White Mold – Sclerotinia spp.
White mold, also known as Sclerotinia spp., is a species of mold that has been known to cause a number of diseases in plant species. White mold can generally be identified by its white cotton like mycelium. It can normally be found growing on the surfaces of infected aerial tissue.
White Mold Symptoms
The hyphae produce enzymes and oxalic acid, creating water soaked lesions, frequently with a distinct margin. Secondary symptoms such as wilting, bleaching, and shredding also can be observed on above-ground tissues including stems, leaves, petioles and reproductive organs.
At later stages of the disease, the cottony hyphae of the pathogen aggregate into (typically) pea-sized clumps of mycelium. These clumps eventually mature into hard black sclerotia, which are most commonly found on the outer surface of the diseased tissue, but sometimes inside of soft host tissues or cavities such as floral receptacles, fruits and the pith of stems.
White mold is a monocyclic disease, meaning that it has only a primary cycle of infection, and once the host tissue is diseased, it is not contagious (i.e., spore-producing) within the same season. While white mold may not be as harmful to humans as black mold it can still be dangerous. Plant to plant spread of S. sclerotiorum and S. minor may occur occasionally, is usually is a rare occurrence.
Most severe disease situations in a field develop from sclerotia that are local within the field soil. In the case of carpogenic germination of sclerotia, ascospore releases into the air typically occur at ground level under closed canopies, and consequently, sharp foci of infection are often observed within the field. Nonetheless, infections initiated by wind-disseminated ascospores from another location have been observed occasionally
Introduction of the pathogen from outside sources also may occur by contaminated machinery, mass movement of water, and by wind-blown crop debris. In some hosts, seed may be internally infected with mycelium of Sclerotinia, or inadequately cleaned seed may be contaminated with seed-sized sclerotia. Numerous broadleaf weeds also are hosts of white mold, and may contribute to a persistence of sclerotia within a field.
Sclerotinia species are homothallic (self-fertile), and distinctly clonal populations of S. sclerotiorum and S. minor have been found in infested fields. Different clonal groups can occur together, and in some cases, clonal groups have been found to differ in pathogenic aggressiveness.