Damping off is a severe issue for tomato growers, as it can quickly spread and result in the widespread death of seedlings. It is caused by various fungi, such as Pythium, Rhizoctonia, and Phytophthora, that attack the seeds, stems, and roots of tomato plants. The disease is most prevalent in humid conditions, especially when the soil is cold and wet, and young seedlings or plants are the most susceptible.
The symptoms of damping off include plant death as if cut off at the base, and the spread of the disease can be rapid through the air, moving from one seed tray or garden row to another. This makes it a significant concern for tomato growers, as an outbreak of damping off can have devastating effects on the start of the growing season.
Damping off Disease Management in Tomato
The Causal Organism of Damping-off Disease
Pythium aphanidermatum is a casual organism, as well as several other fungi, including species of Rhizoctonia, solani, Fusarium, Botrytis, Sclerotinia, Sclerotium, and Phytophthora, can cause the decay of seeds and seedlings in tomato plants and lead to Damping Off. Environmental factors such as high humidity levels, cool soil, rich potting soils, and planting too deeply, can encourage the growth of these fungi and increase the risk of Damping Off.
The Disease Cycle of Damping-off Disease
The disease cycle of Damping-off disease is as follows:
- Pythium aphanidermatum and other soilborne fungi can be found in small amounts of soil and dirt, including reused seed trays and benches.
- Fungal fragments or mycelium will colonise the soil in the trays after the seed is planted and watered.
- When seedlings are kept very wet, the likelihood of an outbreak of damping-off increases.
- Damping-off pathogens can colonise the soil in seed trays via openings in the tray bottom on dirty greenhouse benches.
- When one seedling in a seed tray develops symptoms, neighboring seedlings are frequently infected, resulting in an epidemic of damping-off disease.
Causes/Conditions Favorable for Damping-off Disease Spread in the Field
Favorable conditions for the damping-off disease include high humidity, high soil moisture, overcast weather, and low temperatures below 24°C for a few days. Crowded seedlings, excess moisture from high rainfall, poor soil drainage, and high concentration of soil solutes can also contribute to the growth and spread of the disease. These conditions can weaken the seedlings, making them more susceptible to attack from pathogens.
Symptoms of Damping-off Disease
- Root decay of stems at or near the soil line.
- Mold growth at the soil line
- Stunted growth of young seedlings
- Wilting of leaves and seedling stems.
- Discoloration of leaves and newly emerged seedlings to grayish or brown
- Softening and thinning of infected stems, appearing almost string-like.
- Pre-emergence phase: seedling death just before reaching the soil surface, complete rotting of seedlings, death of young radical and plumule.
- Post-emergence phase: infection of young, juvenile tissues of the collar at ground level, resulting in soft and water-soaked tissue, toppling over, or collapse of seedlings.