Effect of the paramorphogens, 3-O-methyl-d-glucose, glucosamine and l-sorbose, on growth and morphology of Botrytis fabae

The paramorphogens, 3-O-methyl-d-glucose, glucosamine and l-sorbose induced reversible morphological changes (increase in hyphal branching and the formation of dense, slowly expanding colonies) in Botrytis fabae. 3-O-methyl-d-glucose was not used as a carbon source for growth by B. fabae, even following growth on glucose. Glucosamine was not used for growth when it was the sole carbon source in the medium, but diauxic growth was observed when B. fabae was cultured on a mixture of glucose and glucosamine. By contrast, l-sorbose was used for growth by B. fabae even when it was the sole carbon source in the medium. The three paramorphogens did not affect the specific growth rate or yield coefficient of B. fabae cultured on 5 mM glucose, and therefore cannot be regarded as inhibitors of fungal growth.

All the paramorphogens reduced hyphal compartment length, hyphal growth unit length and colony radial growth rate, and significant correlations were observed between intercalary compartment length and hyphal growth unit length, and between hyphal growth unit length and colony radial growth rate. The results show that hyphal branch frequency is an important determinant of peripheral growth zone width and hence of colony radial growth rate. The effects of the paramorphogens on mycelial morphology (a) were reversed by increasing the glucose concentration in the medium, (b) were not dependent upon glucose exhaustion, and (c) could not be explained in terms of a reduction in the water activity of the medium.