Pachymetra root rot of sugarcane

The most distinctive symptom of Pachymetra root rot is the severe reduction of the root system biomass, which is often observed upon excavation.

Infected roots exhibit browning and rotting, particularly in the large structural roots, which become soft and fail to anchor the plant effectively.

Above-ground symptoms include poor tillering, yellowing of leaves, and a general lack of vigor compared to unaffected stools in the same field.

During periods of dry weather, infected plants suffer more severely from moisture stress than healthy ones because their compromised roots cannot access deep water.

The distribution of the disease within a field is usually patchy, reflecting the movement and concentration of pathogen zoospores in the soil.

The disease is caused by the specialized oomycete Pachymetra chaunorhiza. It is a soil-borne pathogen that specifically targets the root system of the sugarcane plant.

This pathogen produces large, thick-walled oospores that allow it to survive in the soil for several years even in the absence of a host plant.

The life cycle of the organism is moisture-dependent; oospores germinate in response to water in the soil, producing sporangia and motile zoospores.

Zoospores are equipped with flagella, allowing them to swim through soil water films to locate and infect sugarcane root tips efficiently.

Once infection is established, the pathogen colonizes the root tissues, causing rapid necrosis and compromising the plant's ability to uptake nutrients.

The development and spread of Pachymetra chaunorhiza are strongly influenced by high soil moisture levels and poor drainage conditions.

Compacted soils often favor the accumulation of zoospores, providing an environment that promotes the infection of sugarcane root systems.

The disease tends to be more severe in fields where sugarcane is grown as a continuous monoculture, leading to a buildup of inoculum over time.

Mechanical movement of soil by farm machinery plays a crucial role in spreading the pathogen from infested fields to previously clean areas.

Optimal temperatures for the growth of this pathogen align with the environmental conditions typical for most sugarcane-producing regions.

The primary economic impact is a significant decrease in cane yield, which can result in severe financial losses for growers.

Reduced root health leads to stunted growth and lower sugar content, affecting the overall quality and profitability of the harvested cane.

Because the roots are damaged, plants are more susceptible to lodging, which creates challenges for mechanical harvesting and increases operational costs.

Early stool decline often forces farmers to replant fields sooner than expected, increasing expenses for cultivation and nursery materials.

The persistence of Pachymetra in the soil limits the choice of varieties, forcing growers to rely heavily on resistant genetics.

The primary and most effective strategy for managing Pachymetra root rot is the selection and planting of resistant sugarcane varieties.

Implementing fallowing or crop rotation cycles helps to reduce the inoculum density in the soil, providing a break in the pathogen's life cycle.

Improving field drainage is vital, as it reduces the duration of the soil saturation periods required for zoospore movement and infection.

Sanitation practices, such as cleaning machinery between fields, are essential to prevent the spread of contaminated soil to new plantations.

• Regular monitoring of root systems during the crop cycle.
• Application of soil amendments to improve soil structure.
• Avoidance of practices that lead to excessive soil compaction.