SPOTS on cotyledons, leaves, and petioles, at first pale green, later yellow, finally brown, at first scattered, subcircular to prolate, up to 5 mm diam, later frequently confluent and forming extensive lesions.
PYCNIDIA (p) crowded on the lesions, immersed or slightly erumpent, subepidermal, unilocular, globose to subglobose, sometimes slightly flattened, 70-150 µm diam, yellow brown to dark brown, with a subcircular to elliptical, ostiolum, 23-60 µm diam.
Wall (w) 3-5 µm thick, composed of thick-walled, yellow brown to dark brown, angular cells.
Conidiogenous cells (cc) phialidic, hyaline, sessile on the inner wall surface of pycnidia.
CONIDIA (c) hyaline, filiform or slightly cylindrical, usually slightly curved, 0-7-septate, usually 4-septate, 25-60 x 1.5-3 µm.
PLANT HOST AND DISTRIBUTION. Septoria apiicola is the causal agent of late blight of Apium graveolens L.
This fungus has a worldwide distribution (Teterewnikowa-Babajan 1987).
NOTES. Septoria apiicola also form pycnidia on seeds, and this is the main means of dissemination of the fungus. Conidia from these pycnidia attack the seedlings.
The weather conditions favourable to germination of conidia and their dissemination ar 18-24oC, as well as rainy and windy days.
The conidia of S. apiicola penetrate into leaves of its plant host through the cuticule, rarely through stomata.
Septoria apiicola overwinters in seeds and plant debris.
Teterewnikowa-Babajan D. N. 1987. Griby roda Septoria w SSSR. Izdatelstwo An Armianskoj SSR, 480 pp.