Rhizoctonia Life Cycle

Life Cycle

Rhizoctonia solani has a decomposer or saprophytic phase and a parasitic phase and can be active in both simultaneously. Previous crop stubble is a food source and host for the decomposer (saprophytic) phase, allowing the fungus to survive year-round. 

Rhizoctonia can develop under dry soil conditions, below the permanent wilting point, and survive dry summers, enabling it to outcompete other root rot pathogens. Infections and crop loss are often severe following dry conditions. Significant rainfall of more than 20mm in seven days can help reduce Rhizoctonia inoculum. Unfortunately, warm, moist conditions are conducive to the growth of other pathogens in the root rot complex. 

The seedling stage is the most susceptible to Rhizoctonia infections, and plants become less vulnerable as they age. Rhizoctonia infections may be more prevalent in early-seeded or deep-seeded crops, as deep seeding increases the length of the hypocotyl and the opportunity for infection. 

• These fungi are common in the soil, and infection is more likely if the soil around the seed is excessively wet. Warm and moist conditions generally favour Rhizoctonia, but cold and damp soil is also detrimental because the cool temperatures slow plant development and add additional stress. 

• Wet Conditions: Wet feet stress plants and reduce rhizobial activity. Root rot fungi need water to germinate and infect roots. 
• High Soil Temperatures: High soil temperatures (24–30˚C) cause higher infection rates.
• Cool Temperatures Early in the Season: Slow plant growth and slow nitrogen availability from organic matter.
• Shortened Rotations: Increase the level of pathogens in soil.
• Heavy Textured Soils: More prone to waterlogging and compaction.
• Soil Compaction: Root growth impeded and less aeration.
• Nutrient Deficiency: Slows seedling growth and weakens the plant.

Symptoms

Rhizoctonia infection typically occurs close to the soil surface. Symptoms begin as reddish-brown sunken lesions on the hypocotyl or stem that remain firm and dry at the soil line. Rhizoctonia infections are the most aggressive from 24–30°C under various soil moisture conditions. Emergence to 8-leaf infected seedlings may wilt and die as lesions grow and rot through the hypocotyl. If plants survive, they will remain stunted and are less productive.

Later-season symptoms may be difficult to distinguish from a Fusarium infection.