable rotations with non host crops should be practised.
7) Planting should be done in healthy soil.
8) Dry sowing of the crop should be carried out, where disease is prevalent.
9) Autumn planting of sugar cane should be avoided.
10)Use of resistant varieties should be encouraged.

STEM CANKER (Cytospora sacchari) Butl.

Symptoms: The disease causes wilting of canes. The affected canes show drying of leaves from top to bottom. The cane stems are shrivelled 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 remain lying in the fields after the harvest of crop. Ratoon crop also helps the disease causing fungus to survive.

Control: The destruction of cane plant debris alone would control the disease in alkali soils. However, planting disease bee sets as well as the development and use of resistant varieties will be more practicable and economical control measure.

RED ROT (Colletotrichum falcatum) Went.

Symptoms: The disease first appears as red bright lesions on the mid rib of leaves and shows itself as drooping and changing of colour of upper leaves. Withering of the leaves proceeds downwards. 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 sever 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: Non ratooning and use of resistant varieties are recommended. Disinfecting of sets with effective and easily available chemicals.

LEAF SPOT (Helminthosporium spp.)

Symptoms: The disease may be characterised itself on leaves as small lesions, which gradually enlarge along the 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 sources of inoculum reduces the incidence of disease.

POKKAH BOENG (Fusarium moniliforme) Sheldon

Symptoms: Pokkah boeng meaning distorted top in Javanese. The disease appears in different stages representing development of chlorotic areas at the basal parts of the lower leaves, development of irregular reddish specks or stripes and appearance of top rot followed by total killing. The young leaves may also show pronounced wrinkling, twisting and shortening, depending upon the varieties and climatic conditions. In tolerant varieties there may be recovery of growth, when the conditions improve.

Perpetuation: Its causal agent was not established till 1927. It is now present in many countries, including Pakistan. However, it can not be asked that how the disease can survive.

Control: Do not use seed sets from diseased plants.

SUGARCANE MOSAIC VIRUS (SCMV, Potyvirus group)

Symptoms: Mottling of young crown leaves showing a definite pattern of alternating dark and light green coloured patches of varying size and run parallel to the midrib of leaf.

Transmission: Transmitted through mosaic infected sets and an aphid.
Alternate hosts
: Maize and sorghum.
Control
: Planting virus free sets and avoid ratooning of diseased crop.

MINOR DISEASES

The other minor diseases of sugarcane reported from Pakistan are: chlorotic streak virus, ratoon stunting, yellow spot, red stripe, rust and genetic variegation of leaf and sheath.