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Phytotoxic Ophiobolins Produced By Helminthosporium Gramineum Rabenh, A Potential Bioherbicide For Control Of Barnyardgrass (Echinochola Crus-Galli)

Qinsheng Yuan, Liuqing Yu, Guifang Duan, Yongjun Zhou

3-Anhydroophiobolin B, ophiobolin A, 3-anhydro-6-epiophiobolin A and 3-anhydro-6-epiophiobolin B were isolated from mycelia and culture filtrate of helminthosporium gramineum rabenh, a fungus phytopathogenic to barnyardgrass (Echinochloa crus-galli). Their structures were identified by detailed analysis of the NMR spectral data and by comparison with reported data. Root growth inhibition bioassays showed that all four ophiobolins inhibited root growth of barnyardgrass and rice at high concentration (500μg ml-1) but only ophiobolin A inhibited rice root growth at low concentration. Root growth of barnyardgrass was much more susceptible to ophiobolin A than was rice. Ophiobolin A was phytotoxic to some but not all of the plant species tested by leaf bioassay in vivo. However, 3-anhydroophiobolin B, 3-anhydro-6-epiophiobolin A, and 3- anhydro-6-epiophiobolin B exhibited no phytotoxicity to any of the test species in vivo. Clarification of the structure–activity relationships among these ophiobolin analogs may provide useful chemical information.