RATOON STUNTING OF SUGARCANE
Coimbatore - 641 007
RATOON STUNTING OF SUGARCANE Ratoon stunting disease (RSD) was first suspected as a physiological disorder in Australia and its spread worldwide as a bacterial disease was established later. The disease is caused by the xylem limiting bacterium Leifsonia (Clavibacter) xyli subsp. xyli(Daviset al.). The name RSD is a misnomer since the disease deleteriously retards the growth of plant crop aswell. DISEASE SYMPTOMS
Diseased clumps usually display stunted growth, reduced tillering, thin stalks with shortened internodes and yellowish foliage (Fig. 1). The characteristic stunting and unthriftiness associated with RSD are usually greater when the crop suffers from drought or waterlogging. The sugarcane varieties vary in their tolerance to the pathogen infection. Ratoon crops usually suffer more severely than plant crops. Diseased setts may germinate slowly and erratically, although there may not be any adverse effect on germinat~on.Growth of a diseased crop is slower than that of a healthy crop, and ultimately the yield is reduced. The reduction in yield is due to the production of thinner and shorter stalks rather than a reduction in the total number of canes (Fig.2). During drought conditions the total number of stalks may also be reduced and there is much irregularity In the length of individual stalks in a clump. In ratoons, growth initiation is slower than healthy plants. Stunting in the field is not uniform from clump to clump and diseased fields show a characteristic 'up and down' appearance, even if all plants are diseased. In general root mass is reduced in size, proportionally to the above ground parts, but the roots appearto be normal.
Diseased stalks of some varieties may exhibit an internal discolouration of vascular bundles at the lower portion of nodes, but these symptoms are often ephemeral. They appear as yellow to reddish brown dots, commas, or short lines when viewed by slicing longitudinally through nodes (Fig.3). The range of discolouration includes yellow, orange, pink, red and reddish brown and these colours usually stand out in marked contrast to the lightcoloured ground tissue of the node. The discolouration does not extend into the internode unlike similar symptoms due to other diseases. The colour of the affected vascular bundles varies in both shade and intensity with the degree of infection and with variety and it may vary within a single variety from time to t~me.The discoloured strands should be found right through the node, and all nodes in the fully developed part of the stalk
should show some symptoms. Severe RSD ,infection in Cauvery basin of Karnataka shows reddish brown or pale red discolouration of entire nodal region (Fig.4). Occasionally the discolouration extends to internodal . region along vascular bundles for few millimeters. In such canes severe stunting, internodal shortening and reduced cane thickness are observed (Fig.5). In general, such severely affected clumps show characteristic yellow leafdiseaseon the foliage.
The bacterium is unicellular and measures about 0.25-0.50 x 1-4 pm in size. The bacterium colonizes xylem vessels and remains in vessels and adjoining tracheids, parenchyma and lacunaeof thexylem. The bacterium can be isolatedfrom infected juice in a special medium, SC-medium.
The RSD bacterium is transmitted through disease infected setts. The disease spreads through knives while cutting the canes for seed purpose ordurinn harvestthrough implements. ment Cultivation of resistant varieties is the best option to manage the disease. If suitable resistant varieties are not available, the disease can be managed effectively by adopting an integrated approach.
Primary spread of the disease takes place through seed and this helps in disease introduction to new locationslfield. Hence going for healthy seed cane reduces chances of disease spread to the planting crop as well as in further ratoons. lection The bacterium is xylem-limited and occurs only in sugarcane in nature. However the pathogen can survive either in left over plant debris or in the soil and a break of at least six months is advised betweenplantings if the old crop was infected by thedisease.
Sanitation Sanitation is essential to prevent healthy cane from becoming infected since the RSD bacterium is easily transmitted mechanically, through cutting knives hence it is important to avoid contamination in them. Implements which are being used in diseased field should be cleaned of juice, plant debris, or dirt and then be decontaminated before entering healthy field. Disinfectants like Dettol (1%) may be sprayed onto the cutting surfaces, or the implements may be dipped or swabbed to eliminate the contaminating bacterium. Contact of disinfectants for 5 minutes ensures complete disinfection.
Heat therapy (hot water, hot air, moist air or aerated steam) is beneficial to reduce bacterial load in the seed cane. While treating canes by heat treatment, problem of reduced germination and lack of complete control may occur. To maintain germinability, the following steps are to be followed for the efficient functioning of the heat treatment unit during or after heat treatment, careful selection of canes, leaving leaf sheaths over the buds during treatment and immediate cooling of canesaftertreatment.
Factoryfarm should maintain RSD free nurseries developed through heat treatment or meristem culture derived plants. Wherever RSD is a problem following three-tier seed nursery programme is recommended to maintain disease free crops.
-n practices The disease is favoured by prolonged drought'or water logging. Hence adequate irrigation is required during summer months and also proper drainage during monsoon season to maintain optimum moisture status in thesoil. monitoring
To ensure that seed cane nurseries have minimal disease incidence and that sanitation practices are effective in preventing re-infection, nurseries and multiplication fields need to be monitored with simple diagnostic techniques likedot-blot or ELISA.
ExtensionPublication No. 120 (2007) Script by
: Dr. R. Viswanathan Dr. M. Balamurali Krishnanand Dr. P. Malathi
Preparedby : Dr. R.Thiagaragan Dr. Rajula Chandran and Dr. D. P uthira Prathap ublished by : Dr. N. Vijayan Nair, Director, Sugarcane Breeding Institute Coimbatore 641 007 Printed by
: Print-Rite, Coimbatore