Paspalum smut

The main sign of infection is the replacement of Paspalum seeds with specific smut galls filled with dark fungal spores.

Visually, the disease becomes apparent during the heading period. Instead of normal spikelets, deformed structures covered with a grayish or brownish membrane develop on the inflorescences.

As they mature, the membrane of the galls ruptures, and a mass of black spores (teliospores) is released, contaminating surrounding plants and the soil.

Infected inflorescences often have an atypical shape, appearing shorter or denser than healthy ones, which aids in identifying the disease at early stages.

• Darkening and deformation of individual spikelets.
• Presence of a powdery spore mass upon rupture of the gall.
• Reduction in overall seed productivity on the affected area.

The causal agent of this disease is the basidiomycete fungus Sporisorium paspali-notati, which belongs to the order of smut fungi. This is a highly specialized pathogen that primarily infects the reproductive organs of the host plant.

The biology of the fungus is closely linked to the flowering phase of the grass. The infection invades the plant ovary, where, during mycelial development, it completely replaces the grain tissues with a mass of spores.

The fungus survives as teliospores on the soil surface or on plant debris, which later serve as the primary source of infection for new seedlings or mature plants.

Unlike other smut species, this pathogen exhibits high host specificity, infecting mainly Paspalum notatum, which limits its spread to other grass species.

The life cycle of the pathogen requires strict adherence to specific temperature and humidity ranges for successful spore germination and subsequent penetration into plant tissues.

Disease development is most intense under conditions of moderate temperature and high air humidity during the Paspalum inflorescence formation period.

Heavy rainfall or dew during critical plant development phases facilitates rapid spore germination and their active dispersal by wind and rain.

Poor agricultural practices, such as soil compaction and excessive irrigation, create a favorable microclimate in the canopy that promotes pathogen accumulation.

Prolonged periods of standing moisture in the ground layer facilitate more frequent infections, as spores require a film of water to germinate.

The presence of large amounts of unremoved plant debris in the field also maintains a high inoculum level over several consecutive seasons.

The primary danger of smut is the total loss of marketability and viability of seed material, making it unusable for planting purposes.

The disease leads to a sharp decline in Paspalum seed yields, causing significant economic losses for seed production farms.

Massive spore dispersal significantly complicates pathogen control in subsequent years, as the soil receives a strong reserve of primary inoculum.

Indirect harm includes reduced aesthetic appeal and forage quality of the grass cover if Paspalum is used in pastures or lawns.

Severe infection can weaken the plant's overall immunity, making it more susceptible to other diseases and unfavorable environmental factors.

The primary control measure is to use only healthy, certified seed material that shows no signs of smut infection for planting.

An important practice is maintaining crop rotation and timely removal of infected plants from the plot to prevent further spore dispersal.

Applying fungicidal seed treatments before sowing can significantly reduce the risk of primary infection in Paspalum seedlings.

Regular mowing of the grass before the seed formation phase helps eliminate the possibility of mass spore spread within the area.

Maintaining optimal water balance and improving soil drainage help reduce humidity in the canopy layer, which suppresses pathogen activity.