BIOFUMIGATION - ISOTHIOCYANATES RELEASED FROM BRASSICA ROOTS INHIBIT GROWTH OF THE TAKE-ALL FUNGUS

The presence of root tissue of the brassicas canola and Indian mustard inhibited growth of pure cultures of the fungal pathogen which causes take-all of wheat [Gaeumannomyces graminis (Sacc.) Arx and Oliver var . tritici, abbreviated as Ggt]. Ggt growth was generally inhibited mor e in the presence of Indian mustard roots than canola roots. Dried irr adiated roots were consistently effective in reducing Ggt growth, but growth inhibition by young live roots and macerated roots was not cons istent. The inhibitory compound(s) were shown to be volatile because t he symmetry of Ggt growth was not affected by the proximity of the Bra ssica tissue. Volatile breakdown products from macerated Brassica root s were identified using a gas chromatograph-mass spectrometer. The maj or compounds found were isothiocyanates (ITCs). Canola roots released mostly methyl ITC and Indian mustard roots released mostly phenylethyl ITC. Low concentrations of these and related compounds inhibited grow th of Ggt in pure culture when supplied as the vapour of pure chemical s in concentrations within the range expected during breakdown of Bras sica roots in soil.