About Karnal Bunt
Karnal bunt is a fungal disease caused by the fungus Tilletia indica. This fungus produces teliospores that overwinter for at least 4 to 9 months at a time. However, note that teliospores are capable of surviving in soil for years on end. After this dormancy period, teliospores are spread through wind, plant debris, farm equipment, and splashing rain. After heading, teliospores produce sporidia, which are then spread to the plant where sporidia penetrate the stomata and grow at the base of the kernel. After the infection has advanced to its later stages, teliospores will germinate in the soil and sporidia will become airborne, ready to look for a new host.
Karnal Bunt Identification and Habitat
Newly developing kernels are infected at random and are typically only partially affected, hence the disease’s alternative name “partial bunt”. Not all heads from a plant will be affected by the pathogen. Identifying the disease can be difficult as hosts show no symptoms until they’re close to maturing. Infected kernels become dark in colour and smell fishy. On the kernel, spores appear as a black, powdery mass. Although most crops are partially affected, severely affected kernels can become entirely covered in the black spore mass. Careful inspection is required as this disease can be confused with related diseases.
Weather conditions are critical in the development of karnal bunt. High relative humidity (70% or higher) and frequent rains favor disease development. By increasing humidity and wet periods, irrigation increases the chance of infection and spread of disease. Lengthy wet periods allow the teliospores to germinate and develop effectively. Air temperatures of 64° to 72°F and soil temperatures of 63° to 70°F are most suitable for disease development, and tend to cause higher severity of infection. During fallow periods, dry soil and moderate temperatures help spores overwinter.
Karnal bunt Management and Control Methods
Using disease-free seed is crucial to avoid introducing the fungus to previously unaffected areas. Too much irrigation and high levels of nitrogen in the soil favor disease development. When working on crops, using sanitary farming equipment is highly important to limit the dispersal of the pathogen. Crop rotation can be effective, but be cautious because the fungus can survive in the soil for about 4 years. Disinfecting fields of teliospores can help reduce chances of future infection, but teliospores can still be reintroduced from nearby fields. Changing planting dates so that heading takes place during non-suitable weather conditions for disease development can also be effective.
Infection by airborne sporidia can be controlled using foliar fungicides. Seed treatments have been shown to be ineffective at controlling karnal bunt. Before using fungicides, be sure to read labels for cautionary advice and application guidelines.