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

Hamed K Abbas,W Thomas Shier,Nacer Bellaloui,Alemah M Butler,Mohamed Abou-Karam,Justin L Nelson

doi:10.3390/toxins12010025

Hamed K Abbas, W Thomas Shier + Show 4 more

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https://doi.org/10.3390/toxins12010025

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Abstract

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.

Highlights

Charcoal rot is a plant disease caused by the fungus, Macrophomina phaseolina (Tassi) Goid [1], in over 500 commercially-important plant species ranging from ornamental plants to trees to major food and fiber crops, including soybean (Glycine max L. (Merr.))
The objectives of the present study were to investigate the identity of the phytotoxin produced by M. phaseolina isolates from Mississippi soybeans with charcoal rot disease as botryodiplodin, and to characterize some botryodiplodin root toxicity properties that could enable it to play a role in the initial stages of the soybean root infection mechanism of M. phaseolina
(-)-botryodiplodin, but no detectable phaseolinone, was that the toxin preparations contained a small percentage of either phaseolinone or another unknown, but the potent toxin that was responsible for the observed phytotoxicity

Summary

Introduction

Charcoal rot is a plant disease caused by the fungus, Macrophomina phaseolina (Tassi) Goid [1], in over 500 commercially-important plant species ranging from ornamental plants to trees to major food and fiber crops, including soybean (Glycine max L. (Merr.)). Charcoal rot is a plant disease caused by the fungus, Macrophomina phaseolina (Tassi) Goid [1], in over 500 commercially-important plant species ranging from ornamental plants to trees to major food and fiber crops, including soybean An example of the impact of charcoal rot disease on agriculture was provided by attempts to establish commercial natural rubber production with guayule (Parthenium argentatum Gray) in the arid southwest region of the US as an alternative to imported material from the rubber tree (Hevea brasiliensis) [2]. Concerns about (−)-botryodiplodin as a possible contaminant in Roquefort cheese and other foods have led to extensive studies of its possible toxic effects in mammalian systems [10]. Studies on foods and feeds impacted by charcoal rot disease have not been reported

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