GRASSY SHOOT DISEASE O F SUGARCANE
Indian Council of Agricultural Research Coimbatore - 641 (407
GRASSY SHOOT DISEASE OF SUGARCANE
1I * 1 1
The grassy shoot disease (GSD) of sugarcane occurs in most of the Asian countries, affecting sugarcane production to a considerable level. The disease is caused by grassy shoot phytoplasmas. In India the disease occurs in all the sugarcane arowing states. -
The disease symptoms are readily seen in germinating shoots. However it is difficult to differentiate from the deficiency related. symptoms since in both cases production of chlorotic tillers are' seen. However the GSD symptoms will be very clear by two months with chlorotic or partially chlorotic leaves in the whorl and green leaves in the base (Fig.1). Later production of lean, lanky, chlorotic or green tillers in numerous numbers will be observed (Fig.2). In addition to stunting, in many instances the affected canes exhibit premature proliferation of axillary buds (Fig.3). One or two thin, weak and small millable canes are produced in a clump having primary infection and these canes do not produce arrows. The buds of such canes are usually papery and abnormally elongated. In some cases, there is also formation of aerial roots at the lower nodes. The root system of the affected plant is considerably reduced towards the fag end of crop growth.
The disease displays different types of symptoms at different growth stages. However the patent symptom is profuse tillerring. In such tillers, either partial or complete chlorosis is
FM 1, Gmwy shoot infected sugarcane showing chlotutii leaves in the top with chlorotic tillers
FIG 3. GSD infected canes showing bud sprouting with axillary tillers
observed. Rarely production of numerous tillers without Fig -2. chlorotic leaves is also observed. In ratoon crop, initiation of shoots is delayed in GSD affected stools. Production of thin chlorotic shoots may be produced in the ratoons but such tillers die in a few weeks. The disease is very common in fields of neglect and where multiple ratoons are practiced. Also when cane-farming is practiced with own seed for many years the disease attains the severe form. In severe cases, the affected fields show no millable canes, the clumps will be bushy with dried grassy shoots and few partially chlorotic leaves emerge from such bushes.
Phytoplasmas are the causative agent of the disease. These are single cellularorganism with only unit membrane. They lack rigid cell wall. This group of pathogens usually colonizes sieve tube elements in phloem systemically, there by blocking the movement of photosynthates from leaf to stalk and root. This results in poor growth of sugarcane and reduced sugar recovery. Also the altered metabolism in the host induced by the pathogen infection causes different types of symptoms such as albino, excess tillering, leathery leaves, bud sprouting etc.
The disease is primarily transmitted through infected setts and secondary transmission takes place through insect vectors.
weass tiller production in GSD affected sugarcane, ~r#ga~ha Lmft IMed clumps with mostly green tillers
Rght - Infected clump with mostly chlorotic tillers
Usually in plant crop the symptoms appear in the field depending upon the phytoplasma titre available in the planted setts. In case of low titre, the expression is delayed or it is expressed only in ratoons. Ratoon crop always shows h expression of the disease which is due to build up of inoculum from plant crop to subsequent ratoons.
As vegetative propagation in sugarcane favours harbouring of different pathogens including grassy shoot phytoplasmas adequate care should be taken while selecting seed canes.Any crop with 2% GSD incidence is unsuitableforseed purpose.
Seed cane plots are to be monitored periodically forthe disease .at regular intervals. Always seed canes should be selected from such carefully monitored fields. Tissue culture seedlings derived through meristem ensures freedom from the pathogen. However it is advised to select a mother plant (for meristem culture)from well maintained fields. Three-tier seed production system is a viable procedure to maintain the area disease free and obtaining healthy seed.
If the disease free materials are not available, heat therapy (either aerated steam or moist-hot air) need to be employed to eliminate the phytoplasmal pathogen. Temperature regime of 50- 52째C for one hour is ideal to inactivate the pathogen. If the varieties are sensitive at 52"C, treatment time may be increased at 50째C for 2-3 hrs to inactivate the pathogen. During the course of heat treatment and further handling of the setts, a r e should be taken to minimize the loss to the buds. Always the heat-treated setts should be treated in fungicide solution to e settsfrom soil borne pathogens.