Sclerotinia sclerotiorum is a plant pathogenic fungus and can cause a disease called white mold if conditions are conducive. S. sclerotiorum can also be known as cottony rot, watery soft rot, stem rot, drop, crown rot and blossom blight. A key characteristic of this pathogen is its ability to produce black resting structures known as sclerotia and white fuzzy growths of mycelium on the plant it infects. These sclerotia give rise to a fruiting body in the spring that produces spores in a sac which is why fungi in this class are called sac fungi (Ascomycota). This pathogen can occur on many continents and has a wide host range of plants. When S. sclerotiorum is onset in the field by favorable environmental conditions, losses can be great and control measures should be considered.
Hosts and symptoms
Sclerotinia sclerotiorum” (sometimes called white mold) is a fungal (Ascomycota) pathogen that infects a broad range of plants, affecting over 400 species across multiple families, including Brassicaceae (Cruciferae), Fabaceae (Leguminosae), Solanaceae, Asteraceae, and Apiaceae (Umbelliferae). Notably it is not known to infect grass species, and appears to be incapable of causing disease in clover. Common hosts of white mold are herbaceous, succulent plants, particularly flowers and vegetables. Sunflowers are common hosts for white mold. It can also affect woody ornamentals occasionally, usually on juvenile tissue. White mold can affect their hosts at any stage of growth, including seedlings, mature plants, and harvested products. It can usually be found on tissues with high water content and in close proximity to the soil. One of the first symptoms noticed is an obvious area of white, fluffy mycelial growth. Usually this is preceded by pale to dark brown lesions on the stem at the soil line. The mycelium then cover this necrotic area. Once the xylem is affected, other symptoms occur higher up in the plant. These can include chlorosis, wilting, leaf drop, and death quickly follows. On fruits, the initial dark lesions occur on the tissue that comes in contact with the soil. Next, white fungal mycelium covers the fruit and it decays. This can occur when the fruit is in the field or when in storage.
Importance White mold affects a wide range of hosts and causes sclerotinia stem rot. It is known to infect 408 plant species. As a nonspecific plant pathogen, diverse host range and ability to infect plants at any stage of growth makes white mold a serious disease. The fungus can survive on infected tissues, in the soil, and on living plants. It affects young seedlings, mature plants, and fruit in the field or in storage. White mold can spread quickly in the field from plant to plant. It can also spread in a storage facility throughout the harvested crop. Some crops it affects commonly are soybeans, green beans, sunflowers, canola, and peanuts. White mold is the most common pathogen that affects sunflower and has been found to cause reduction in yield throughout the world including the United States, northern Europe, Great Britain and Russia. Economically significant hosts include Vicia faba, for which Lithourgidis et al. have done extensive work over the years. Sclerotinia stem rot (or 'white stem rot', ) can cause economically significant yield losses in temperate climates, especially during cool and moist growing seasons. An analysis of soybean yields from 1996 to 2009 in the United States found that sclerotinia stem rot reduced yields by over ten million bushels in half of the studied growing seasons. During particularly bad years, these soybean yield reductions caused producers to lose millions of dollars. Compared to 23 common soybean diseases, sclerotinia stem rot was the second most problematic disease in the United States from 1996 to 2009. For soybeans, crop yields are inversely correlated with the incidence of Sclerotinia stem rot; an estimated 0.25 metric ton per ha is lost for each 10% increment of diseased plants.
Environment The pathogenic fungus Sclerotinia sclerotiorum proliferates in moist and cool environments. Under moist field conditions, S. sclerotiorum is capable of completely invading a plant host, colonizing nearly all of the plant's tissues with mycelium. Optimal temperatures for growth range from 15 to 21 degrees Celsius. Under wet conditions, S. sclerotiorum will produce an abundance of mycelium and sclerotia. Like most fungi, S. sclerotiorum prefers darker, shadier conditions as opposed to direct exposure to sunlight. For soybeans specifically, optimal conditions include canopy temperatures less than 28 °C and plant surface wetness for 12–16 h on a daily basis or continuous surface wetness for 42–72 h.
Life cycle
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