SCALD DISEASE a -' =a.i

OF SUGARCANE

Sugarcane Breeding Institute Indian Council of Agricultural Research

Coimbatore - 641 007 TCAR

LEAF SCALD DISEASE OF SUGARCP "I

The disease caused by the bacterium Xanthomonas albilineans (Ashby) Dowson is one of the important diseases of sugarcane. The disease occurs in most of the sugarcane growing countries in the world. In India, the disease occurs in sporadic to epidemic form in subtropical India and in coastal regions of Andhra Pradesh and Tamil Nadu. The disease severity differs from place to place depending on the varieties and prevailing climaticconditions.

The disease manifests in two forms viz. chronic phase and acute phase. The chronic phase is expressed by several external symptoms. The most typical symptom of the disease is

, the presence of about 1-2 mm wide 'white pencil line' stripes or blights parallel to mid ribs and extending to leaf sheath (Fig. 1). Later the blights broaden and diffuse, resulting in the drying of leaf lamina which leads to withering of leaves. The drying is always from tip downwards, giving a scalded appearance to the clump. Leaf scald can also cause a partial or complete chlorosis of the leaf. Another important external symptom is sprouting of lateral buds in acropetal manner (Fig. 2). This is different from side shooting which occurs from flowering or damage to the apex, in that the side sprouts at the base of stalks may be more developed than those higher up. But in this case,

I the side sprouts usually show characteristic white to creamy

Fig -1. LSD infected canes showing Fig -2. LSD infected plants showing longitudinal leaf blights extensive leaf drying with bud sprouting

stripes, like the one produced on the main shoot. In due course these sprouts also die. In additioh to the external symptoms, diseased stalks also exhibit prominent internal symptoms of bright to dark red streaks due to necrosis of the vascular bundles (Fig. 3). These streaks are usually more prominent at the nodes, but may be present in the internodes, and are invariably present in side shoots and help to distinguish them from those caused by other diseases. Longitudinal lysigenous cavities may also develop inside the badly affected stalks, in ' nodal and internodal areas, particularly near the shoot apex. These cavities may also contain some bacterial slime or gum substance. When pieces of diseased leaf having whitish stripes are examined under microscope, characteristic bacterial ooze is observed.

The acute phase is characterized by a sudden wilting and death of mature stalks, often without previous symptom expression. The onset of this condition generally follows a period of stress, especially prolonged d r - weather or dry weather f rainy period. ,;. .! . - . . .C

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The chronic phase is mostfrequentlyobierved in young shoots emerging from infected setts or shortlyafter ratooning. In these situations someofthe affected shoots die and some continue to exhibit symptoms throughout the life of the plant. In some of the affected shoots disease may disappear and grow normally. However such shoots carry the inoculum in latency and the disease may beexpressed during maturity phaseor in ratoons.

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Fig -3. LSD infected canes showing Fig -4. LSV patnogen ~solated from vascular discolouration at nodal infected sugarcane on a

and internodal tissues special medium

.- - . . Wilbrink's agar is the selective me

I pathogen. The associated bacterium can be readily isolated

[ from all the infected parts of sugarcane plant but the bacteria

I are most frequently isolated from pencil-line leaf blights. The - bacterial colonies are circular, convex, smooth, shining,

. translucent, non-mucoid and produce a honey-yellow pigment which imparts a darkercolouration upon ageing (Fig.4).

Leaf scald is transmitted mainly by infected cuttings and mechanically by implernents/tools used for cane planting, . '

. Aerial transmission ofX. albilineans has been reported in some; , I.. countries. The disease is favoured by strong precipitatioq ,

during cyclonic periods.

Use of resistant varieties is the most effective means of controi and therefore, susceptible cultivars should be eliminated from -

I cultivation. In areas where the disease is sporadic, seed canes- should be obtained from disease-free nurseries. Further, - prophylactic measures are also required to control the disease, .

especially destruction of volunteer sugarcane shoots from diseased stools, disinfection of cutting tools by soaking in:, bactericides and control of grass weeds.

Extension ~ u b l i c a t i o n ' ~ ~ . 122 (2007)

Script by : Dr. R.Viswanathan Dr. M. Balamurali krishnan and Dr. P. Malathi

Prepared by : Dr. R.Thiagaragan Dr. Rajula Chandran and Dr. D. Puthira Prathap

Published by : Dr. N. Vijayan Nair, Director, Sugarcane Breeding Institute Coimbatore 641 007

Printed by : Print-Rite, Coimbatore