Phytotoxic Metabolites Produced by Legume-Associated Ascochyta and Its Related Genera in the Dothideomycetes

Abstract

Phytotoxins, secondary metabolites toxic to plants and produced by fungi, are believed to play an important role in disease development by targeting host cellular machineries and/or interfering with host immune responses. The Ascochyta blight diseases on different legume plants are caused by Ascochyta and related taxa, such as Phoma. The causal agents of the Ascochyta blight are often associated with specific legume plants, showing a relatively narrow host range. The legume-associated Ascochyta and Phoma are known to produce a diverse array of polyketide-derived secondary metabolites, many of which exhibited significant phytotoxicity and have been claimed as virulence or pathogenicity factors. In this article, we reviewed the current state of knowledge on the diversity and biological activities of the phytotoxic compounds produced by Ascochyta and Phoma species. Also, we touched on the secondary metabolite biosynthesis gene clusters identified thus far and discussed the role of metabolites in the fungal biology.

Keywords: Ascochyta; Didymella; Phoma; gene cluster; legumes; phytotoxin; secondary metabolites.

Figure 1

Asochitine and anthraquinones produced by the legume-associated Ascochyta and Phoma species. Lentiquinones B and C are epimers.

Figure 2

Macrolides and meroterpenoids produced by the legume-associated Ascochyta and Phoma species.

Figure 3

Solanapyrone congeners produced by Ascochyta rabiei and natural analogs found in other fungal extracts. Sol: Solanapyrone.

Figure 4

Secondary metabolites of hybrid polyketide–nonribosomal peptide origin and simple phenolics produced by Ascochyta lentis, A. lathyri and A. lentis var. lathyri.