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.

Phytotoxic Secondary Metabolites from Fungi

“…These three chloromonilinic acids were toxic to buffelgrass in a seedling elongation assay, with significantly delayed germination and dramatically reduced radicle growth [40]. Coniochaetone A (16) and rabenchromenone (17) were isolated from the culture filtrates of Fimetariella rabenhorstii, an oak-decline-associated fungus in Iran. They were toxic by causing a necrosis diameter in the range of 0.2-0.7 cm with a leaf puncture assay on tomato and oak leaves [41].…”

“…Some discussed only the biochemical and physiological aspects of phytotoxins [ 12 ], and some others only proposed fungal phytotoxins as potential herbicides [ 11 , 13 ]. Additionally, other reviews only reported on the phytotoxins produced by one fungal genus [ 4 , 14 , 15 , 16 ], or one fungal species [ 17 ]. Some others were reported on the phytotoxins produced by fungi during interactions with one plant species or only one plant group [ 18 ].…”

Reference genome assembly for AustralianAscochyta lentisisolate Al4

“…The secondary metabolite, ascochytine ( Kim et al 2019 ) is produced in the Ascochyta species Ascochyta pisi and Ascochyta fabae and although the biosynthetic gene cluster remains largely intact in A. lentis , premature stop codons in key genes of the cluster preclude the production of the phytotoxic compound in A. lentis . Secondary metabolites from across the Ascochyta and closely related Phoma genera have been studied in detail and evidence suggests that divergence among these species is linked to the taxonomy of divergent secondary metabolite biosynthetic pathways and the resulting metabolites produced ( Kim et al 2016 ; Kim and Chen 2019 ). Secondary metabolite toxins may contribute to the pathogenicity of fungal phytopathogens such as A. lentis , however, none has been found to determine host species or cultivar specificity.…”

Stagonosporopsis pogostemonis: A Novel Ascomycete Fungus Causing Leaf Spot and Stem Blight on Pogostemon cablin (Lamiaceae) in South China

“…Didymellaceae, which belongs to Pleosporales, is one of the largest families in the fungal kingdom [ 26 ]. They include plant pathogens, opportunists, endophytes, and saprobes from a wide range of host [ 27 ].…”