Telial

Telial is an adjective used in mycology to describe structures or stages related to telia in rust fungi (order Pucciniales). A telium is a spore-bearing tissue or cluster on an infected plant, and it is the site where teliospores (also called teleutospores) are formed. Teliospores are typically thick-walled, durable, and often dikaryotic; they function as the overwintering resting spores for many rust species.

Telia usually appear later in the growing season, often as dark, dense, pimple-like or cushion-like clusters on leaves or stems. Following a period of teliospore development, germination occurs and the teliospores give rise to basidia that produce basidiospores, initiating the next stage of the rust life cycle. This makes the telial stage a key transition between the asexual uredinial oraecial stages and the sexual basidial stage.

In rust fungi that require two hosts (heteroecious species), the telial stage is typically followed by the production of basidiospores on the alternate host, which then infects the primary host to begin a new cycle. For self-contained rusts, the telial stage may link directly to the production of sexual spores on the same host.

Taxonomically, telial structures are used to identify species and understand disease dynamics. The term telial is used primarily in mycology and plant pathology and is distinct from, but related to, other spore-bearing stages such as uredinia, aecia, and basidia.