Pachymetra root rot

Pathogen and disease type. The disease is caused by the oomycete Pachymetra chaunorhiza, a specialized soil-borne pathogen that targets the root systems of sugarcane. It is a highly persistent pathogen capable of producing thick-walled oospores that can survive in the soil for extended periods, even in the absence of a host, making long-term control a significant challenge for farmers.

Host range. The pathogen is highly specific to sugarcane (Saccharum officinarum). It does not affect other major agricultural crops significantly, which leads to the accumulation of inoculum in soil when sugarcane is grown continuously on the same land for many years without adequate rotation or fallow periods.

Symptoms and signs. Typical symptoms include stunting of growth, yellowing of foliage, and reduced tiller numbers. The primary damage occurs below ground, where the pathogen destroys the root system, causing severe rotting of the primary and secondary roots. As the root system deteriorates, the plants struggle to anchor themselves and efficiently take up water and essential nutrients.

Conditions for development and impact. The development of the disease is favored by high soil moisture levels and moderate temperatures. The economic impact is significant, as it leads to lower biomass production, reduced sugar yield, and a shorter lifespan for the ratoon crops. Heavily infested fields may suffer from substantial gaps in the stand, necessitating expensive replanting.

Control and prevention measures. Integrated management of Pachymetra chaunorhiza involves several key tactics:

• Planting resistant or tolerant sugarcane cultivars, which is the most reliable control method.
• Implementing crop rotation with non-host crops to reduce soil inoculum levels.
• Improving soil drainage to prevent moisture buildup that favors oospore germination.
• Sanitation practices, including the use of clean planting material, to prevent the spread of the pathogen to new fields.