Fungal Diseases of the Gramineae

barley, oats and rice provide a staple food for a substantial portion of the world s population. Consequently, their fungal diseases, and their means of defence against them, have attracted considerable attention. 

Fungi of the genus Helminthosporium are responsible for several leaf spot and other diseases of cereals and grasses. After the initial work on their metabolites had been reported, many of these organisms were reclassified as Bipolaris species. The perfect stage of some of these fungi is Cochliobolus and hence there can be confusion as to the source of a metabolite. 

The pigmentation associated with some of these fungi has been associated with anthraquinone formation and has been described in Chapter 7. However, the phytotoxicity has been attributed at least in part to the formation of 

The fungus H. carborum selectively attacks certain types of maize. It has been found to produce a host-specific toxin, HC-toxin, which has been shown to be a cyclic tetrapeptide, cyclo-[(2-amino-9,10-epoxy-8-oxodecanoyl)-alanyl-alanyl-prolyl]. This is one of several cyclic tetrapeptides that affect higher plants. 

These crops possess constitutive allelochemicals that provide protection against attack by fungal pathogens. Graminaceous plants contain the hydrox-amic acids l,4-benzoxazin-3(4//)-ones DIMBOA (8.33) and DIBOA (8.34) and related benzoxazoles 8.35 and 8.36 which are stabilized as their glycosides. The roots of oats contain the triterpene avenacin (8.37) as an allelochemical. Various 

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