Mellein: Production in culture by macrophomina phaseolina isolates from soybean plants exhibiting symptoms of charcoal rot and its role in pathology

Authors: KHAMBHATI, VIVEK - U.S. DEPARTMENT OF AGRICULTURE (USDA); Abbas, Hamed; SULYOK, MICHAEL - UNIVERSITY OF NATURAL RESOURCES AND LIFE SCIENCES, VIENNA; TOMASO-PETERSON, MARIAMORENA - MISSISSIPPI STATE UNIVERSITY; Chen, Jian; SHIER, WAYNE - UNIVERSITY OF MINNESOTA

Submitted to: Frontiers in Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/16/2023
Publication Date: 2/8/2023
Citation: Khambhati, V.H., Abbas, H.K., Sulyok, M., Tomaso-Peterson, M., Chen, J., Shier, W.T. 2023. Mellein: Production in culture by macrophomina phaseolina isolates from soybean plants exhibiting symptoms of charcoal rot and its role in pathology. Frontiers in Plant Science. 14-2023. https://doi.org/10.3389/fpls.2023.1105590.
DOI: https://doi.org/10.3389/fpls.2023.1105590

Interpretive Summary: Mellein is one of the many toxins produced by the fungus Macrophomina phaseolina which causes charcoal rot of soybean and numerous other plant diseases. Many fungal toxins have been determined to play an important role in the infection of plants, so this experiment was designed to determine if mellein causes the symptoms of charcoal rot. Results showed that mellein can cause wilting in the soybean host but only at extremely high concentrations that do not exist in nature. These results suggest that more research is needed to determine whether one of the many other toxins produced by this fungus is responsible for the disease symptoms in soybean.

Technical Abstract: Macrophomina phaseolina (Mp) is a fungal pathogen proposed to enter host roots by releasing toxins that induce local necrosis in roots allowing entry of hyphae. Mp is reported to produce several potent phytotoxins, including (-)-botryodiplodin and phaseolinone, but isolates that do not produce these phytotoxins retain virulence. One hypothesis explaining these observations is that Mp isolates may possess sufficient genetic variability to allow production of other unidentified phytotoxin(s) responsible for virulence. A previous study of Mp isolates from soybean found 14 previously unreported secondary metabolites, including mellein, which has various biological activities. This study was conducted to investigate the frequency and amounts of mellein produced in culture by Mp isolates from soybean plants exhibiting symptoms of charcoal rot and to investigate the role of mellein in any observed phytotoxicity. LC-MS/MS analysis of cell-free culture filtrates (CCFs) from 89 Mp isolates revealed that 28.1% produced mellein (49–2,200 µg/L). In soybean seedlings in hydroponic culture, Mp CCFs diluted to 25% (vol/vol) in hydroponic growth medium induced phytotoxic symptoms with frequencies of 73% chlorosis, 78% necrosis, 7% wilting, and 16% death, and at 50% (vol/vol) induced phytotoxicity with frequencies of 61% chlorosis, 82% necrosis, 9% wilting, and 26% death. Purified mellein (40–100 µg/mL) in hydroponic culture medium induced wilting. However, mellein concentrations in CCFs exhibited only weak, negative, insignificant correlations with phytotoxicity measures in soybean seedlings, suggesting that mellein does not contribute substantially to observed phytotoxic effects. Further investigation is needed to determine if mellein plays any role in root infection.