Hyphal coil morphology and its relationship to thromboplerous hyphae in Rhizopogon roseolus

While observing mycelial features of the ectomycorrhizal fungus Rhizopogon roseolus, we noted the formation of hyphal coils in laboratory cultures. The coiled hyphae initially formed at the hyphal tip in the presence or absence of the plant host (Pinus thunbergii), on both rich and poor modified Melin-Norkrans media. Hyphal coils formed from the hyphal tips toward the middle of the hyphae, with rope-like hyphal strands fused as extensive circular coils. Hyphal coils were generally oval and circular. Coils were composed of 1-5 layers of hyphae. Presence of the host had a significant impact on the diameter of the coil loops, which was consistently wider without the host than with the host present on both media. In addition, the terminal part of the mature coils was melanized and separated from the unmelanized coil by a septum. The melanized coils resembled thick condensed hyphae and were detached and scattered throughout the fungal colony. The observation of morphological characteristics suggested that mature coils detached into the mycelia were thromboplerous hyphae. This is the first report on hyphal coil morphogenesis and its potential relationship to the initial development of thromboplerous hyphae.