The main damage caused by damping-off is reduction of the stand, meaning it is very often necessary to replant, which increases the crop's production costs. Necrosis ensues, spreads, and forms dark-brown patches variable in size. In favourable conditions, these fungi cause necrosis of the young tissues and softening of the stem, cotyledons, and roots. In leaf blight diseases, the tips and margins turn yellow (chlorotic). Damping-off may occur during germination or establishment of the plant (seedling phase), due to the occurrence of fungi inhabiting the soil, or associated with the seeds. The fungus may reduce the stand of the plants. Spherical sclerotia, which are initially white and then darken, also form on this vigorous mycelium. In highly humid conditions, white mycelium growth is observed on the plant’s stem, which may also develop on the adjacent soil. As the damage progresses, it causes darkening and rotting of the stem, resulting in the destruction of the cortex and the main root. Symptoms begin with brown, aqueous lesions on the stem. Severely affected plants present girdling of the stem, which causes wilting of the upper part, necrosis, loss of leaves, and death of the plant. As a consequence, leaves higher up in the plant start yellowing. Both the sclerotia and the mycelium are a source of inoculum, as the fungus can survive saprophytically in agricultural debris in the form of mycelium, which then forms the sclerotia. The sclerotia have a resistance structure resulting in longevity of more than five years in the soil, in a dry environment. The fruiting bodies are asexual and there are no spores, forming dark brown or black sclerotia which are rounded, irregular, or compact. The telemorphic phase corresponds to the basidiomycetes Athelia rolfsii, but this is rarely observed. The sclerotia can survive in the soil for a minimum of a year. In favourable conditions, the sclerotia can germinate in two forms, hyphal or eruptive, causing infection in the plants. Injuries make a host more susceptible, but it can invade via direct penetration, generally close to the surface of the stem. In addition, germination is induced by the presence of volatile compounds emanating from crop residues in the soil, organic material without suppressive effect, since the fungus needs to grow saprophytically on organic substrate before acting as a pathogen. In the anamorphic form it does not produce spores or fruiting bodies it only forms hyphae. Very humid soils favour development of the fungus. ![]() The ideal pH range for germination is between 2.6 and 4.4, but it can occur between 2.6 and 7.7. The favourable conditions for the development of the pathogen are temperatures between 25 and 30 ✬, relative humidity of over 90%, and a soil pH of under 7. They can be dispersed via water, agricultural tools, and contaminated seeds. They are round and their diameter varies from 0.4 to 2 mm. When the mycelium is young it is white later it darkens. The fungus Athelia (Sclerotium) rolfsii is characterized by the production of vigorous mycelium.
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