Inhibitory effects of volatile compounds released from rice callus on soybean callus growth: allelopathic evidence observed using in vitro cultures

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When soybean ( Glycine max Merr.) callus was cultured with rice ( Oryza sativa L.) callus in the same culture bottle, an allelopathic evidence of growth inhibition on the former callus was observed. This allelopathic effect was so intense that the growth rates of the soybean callus were reduced by more than 100 fold under may experimental conditions. Further studieds showed that the inhibitory effect was from volatile compounds which were produced by rice callus. In rice cell suspension cultures, the volatile inhibitory compounds were released from rice cells and maintained in the liquid medium rather constantly. These compounds in the supernatant fluid from rice cell cultures were quite heat- and acid-stable, but their activity was reduced considerably by KMnO 4 oxidation. On the contrary, the addition of base to the supernatant fluid greatly enhanced the production of volatile inhibitory material. Limited experiments indicated that the allelopathic effect of inhibition on soybean callus was non-specific with respect to rice cultivars. The intensive inhibitory effect was also observed on callus of other legume species as wella but not on members of the Solanaceae. The species-specific inhibitory effect of allelopathy on cultured cell and callus growth may be useful as a strategy for screening somatic hybrid cells from cultures of fusion-treated protoplasts.