Ascherxanthone B fromAschersonia luteola, a new antifungal compound active against rice blast pathogenMagnaporthe grisea

Abstract

Aims: Fungicide resistance now exists in the rice blast fungus, Magnaporthe grisea, necessitating the need for new active agents. Fungi isolated from habitats in Thailand were screened with reference to this problem. Methods and Results: A new, reliable in vitro screening system based on a microdilution plate format was set up using a virulent strain of M. grisea THL 16. Culture broth extracts from approximately 800 fungal strains were investigated, one of these, Aschersonia luteola BCC 8774, was found to produce an active fungicidal compound, ascherxanthone B, with an IC90 value of 0·58 μg ml−1 (0·95 μmol l−1). An in vivo study of anti‐blast efficacy of ascherxanthone B showed a positive effect in disease reduction. Conclusions: Previous report has shown that a species of Aschersonia produces ascherxanthone A. Research on the species, A. luteola BCC 8774, led to the discovery of related novel metabolite, ascherxanthone B with fungicidal properties. Significance and Impact of the Study: Current methods of rice blast control seem to fail leading to increase in crop losses. Our discovery of the anti‐blast activity shown by ascherxanthone B is the first step in the development of a potentially novel fungicide.

Unusual dimeric tetrahydroxanthone derivatives from Aspergillus lentulus and the determination of their axial chiralities

“…Dimeric tetrahydroxanthones and their derivatives like xanthone−chromanone and chromanone dimers, with attractive antibacterial12, antifungal3 and antimalarial activities4, are a class of structurally interesting natural products produced by multiple fungal and lichenous species5. More than 70 members with 2,2′-, 4,4′- or 2,4′-axial linkages have been isolated and identified since 19585.…”

Chromone derivatives from the wood-decay fungus Rhizina sp. BCC 12292

“…Xanthepinone (4) is reported to inhibit the conidial germination of M. grisea with an MIC of 2 mg/ml (Liermann et al, 2009). The inconsistence with our result may due to the difference of the assay method (Chutrakul et al, 2009). …”

“…Antifungal activity against C. albicans and anticancer activities against KB cells (oral human epidermoid carcinoma), MCF-7 cells (human breast cancer), and NCI-H187 cells (human small-cell lung cancer), were evaluated using the resazurin microplate assay (O'Brien et al, 2000). Antifungal activity against the rice blast pathogen M. grisea TH16 was assayed as previously described (Chutrakul et al, 2009).…”

The Potential of a Fluorescent-Based Approach for Bioassay of Antifungal Agents against Chili Anthracnose Disease in Thailand

“…Preparation of 5,012 crude extracts from these organisms was performed as described previously. 10,11) The extracts were dissolved in 100% DMSO at an initial concentration of 100 mg/mL, 50-mL aliquots were added to the microplate wells, and 28 extracts were tested in triplicate in each plate (Corning, no. 3364).…”

“…The standard antibiotic amphotericin B, previously used as positive control in a rice blast pathogen assay, 10) had an inhibitory effect on the growth of both fungi correlated with fluorescence intensity. The active concentration that caused !80% inhibition of both fungi was 3.13 mg/mL, which is within the accepted 2.0-16.0 mg/mL range by the standard NCCLS method.…”