Black root rot development in cotton roots caused by Thielaviopsis basicola and the possible rôle of methyl acetate in pathogenesis

Abstract

Fusel oil components produced in vitro by Thielaviopsis basicola were: methyl acetate, ethyl acetate, ethyl alcohol, propyl acetate, propyl alcohol, isobutyl alcohol, isoamyl acetate and isoamyl alcohol. With the exception of methyl acetate and propyl alcohol all fusel oil components produced by T. basicola have been reported previously. Methyl acetate was identified by gas-liquid chromatography and by gas-liquid chromatography-mass-spectrometry in fungal and cotton root extracts. In diseased cotton roots methyl acetate was found in amounts that were 10 times greater than in healthy roots. Studies on the phytotoxicity of methyl acetate to cotton roots showed that a concentration of methyl acetate as low as 0·126 m m caused browning of tissues and other symptoms typical of black root rot. When a possible relationship was tested between the in vitro production of methyl acetate and isoamylalcohol by T. basicola and virulence of T. basicola in cotton, no apparent association was found. Mutant isolates of T. basicola, which produced either more or less of methyl acetate and/or isoamyl alcohol than their highly virulent parent did not differ from their parent in the severity of black root rot they caused in cotton roots. Associated with the development of black root rot was a marked increase in peroxidase activity. The phytotoxicity of methyl acetate and its tenfold increase in concentration in diseased roots compared with healthy roots suggest a possible rôle of methyl acetate in pathogenesis.