Production of desmethyl-gregatin A, a possible causative toxin of brown stem rot in adzuki bean, by Phialophora gregata f. sp. adzukicola

To elucidate the cause of brown stem rot in the adzuki bean, we re-evaluated the phytotoxins produced in cultures of the causative agent, Phialophora gregata f. sp. adzukicola. The ethyl acetate–soluble acidic fraction of the culture, as well as the neutral fraction, inhibited the growth of alfalfa seedlings. In the neutral fraction, known phytotoxins gregatin A, B, and C or D and penicilliol A were present. Although the phytotoxins in the acidic fraction were unstable, liquid chromatography–mass spectrometry analysis of the partially purified material suggested that one phytotoxin present was the non-methylated gregatin desmethyl-gregatin A (gregatinic acid A).