Morphological differences between aerial and submerged sporidia of bio-fongicide Pseudozyma flocculosa CBS 16788

Pseudozyma flocculosa is a fungus very useful and highly efficient as a biocontrol agent
against powdery mildew. The reproduction of this fungus occurs exclusively by asexual production
of conidia or sporidia that are the most suitable form for agricultural use and seems
to be the most resistant to storage conditions. Despite the advantages offered by P. flocculosa
in biological control, the use of this fungus use remains largely limited compared to that
of chemical fungicides, at least partly due to the difficulty to obtain sporidia resistant to
adverse environmental stresses in submerged culture conditions. Under solid-state and
submerged-state cultivation, P. flocculosa strain CBS 16788 produced different types of
sporidia. The submerged sporidia (SS) appeared relatively uniform in size, which was 15,
4 ± 1,6 μm μm long, and 2,8 ± 0.8 μm wide. The aerial sporidia (AS) varied in shape and
size, with a mean length of 8,2 ± 3 μm and width of 2,3 ± 0.6 μm. Under scanning and transmission
electron microscopy, the cell wall of submerged sporidia was thinner than that of
aerial spores, and the surface was smooth in contrast to the aerial sporidia that had a tendency
to have verrucous, brittle surface characteristics. The thickness of the aerial sporidia
wall is due to the presence of an outer layer rich in melanin. The sporidia germination was
compared on YMPD (yeast extract, malt extract, soy peptone, dextrose and agar) coated
coverslips. The aerial sporidia did not show germ tubes until 5 h of incubation, while the
submerged sporidia showed many germ tubes after the same time. The resistance against
the adverse environmental conditions in relation to the type of sporidia of P. flocculosa is
discussed