Scytalidium ganodermophthorum

Scytalidium ganodermophthorum was first identified in Korea as yellow rot, a disease affecting Ganoderma lucidum.[1] In 1996, Jong-Kyu Lee et al. identified it as a fungal pathogen and categorized it as Xylogone sphaerospora.[1] However, in 1998, Se-Jong Oh and researchers at Kangwon National University recategorized the fungus as Arthrographis cuboidea based on morphological characteristics.[2] Researchers returned to the topic in 2010 and reclassified the fungus as Xylogone ganodermophthora. It is most frequently referred to by its anamorph name, S. ganodermophthorum.[3] DNA analysis suggests that S. ganodermophthorum is part of a clade that includes X. sphaerospora, A. cuboidea and Scytalidium lignicola within Scytalidium, but the position of the clade within Leotiomycetes is unknown.[3]

The fungus is a saprobe and opportunistic fungal pathogen found in wood and soil.[2] Infected wood exhibits a greenish-yellow color with brown border lines.[1][2] Eventually, infected wood turns black and disintegrates as S. ganodermophthorum consumes it.[1] Fungal colonies range from pale yellow to yellow green on agar plates.[2]

This species reproduces sexually and asexually. In sexual reproduction, it produces small yellow fruiting bodies known as ascocarps. These ascomata are 45-95 μm spheres with dark, thick walls.[1] Within the ascomata are many asci; these asci are thin-walled and disintegrate easily.[1] The ascospores contained in the asci are smooth, refractive spheres with a glassy appearance, about 3.6-4.3 μm in diameter.[1] Most ascospores produced by the ascomata are not viable.[4] In asexual reproduction, the fungus forms conidiophores through mitosis. Conidiophores are septate and break into cylindrical arthrospores 3-6 μm long and 3-4 μm wide.[1] Both sexual and asexual spores are disseminated through soil and wood.[4]

Yellow rot first emerged in Korean lingzhi cultivation beds the late 1980s.[1] It rapidly spread through established growing facilities; Chulwon cultivation areas experienced a 61% incidence of the disease and Kanghwa areas experienced a 94% incidence rate.[2] The Shintanjin growing site was also impacted, although the extent of infection was not reported.[1] Newer growing sites in Moonkyung and Hongsung were not infected as of 1998.[2] By 2003, 17 growing sites all over Korea had reported yellow rot.[3] S. ganodermophthorum contamination causes severe yield and profit losses, is difficult to eliminate, and can prevent future use of cultivation spaces.[3] So far, yellow rot has only been reported in Korean cultivation houses.[3]

Diseased G. lucidum display the yellow-green color of S. ganodermophthorum at the base of the mushroom and pilei are malformed.[3] The change in color is due to the accumulation of S. ganodermophthorum mycelia. S. ganodermophthorum mycelia destroys the lingzhi mushroom.[2] Inoculation of S. ganodermophthorum and G. lucidum on agar plates results in the arrest of G. lucidum growth and eventual death.[1] Non-volatile compounds secreted by the pathogen are inhibitory of the crop mushroom's growth by themselves.[2]

Research into S. ganodermophthorum beyond its status as a fungal pathogen began in the 2000s.[5] The Applied Mycology Lab at Oregon State University is currently researching applications of S. ganodermophthorum for spalting.[6] This species produces a water-insoluble yellow pigment.[7] The structure and components of this pigment are still unidentified. Due to its properties as an insoluble pigment, this fungal pigment is being examined as a naturally-derived aniline dye replacement.[6] There are several methods of pigmenting wood with this fungus. In the cut-wood inoculation method, at 12 weeks, the yellow pigment completely saturated the wood samples.[7] According to the woodchip-agar/chemical solvent extraction method created by Robinson, dichloromethane is the best solvent for extracting this pigment.[8][9] The fungus can also be grown in a liquid culture and extracted with dichloromethane.[6] Beyond woodworking, this pigment is also being investigated for its potential as a fabric and paint dye.[10][11] On fabric, this pigment shows greater colorfastness for both light and washing compared to contemporary commercial dyes.[12][10] Mordanting increases the colorfastness of the yellow pigment under UV radiation.[12] Natural oils (such as linseed oil) can be used as nontoxic alternative carriers compared with dichloromethane, but the pigment is not stable in such carriers.[13]

• Spalting
• Scytalidium (genus)
• Mushroom dye