Trichothecium roseum
Trichothecium roseum has a worldwide distribution and is often isolated from decaying plant substrates, soil, seeds of corn, and food-stuffs (especially flour products). It is occasionally isolated as a saprophyte in the clinical laboratory.
RG-1 organism.
Trichothecium roseum conidiophores showing retrogressive conidial development.
Morphological description:
Colonies are moderately fast growing, flat, suede-like to powdery, initially white but becoming rosy, pink or orange with age. The conidiophores are indistinguishable from the vegetative hyphae until the first conidium is produced. They are erect, unbranched, often septate near the base, more or less rough-walled, bearing basipetal zig-zag (alternating) chains of conidia at the apex. Note: The conidiophore is progressively shortened with the formation of each conidium i.e. retrogressive conidial development. Conidia are two-celled ellipsoidal to pyriform, with an obliquely truncate basal scar, hyaline, smooth to delicately roughened and thick-walled.
Comment:
T. roseum should not be confused with Nannizzia nana. Colonies of the latter may be pinkish-buff in colour and also produce ovoid to pear-shaped, mostly two-celled macroconidia with thin, verrucose walls. However, N. nana usually produces a red-brown reverse pigment and the two-celled macroconidia are sessile and formed singly, they are not produced in basipetal chains as in T. roseum.
Molecular identification:
Summerbell et al. (2011) revised the genus using D1/D2 sequences for phylogenetic analysis and sequence based identification.
Key Features:
Hyphomycete, basipetal zig-zag chains of two-celled conidia showing retrogressive development where the conidiophore becomes progressively shorter.
References:
McGinnis (1980), Domsch et al. (2007), Rippon (1988), Samson et al. (1995), Summerbell et al. (2011).