The kinetics of pycnospore liberation in Septoria tritici

Productivity and rate of liberation of spores from pycnidia of Septoria tritici on green detached flag leaves of field origin and from pycnidia on artificially inoculated wheat seedlings were studied. About 40% of the total spores within a pycnidium were exuded after the initial wetting, but the final percentage of spores which oozed naturally from the pycnidium ranged from 60 to 80% of the total spores, depending on the wheat cultivar and the environmental conditions in which the infected host was grown. The pycnidia were ellipsoid and their volume was calculated for both dried and wet pycnidia. The volume of wet pycnidia varied within the range of 0.012 to 0.019 mm3, which is about a 30% increase over the dry pycnidia, whose volume varied within the range of 0.003 to 0.006 mm3. The correlation between pycnidial volume and total number of pycnospores per pycnidium was non-linear. Wetting and drying treatments had little effect on pycnospore production and liberation rate, and did not cause the production of new pycnidia on detached green leaves.