BIOLOGY
Related pathogens include: Sclerotinia libertiana and Whetzelinia sclerotiorum.
Species of the genus Sclerotinia can function either as soilborne or airborne pathogens. Infections of above ground plant parts occur when sclerotia germinate to produce apothecia which in turn release airborne ascospores), At the soil-line, infection may result from either ascospore or sclerotial infection, while below ground infections result from mycelium produced from sclerotia.
Approximately 90% of the life cycle of Sclerotinia species is spent in soil as sclerotia. At certain times of the year, depending on the inherent nature of the fungus and various environmental factors, the sclerotia germinate and form either mycelium which can infect a host, or an apothecium. Infection of host plants by mycelium can occur at or beneath the soil-line. Sclerotia germinate in the presence of exogenous nutrients and produce hyphae which invade nonliving organic matter, forming mycelium which then infects living host tissues. Penetration of the host cuticle is achieved by mechanical pressure. Mycelium infection is unlikely to infect plants located more than 2 cm from a sclerotium.
Carpogenic germination produces an apothecium which releases ascospores that disseminate by air. Generally, 10-20 C is the optimum temperature range for carpogenic germination. Under favorable conditions, including adequate moisture, ascospores germinate within 3-6 hours of release. In one study, apothecia collected from the field discharged ascospores continuously for seven days in the laboratory. Ascospores infect nonliving host tissues, germinate, and inundate the nonliving plant part with mycelium. Then, the fungus invades healthy plant tissues with mycelium. After the plant or plant part dies, sclerotia are formed either on or in the plant. The sclerotia return to the soil for a "resting" period (which can be weeks or years) before they become active, which requires the appropriate environmental conditions.
Sclerotia are the structures which allow species of Sclerotinia to survive for long periods of time under adverse conditions. The black, melanized rind appears to act as a protectant from invasion by microorganisms. Soil temperatures, pH, and moisture appear to have little direct effect on their survival, though the combination of high temperatures and high moisture appears to encourage the degradation of sclerotia near the soil surface.
Many microorganisms in the soil have a detrimental effect on sclerotia. Coniothyrium minitans and some Trichoderma spp. have been established as destructive mycoparasites of Sclerotinia spp. It appears that secretion of á-1,3 glucanase from C. minitans (and possibly from some Trichoderma spp.) degrades and lyses sclerotial tissues.
BIOLOGYRelated pathogens include: Sclerotinia libertiana and Whetzelinia sclerotiorum.Species of the genus Sclerotinia can function either as soilborne or airborne pathogens. Infections of above ground plant parts occur when sclerotia germinate to produce apothecia which in turn release airborne ascospores), At the soil-line, infection may result from either ascospore or sclerotial infection, while below ground infections result from mycelium produced from sclerotia.Approximately 90% of the life cycle of Sclerotinia species is spent in soil as sclerotia. At certain times of the year, depending on the inherent nature of the fungus and various environmental factors, the sclerotia germinate and form either mycelium which can infect a host, or an apothecium. Infection of host plants by mycelium can occur at or beneath the soil-line. Sclerotia germinate in the presence of exogenous nutrients and produce hyphae which invade nonliving organic matter, forming mycelium which then infects living host tissues. Penetration of the host cuticle is achieved by mechanical pressure. Mycelium infection is unlikely to infect plants located more than 2 cm from a sclerotium.Carpogenic germination produces an apothecium which releases ascospores that disseminate by air. Generally, 10-20 C is the optimum temperature range for carpogenic germination. Under favorable conditions, including adequate moisture, ascospores germinate within 3-6 hours of release. In one study, apothecia collected from the field discharged ascospores continuously for seven days in the laboratory. Ascospores infect nonliving host tissues, germinate, and inundate the nonliving plant part with mycelium. Then, the fungus invades healthy plant tissues with mycelium. After the plant or plant part dies, sclerotia are formed either on or in the plant. The sclerotia return to the soil for a "resting" period (which can be weeks or years) before they become active, which requires the appropriate environmental conditions.Sclerotia are the structures which allow species of Sclerotinia to survive for long periods of time under adverse conditions. The black, melanized rind appears to act as a protectant from invasion by microorganisms. Soil temperatures, pH, and moisture appear to have little direct effect on their survival, though the combination of high temperatures and high moisture appears to encourage the degradation of sclerotia near the soil surface.Many microorganisms in the soil have a detrimental effect on sclerotia. Coniothyrium minitans and some Trichoderma spp. have been established as destructive mycoparasites of Sclerotinia spp. It appears that secretion of á-1,3 glucanase from C. minitans (and possibly from some Trichoderma spp.) degrades and lyses sclerotial tissues.
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