Toxin Production in Soybean (Glycine max L.) Plants with Charcoal Rot Disease and by Macrophomina phaseolina, the Fungus that Causes the Disease.

Hamed K Abbas,Cesare Accinelli,W Thomas Shier,James R Smith,Nacer Bellaloui

doi:10.3390/toxins11110645

Abstract

Charcoal rot disease, caused by the fungus Macrophomina phaseolina, results in major economic losses in soybean production in southern USA. M. phaseolina has been proposed to use the toxin (-)-botryodiplodin in its root infection mechanism to create a necrotic zone in root tissue through which fungal hyphae can readily enter the plant. The majority (51.4%) of M. phaseolina isolates from plants with charcoal rot disease produced a wide range of (-)-botryodiplodin concentrations in a culture medium (0.14–6.11 µg/mL), 37.8% produced traces below the limit of quantification (0.01 µg/mL), and 10.8% produced no detectable (-)-botryodiplodin. Some culture media with traces or no (-)-botryodiplodin were nevertheless strongly phytotoxic in soybean leaf disc cultures, consistent with the production of another unidentified toxin(s). Widely ranging (-)-botryodiplodin levels (traces to 3.14 µg/g) were also observed in the roots, but not in the aerial parts, of soybean plants naturally infected with charcoal rot disease. This is the first report of (-)-botryodiplodin in plant tissues naturally infected with charcoal rot disease. No phaseolinone was detected in M. phaseolina culture media or naturally infected soybean tissues. These results are consistent with (-)-botryodiplodin playing a role in the pathology of some, but not all, M. phaseolina isolates from soybeans with charcoal rot disease in southern USA.

Highlights

The fungus Macrophomina phaseolina (Tassi) Goidanich [1], known by the teleomorph Sclerotium bataticola Taub. [2], is the cause of charcoal rot disease, and other named diseases, in soybeans and aboutToxins 2019, 11, 645; doi:10.3390/toxins11110645 www.mdpi.com/journal/toxins500 other crop and ornamental species in the United States and internationally [3,4,5]
The same cell-free culture filtrates from M. phaseolina isolates were assayed by LC/MS for levels of (-)-botryodiplodin, the toxin previously [35] found associated with culture filtrates of a M. phaseolina isolate from a soybean plant in Mississippi with charcoal rot disease
A wide range of (-)-botryodiplodin levels were observed in both cell-free culture medium filtrates from M. phaseolina isolates from plants with charcoal rot disease and in the roots, but not in the aerial parts, of soybean plants naturally infected with charcoal rot disease

Summary

Introduction

The fungus Macrophomina phaseolina (Tassi) Goidanich [1], known by the teleomorph Sclerotium bataticola Taub. [2], is the cause of charcoal rot disease, and other named diseases, in soybeans and aboutToxins 2019, 11, 645; doi:10.3390/toxins11110645 www.mdpi.com/journal/toxins500 other crop and ornamental species in the United States and internationally [3,4,5]. [2], is the cause of charcoal rot disease, and other named diseases, in soybeans and about. Known as summer wilt, dry weather wilt, or black root disease, results in crop yield loss and seed quality deterioration in soybeans and other crops [6,7,8,9,10,11]. M. phaseolina forms black spore-like mycelial structures called microsclerotia, which allow the fungus to survive over winter. These microsclerotia are the grey and black dots in the stems and roots of soybean plants that give charcoal rot disease its name [16]

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