Bacterial leaf stripe of sorghum

The primary symptoms of this disease are narrow, elongated lesions or stripes that develop along the leaf veins. Initially, they appear light green or yellowish, later turning reddish-brown or nearly black.

Under high humidity, a bacterial exudate may appear on the surface of the lesions, which forms a thin, whitish or grayish crust upon drying. As the disease progresses, the tissues within the affected areas become necrotic and die.

In cases of severe infection, these stripes coalesce, covering a significant portion of the leaf blade, which leads to premature drying of the foliage. The disease typically starts on the lower leaves and moves upwards.

Unlike fungal leaf spots, bacterial stripes often have well-defined borders restricted by the leaf veins, giving them a linear appearance. When held against light, infected zones may look translucent or oily.

At early growth stages, symptoms may manifest as stunted growth and deformation of the first true leaves, often leading to reduced stand density and poor crop establishment.

The causative agent of the disease is the Gram-negative bacterium Paraburkholderia andropogonis (formerly classified as Pseudomonas andropogonis). This pathogen is a facultative parasite.

The microorganism primarily affects cereal crops, specifically sorghum, corn, and certain wild grasses. It is highly motile due to the presence of polar flagella.

The bacteria enter host tissues through natural openings, such as stomata, or through mechanical wounds caused by insect feeding, hail, or agricultural operations.

Inside the plant, the pathogen multiplies in the intercellular spaces, secreting enzymes that degrade cell walls and cause typical necrotic lesions. The infection is localized rather than systemic.

The bacterium can survive in infected seeds and crop residues for several years, making the seed material and the soil the primary sources of initial infection.

The disease develops most intensely in moderately warm and humid weather conditions. The optimal temperature range for rapid pathogen multiplication is between 20 and 28 degrees Celsius.

Frequent rainfall, fog, and high relative humidity promote the active spread of bacterial exudate across the field. Moisture is essential for the movement of bacteria from infected to healthy plants.

Poor agricultural practices, such as high planting density, create a microclimate with insufficient ventilation within the canopy. This traps moisture on leaf surfaces, which is critical for infection.

Injuries caused by insect pests create entry points for the pathogen. Outbreaks are significantly more common following hail or strong winds that cause micro-trauma to the leaf tissues.

Heavy application of nitrogen fertilizers, which leads to rapid, succulent growth and softer cell walls, makes plants more susceptible to pathogen penetration.

The primary damage from bacterial leaf stripe is a significant reduction in the functional leaf surface area. This disrupts photosynthesis, leading to reduced biomass accumulation.

Early infection can cause the death of young plants, reducing overall field emergence and crop density. This often necessitates replanting or results in substantial yield loss.

Reduced photosynthetic activity prevents plants from developing proper reproductive organs. Consequently, grain weight and fill quality are significantly diminished.

Bacteriosis negatively impacts the marketability of both grain and forage biomass. Infections during the flowering stage can lead to substantial yield deficits in grain production.

During massive epiphytotic outbreaks, sorghum yield losses can reach 20–30% or more, depending on the susceptibility of the hybrid and seasonal weather conditions.

The foremost control measure is the use of high-quality, certified seed material free from infection. Seed treatment with appropriate bactericides helps reduce the risk of initial infection.

Crop rotation is mandatory, as excluding sorghum from the field for 3–4 years allows for a significant reduction in the bacterial load in the soil and crop debris.

It is important to ensure thorough incorporation of crop residues into the soil immediately after harvest. This accelerates decomposition and reduces pathogen survival.

Proactive management of leaf-feeding insect pests prevents mechanical wounds, thereby reducing the routes for bacterial entry into the plant tissues.

Selecting resistant hybrids is the most effective economic management strategy. Additionally, avoiding excessive nitrogen fertilization helps maintain a balance of nutrients and structural cell integrity.