Sclerotinia sclerotiorum: Biology, Disease Cycle and qPCR Detection

Sclerotinia sclerotiorum belongs to the phylum Ascomycota and is a typical soil-borne fungal pathogen. One of its most distinctive features is the formation of sclerotia, which are hardened survival structures. Initially white, mature sclerotia develop a black արտաքին layer while maintaining a white الداخلي structure.

Sclerotia enable long-term survival under adverse environmental conditions and can persist in soil for more than three years. Under favorable conditions, they germinate to produce apothecia—small, cup-shaped fruiting bodies—that release large numbers of airborne ascospores. These spores serve as the primary inoculum for new infections and can be dispersed over long distances by air currents.

The disease cycle of S. sclerotiorum is closely associated with environmental conditions and agricultural practices. Sclerotia present in soil, plant debris, or contaminated seeds act as the main overwintering and oversummering structures, forming a persistent inoculum reservoir.

When temperatures range between 5–20°C and soil moisture is sufficient, sclerotia germinate and produce apothecia that release ascospores. These spores preferentially colonize senescent tissues such as aging leaves and fallen petals. From these initial infection sites, the pathogen invades healthy plant tissues through enzymatic degradation and mycelial expansion.

Epidemics are strongly favored by cool, humid environments, particularly at temperatures of 15–20°C and relative humidity above 85%. Prolonged rainfall, poor drainage, dense planting, and excessive nitrogen fertilization can significantly increase disease incidence and severity.

S. sclerotiorum is a necrotrophic pathogen that infects weakened or senescent plant tissues. After initial colonization, it secretes enzymes such as pectinases that degrade the middle lamella, leading to tissue maceration and soft rot.

Infected tissues often develop water-soaked lesions that rapidly expand. White, cotton-like mycelia grow profusely on the surface and within plant tissues. As the disease progresses, characteristic black sclerotia form inside or on infected tissues.

Stem infections are particularly destructive. Lesions may girdle stems, leading to tissue collapse, internal hollowing, and eventual plant death. Leaves may develop irregular, soft, grayish-brown lesions, while infected pods or fruits may rot and produce sclerotia, reducing both yield and seed quality.

The combination of white mycelial growth and black sclerotia is considered a hallmark diagnostic feature in field conditions.

Field diagnosis is primarily based on characteristic symptoms, including soft rot, white mycelial growth, and black sclerotia formation. However, laboratory confirmation is often required for accurate identification.

Microscopic examination reveals hyaline, septate hyphae. Sclerotia cross-sections show a dark rind and a lighter внутренний medulla. Induction of apothecia under controlled humidity and temperature conditions (15–20°C) provides further confirmation.

Molecular methods such as PCR offer rapid and highly specific detection. Probe-based real-time qPCR assays are particularly valuable for early detection, pathogen monitoring, and research applications.

Effective control of S. sclerotiorum requires an integrated management strategy. Crop rotation with non-host species such as cereals for at least 2–3 years can significantly reduce soil inoculum levels. Deep plowing helps bury sclerotia below the soil surface, limiting their ability to germinate.

Improving field conditions is also critical. Practices such as raised beds, proper plant spacing, removal of senescent leaves, and balanced fertilization can reduce humidity and disease pressure. Avoiding excessive nitrogen application helps prevent dense canopy formation that favors infection.

Chemical control should be applied preventively or at early stages of infection, particularly during high-risk periods such as flowering. Registered fungicides such as boscalid, iprodione, and procymidone can be used with proper rotation to prevent resistance development.

Biological control agents, including species of Trichoderma and Coniothyrium, have shown potential in suppressing sclerotia and reducing disease incidence. Advances in plant breeding and gene editing are also contributing to the development of resistant crop varieties.