Comparative toxicity of allelochemicals and their enzymatic oxidation products to maize fungal pathogens, emphasizing Fusarium graminearum

Abstract

A series of stable quinones and their precursors, and enzymatic oxidation products of plant allelochemicals were tested for their effect on maize fungal pathogens, primarily Fusarium graminearum. Benzoquinone was typically significantly more toxic than hydroquinone, while 1,2-naphthoquinone was typically significantly more toxic than 1,2-dihydroxynaphthalene. Aspergillus flavus was the most resistant fungus to these compounds, while Phoma medicaginis was the most susceptible. Applying tyrosinase in conjunction with several phenolic compounds only increased the toxicity of gallic acid to Fusarium graminearum. Applying peroxidase generally increased toxicity of all compounds tested to this fungus in a dose-dependent fashion. Ferulic acid was generally the most toxic compound, both alone and when combined with peroxidase and H 2 O 2 , followed by coumaric acid. These results suggest that enzymatic oxidation of plant allelochemicals may result in the generation of products that either are directly toxic to maize pathogens, or indirectly inhibitory due to their ability to tie up nutrients. Nat.

Analysis of the Fusarium graminearum species complex from wheat, barley and maize in South Africa provides evidence of species-specific differences in host preference

“…Because of their inhibitory activity toward some fungi and bacteria, benzoxazinone allelochemicals and related derivatives are thought to be involved in plant disease resistance. Some fungi have been found to have different sensitivity to hydroxamic acids (Dowd et al, 1997;Friebe et al, 1998). It would be of interest to discover whether F. graminearum, F. boothii, and other species within the FGSC are equally sensitive to hydroxamic acids, related benzoxazolinone compounds, or other antimicrobial compounds produced by maize.…”

Association of a Specific Cationic Peroxidase Isozyme with Maize Stress and Disease Resistance Responses, Genetic Identification, and Identification of a cDNA Coding for the Isozyme

“…Because peroxidase activity is substrate dependent as well, increases in disease resistance may be limited by substrate content, as has been shown for insect resistance in tomato expressing high levels of tobacco anionic peroxidase (47). However, because the peroxidase substrate complex is also important in determining the ability of the plant to defend itself against insects and fungi (14,15), studies of the involvement of the pI 9.0 peroxidase are likely to be needed in maize lines of different backgrounds to more fully determine its role in resistance. There is some information to support studying the association of this isozyme and insect resistance, as kernel resistance to insect feeding has been reported for an inbred that produces the isozyme in the pericarp compared to one that does not (10,20).…”

Gallic acid: a versatile antioxidant with promising therapeutic and industrial applications

“…276,277 For instance GA showed antifungal activity against F. fusiformis, Fusarium semitectum and Alternaria altternata. 242 Díaz-Gómez et al 278 demonstrated the antimicrobial effect of GA on Helicobacter pylori, a gram negative bacterium which is one of the leading causes of gastric cancer. It was found to signicantly inhibit the growth of H. pylori.…”