Ratoon stunting disease(RSD) in sugarcane is caused by a Rickettsia-like organism called Clavibacter xyli sub sp. xyli. The disease is characterized by stunted growth, reduced tillering, thin stalks with shortened internodes, yellowish foliage, and orange-red vascular bundles in shades of yellow at the nodes of infected canes. The pathogen is present in the xylem cells of infected plants. It can be spread through diseased setts or contaminated harvesting implements. Maize, sorghum, Sudan grass, and Cynodon are collateral hosts for the pathogen.
It is important to select setts from disease-free fields or commercial nurseries to manage ratoon stunting disease. Clumps showing disease incidence should be removed and burned. Setts should be treated before planting, as specified for grassy shoot disease. Chemical, biological, natural, and organic control methods may also manage the disease. Using resistant cultivars and crop rotation can also effectively reduce the incidence of ratoon stunting disease.
Ratoon Stunting Management in Sugarcane
The Causal Organisms of Ratoon Stunting Disease
Clavibacter xyli subsp. xyli, a Rickettsia-like bacterium, is the causative agent of ratoon stunting disease in sugarcane. The xylem cells of infected plants contain this pathogen. These small, thin, rod-shaped, or coryneform bacteria are Gram-positive. Collateral hosts like corn, sorghum, Sudan grass, and Cynodon can be infected and become a new source of infection.
The Disease Cycle of Ratoon Stunting Disease
Ratoon Stunting Disease is primarily transmitted through defective setts or contaminated harvesting tools. Leifsonia xyli subsp. xyli is present in the xylem cells of infected plants and can also infect secondary organisms. Crop rotation, the use of resistant cultivars, and integrated disease management strategies are effective at reducing disease incidence.
Causes/ Conditions Favorable for Ratoon Stunting Disease in the Field
Several conditions in the field promote the spread of Ratoon Stunting Disease, including infected plant debris and soil and using diseased setts or contaminated harvesting tools. The bacterium can persist in plant debris or soil for several months and only enters plants through wounds. It is readily transmitted mechanically via injury during planting, harvesting, and other agricultural activities.
Symptoms of Ratoon Stunting Disease
- Stunted growth, especially in stubble and ratoon crops
- Reduced tillering
- Thin stalks with shortened internodes
- Yellowish foliage
- Orange-red vascular bundles in shades of yellow at the nodes
- Pinhead-like orange-colored dots of bacteria on the internal soft tissue in the nodal region
- Poor germination of setts taken from diseased plants
- The slow growth of emerging shoots The disease is caused by a virus that infects many hosts falling under Graminae.
- It is sap-transmissible, and no insect vector has been found.