Basis for Variability in the Cucumber for Tolerance to Chloramben Methyl Ester

Abstract

The physiological basis for tolerance and susceptibility of four lines of cucumber (Cucumis sativusL.) to the methyl ester of 3-amino-2,5-dichlorobenzoic acid (chloramben) was investigated. ‘MSU 3207’ and ‘MSU 0612’ were tolerant (T), whereas ‘MSU 3159’ and ‘MSU 0866’ were susceptible (S). Intraspecific variability was related to higher concentrations of chloramben in the roots of the susceptible lines, resulting from metabolic differences in these lines and rapid absorption of the herbicide by the roots of ‘S-MSU 3159’. Tolerance of ‘T-MSU 3207’ resulted primarily from low uptake and reduced translocation of the herbicide, while tolerance of ‘T-MSU 0612’ was related to, but not necessarily explained by, a peculiar¹⁴C-label distribution pattern in the leaves. Thin-layer chromatographic analysis of methanol-soluble extracts from the lines studied 3 days after¹⁴C-chloramben methyl ester treatment separated six¹⁴C-metabolites in the roots and five in the shoots. After a 4-hr treatment,¹⁴C-chloramben methyl ester was absorbed and translocated more rapidly than¹⁴C-chloramben by all four lines. Tolerance or susceptibility did not always correlate with the total concentration of radioactivity in methanol-soluble shoot and root extracts.