Effects of paramorphogens and 2-deoxy-d-glucose on development of lesions of Botrytis fabae on Vicia faba

An assessment was made of the efficacy of paramorphogens (3-O-methyl-d-glucose, glucosamine and l-sorbose) and 2-deoxy-d-glucose as antifungal agents to control chocolate spot disease of broad bean (Vicia faba) caused by Botrytis fabae. At the concentrations tested, 3-O-methyl-d-glucose, glucosamine and l-sorbose showed no fungistatic or fungicidal activity in vitro, but 5 mM 2-deoxy-d-glucose was fungistatic. The rates of conidial germination and germ-tube growth of B. fabae were reduced in vitro and in vivo by 3-O-methyl-d-glucose, glucosamine and 2-deoxy-d-glucose, but not by l-sorbose. The presence of glucose or l-sorbose increased the development of lesions of B. fabae on detached leaves of V. faba, but 0.1 mM 2-deoxy-d-glucose, 1 mM glucosamine and 40 mM 3-O-methyl-d-glucose prevented or reduced lesion development. In the absence of antifungal agents, penetration pegs of B. fabae were formed directly from germ-tube apices or from appressorium-like swellings. However, appressorium-like swellings were not observed on the surface of leaves treated with 3-O-methyl-d-glucose, glucosamine or 2-deoxy-d-glucose. The paramorphogens did not elicit phytoalexin (wyerone and wyerone acid) production, but phytoalexins were elicited by 10 mM 2-deoxy-d-glucose.The antifungal activity of wyerone acid was increased in the presence of 3-O-methyl-d-glucose, glucosamine and 2-deoxy-d-glucose.