Conidiation

Conidiation is a mode of asexual reproduction in fungi in which conidia (conidiospores) are produced externally on specialized hyphae called conidiophores. Conidia are typically dispersed by wind, water, or contact, enabling rapid colonization and persistence under favorable conditions. The process is regulated by developmental pathways that generate distinct types of conidia.

Conidiogenesis occurs by two main developmental routes: blastic conidiogenesis, in which a daughter cell forms by outgrowth and separation from a parent cell, and thallic conidiogenesis, in which a cross-wall partitions a hyphal segment, generating a conidium. Conidia may be produced by phialides (phialidic conidiation), which generate conidia through repeated openings, or by annellides (annellidic conidiation), which leave ring-like scars as successive conidia are produced. In many fungi, conidia are formed on aerial conidiophores and arranged in chains or heads.

Conidiogenesis may proceed in acropetal or basipetal directions along the conidiophore, indicating the spatial order of conidium maturation. Fungal genera vary greatly in conidial morphology, with shapes ranging from unicellular spheres to multicellular, pigmented forms. Aspergillus and Penicillium, for example, produce characteristic conidial structures on vesicles and metulae; others produce conidia directly from hyphae.

Conidiation is central to fungal ecology and evolution, enabling rapid spread and survival in fluctuating environments and supporting numerous plant and human pathogens. It also provides critical characters for taxonomic identification and laboratory cultivation. Many fungi exhibit both asexual (conidial) and sexual (teleomorph) stages, though some lineages rely almost entirely on conidiation for propagation.