Toxin production in soybean (Glycine max L.) plants with charcoal rot disease and by Macrophomina phaseolina, the fungus that causes the disease

Authors: Abbas, Hamed; Bellaloui, Nacer; ACCINELLI, CESARE - University Of Bologna; Smith, James - Rusty; SHIER, WAYNE - University Of Minnesota

Submitted to: Toxins
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/29/2019
Publication Date: 11/6/2019
Citation: Abbas, H.K., Bellaloui, N., Accinelli, C., Smith, J.R., Shier, W.T. 2019. Toxin production in soybean (Glycine max L.) plants with charcoal rot disease and by Macrophomina phaseolina, the fungus that causes the disease. Toxins. 11(11):645. https://doi.org/10.3390/toxins11110645.
DOI: https://doi.org/10.3390/toxins11110645

Interpretive Summary: Charcoal rot disease is a major disease of soybean, particularly in the Mid-South region, where it has a major economic impact due to the in substantial yield losses it causes. Charcoal rot disease is caused by the mold, Macrophomina phaseolina, which has been the subject of field and laboratory studies to understand the mechanism it uses to infect soybean plant roots from the soil. These studies have established a role for the toxin botryodiplodin and other mycotoxins in the root infection process. These results could help provide information about the infection process that could identify the signal(s) the soybean plant releases and the fungus detects that let it know that a root target is available in the soil. Breeders may be able to discover soybean varieties that do not release the signal for toxin release by the fungus, thereby preventing infection and giving the soybean variety resistance to charcoal rot disease. The results from this study will provide useful information to the public and private sector research units including ARS, academia, and industrial grain producers.

Technical Abstract: Charcoal rot disease, caused by the fungus Macrophomina (M.) 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 culture medium (0.14-6.11 µg/mL); 37.8% produced traces below the LOQ limit (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 production of other unidentified toxin(s). Widely ranging (-)-botryodiplodin levels (traces to 3.14 µg/g) were also observed in roots, but not aerial parts, of soybean plants naturally infected with charcoal rot disease. This is the first report of (-)-botryodiplodin in tissues of plants with charcoal rot disease. No phaseolinone production 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.