Chemical structure of two phytotoxic exopolysaccharides produced by Phomopsis foeniculi

The two main exocellular polysaccharides produced in vitro by Phomopsis foeniculi, a fungal pathogen of fennel, were isolated and characterized by chemical and spectroscopic methods as a galactan with the known structure [→6)-β-d-Galf-(1⃗5)-β-d-Galf-(1⃗5)-β-d-Galf-(1⃗]n and a mannan. The latter consists of a backbone of α-(1→6)-linked mannopyranose units. Almost all of these are branched at the 2 position with arms containing 2- and 3-linked mannopyranose units. The crude polysaccharide fraction and its components, galactan and mannan, showed phytotoxic effects, i.e. chlorosis, necrosis and/or wilting, on fennel and on two non-host plants, tobacco and tomato.