Soybean Charcoal Rot Disease Fungus Macrophomina phaseolina in Mississippi Produces the Phytotoxin (−)-Botryodiplodin but No Detectable Phaseolinone

Research on charcoal rot disease in soybeans, and approximately 500 other plant diseases caused by the fungus Macrophomina phaseolina, has been severely hampered by unavailability of phaseolinone (1), an eremophilane sesquiterpenoid phytotoxin proposed to facilitate initial infection. Phytotoxin produced in cultures of disease-causing M. phaseolina isolated in Mississippi, and purified in a manner similar to that reported for 1, was shown to be (−)-botryodiplodin (2), a readily synthesized mycotoxin previously isolated from Botryodiplodia theobromae cultures. Phaseolinone was not detected, suggesting that 2 may be the phytotoxin that facilitates infection. The availability of 2 should facilitate studies on its role in plant disease.