Law on control of sugarcane ratoon dwarfing disease

Ratoon Stunting Disease (RSD) was first reported in Taiwan, China, in 1954. Since then, Guangdong and Fujian provinces in mainland China have also experienced outbreaks of the disease. So far, no reports have been made from other sugarcane-growing regions. The disease is more severe in arid areas, where it causes significant economic losses. The pathogen responsible for RSD is *Clavibacter xyli* subsp. *xyli*, a coryneform bacterium. This microorganism resides within the vascular tissues of infected sugarcane plants. It has a distinctive morphology: the bacteria are straight or slightly curved, slender, thin-walled, and sometimes show one end swollen. They do not swim and are Gram-positive. The distribution of the bacteria within the plant is uneven, with higher concentrations found in the base of the stem, followed by the lower internodes, growing points, heart tissue, leaf blades, and leaf veins and sheaths. The severity of the disease is directly related to the bacterial load in the plant. Externally, RSD-infected plants exhibit stunted growth, reduced stem diameter, and delayed development. Affected canes are highly sensitive to water stress, which exacerbates their slow growth during dry periods. Severely affected plants may show wilting or dry leaf margins. However, sufficient irrigation can mask these symptoms and reduce damage. Internally, two key signs are observed. First, the tissue below the growth point (within 1 cm of the node) turns orange-red, with color intensity varying by variety and influenced by nitrogen fertilizer application. Second, the vascular bundles in mature stems change from yellow to orange-red and eventually to dark red. This discoloration is most noticeable on the first to tenth nodes, especially between the third and eighth nodes. The discoloration typically remains localized at the nodes and rarely spreads to the internodes. In cross-sections, the discolored vascular bundles appear as dots, commas, or short stripes, while in longitudinal sections, they may form radial patterns. Not all varieties display these internal symptoms. The disease spreads primarily through contaminated planting material, such as cane cuttings and seedlings. Pathogens can survive in the stalks of infected seedlings or ratoon shoots, leading to infection in the next growing season. Diseased plants can spread the pathogen via tools like sugarcane knives, harvesters, and through root contact or leaf friction. Even diluted sugarcane juice (10,000 times) can be infectious, and contaminated tools remain infectious for up to seven days in shaded conditions. The longer the perennial growth period, the worse the disease becomes. To control RSD, the primary focus is on using disease-free seedlings and sterilizing them. Three common heat treatments are used: hot water treatment (50°C for 2 hours), hot air treatment (54–58°C for 8 hours), and steam treatment (53–54°C for 4 hours). Each method has its advantages and disadvantages in terms of efficiency, sprout damage, and moisture loss. Establishing a disease-free nursery is another critical step. After heat treatment, seedlings are planted in a controlled environment, and tools are disinfected using alcohol or flame. During cutting, all equipment must be kept separate and regularly sterilized to prevent cross-contamination. Tissue culture techniques, particularly using pathogen-free apical meristems, can produce virus-free seedlings that are then propagated for field use. Soil preparation, proper fertilization, and timely irrigation help enhance plant resistance. Before planting new crops, fields should be thoroughly cleaned, and all tools must be disinfected by boiling, steaming, or burning. Additionally, rodent control is essential to prevent them from damaging the cane and spreading the pathogen.

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