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Open AccessArticle

Phytotoxic Responses of Soybean (Glycine max L.) to Botryodiplodin, a Toxin Produced by the Charcoal Rot Disease Fungus, Macrophomina phaseolina

1
Biological Control of Pests Research Unit, US Department of Agriculture-Agricultural Research Service, Stoneville, MS 38776, USA
2
Crop Genetics Research Unit, US Department of Agriculture-Agricultural Research Service, Stoneville, MS 38776, USA
3
Department of Medicinal Chemistry, College of Pharmacy, University of Minnesota, Minneapolis, MN 55455, USA
*
Authors to whom correspondence should be addressed.
Toxins 2020, 12(1), 25; https://doi.org/10.3390/toxins12010025
Received: 13 September 2019 / Revised: 14 December 2019 / Accepted: 18 December 2019 / Published: 1 January 2020
(This article belongs to the Special Issue Mycotoxins in Feed and Food Chain: Present Status and Future Concerns)
Toxins have been proposed to facilitate fungal root infection by creating regions of readily-penetrated necrotic tissue when applied externally to intact roots. Isolates of the charcoal rot disease fungus, Macrophomina phaseolina, from soybean plants in Mississippi produced a phytotoxic toxin, (−)-botryodiplodin, but no detectable phaseolinone, a toxin previously proposed to play a role in the root infection mechanism. This study was undertaken to determine if (−)-botryodiplodin induces toxic responses of the types that could facilitate root infection. (±)-Botryodiplodin prepared by chemical synthesis caused phytotoxic effects identical to those observed with (−)-botryodiplodin preparations from M. phaseolina culture filtrates, consistent with fungus-induced phytotoxicity being due to (−)-botryodiplodin, not phaseolinone or other unknown impurities. Soybean leaf disc cultures of Saline cultivar were more susceptible to (±)-botryodiplodin phytotoxicity than were cultures of two charcoal rot-resistant genotypes, DS97-84-1 and DT97-4290. (±)-Botryodiplodin caused similar phytotoxicity in actively growing duckweed (Lemna pausicostata) plantlet cultures, but at much lower concentrations. In soybean seedlings growing in hydroponic culture, (±)-botryodiplodin added to culture medium inhibited lateral and tap root growth, and caused loss of root caps and normal root tip cellular structure. Thus, botryodiplodin applied externally to undisturbed soybean roots induced phytotoxic responses of types expected to facilitate fungal root infection. View Full-Text
Keywords: botryodiplodin; root infection mechanism; root toxicity; Macrophomina phaseolina; hydroponic culture botryodiplodin; root infection mechanism; root toxicity; Macrophomina phaseolina; hydroponic culture
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Abbas, H.K.; Bellaloui, N.; Butler, A.M.; Nelson, J.L.; Abou-Karam, M.; Shier, W.T. Phytotoxic Responses of Soybean (Glycine max L.) to Botryodiplodin, a Toxin Produced by the Charcoal Rot Disease Fungus, Macrophomina phaseolina. Toxins 2020, 12, 25.

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