Phytotoxins, sesquiterpenoid

Sorokinianin, an unusual sesquiterpenoid, is isolated from Bipolaris sorokiniana, a fungal phytopathogen that causes spot blotch or foot and root rot diseases in wheat, barley, and oat. It is biosynthesized from phytotoxic prehelminthosporol and C3 unit derived from oxaloacetic acid.328 Prehelminthosporol itself was isolated as a phytotoxin of Helminthosporium sativum. Sorokinianin is more phytotoxic than prehelminthosporol in inhibiting the germination of barley seeds. 

The fungus Botrytis cinerea—a serious plant pathogen (Chapter 8)— produces a group of sesquiterpenoid fungal metabolites known as the botryanes. Botrydial (5.38), which is the major phytotoxin, and dihydrobotrydial (5.39) were first isolated in 1974. Their structures were established by X-ray crystallography. 

Capsidiol (31), an eudesmane sesquiterpenoid, is formed from i , -famesyl pyrophosphate by the pepper Capsicum annuum when inoculated with the spores of Monilia fruticola (Threlfall and Whitehead, 1991). The mode of incorporation of acetate suggests a biosynthetic scheme in which the angular group has undergone a 1,2 shift, rather than involving spiran intermediates, as are involved in the biosynthesis of other solanaceous phytotoxins (Brooks and Watson, 1985 Harbome, 1982 Stoessl, 1982). 

A number of other sesquiterpenoid phytotoxins and mycotoxins have been reviewed (Herout, 1970, 1973 Stoessl, 1981). 

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