Growth and physiological responses of normal, dwarf, and albino corn ( Zea mays) to clomazone treatments

Abstract

The effects of the bleaching herbicide clomazone (2-[(2-chlorophenyl)methyl]-4,4-dimethyl-3-isoxazolidinone) on the growth of selected mutants of corn ( Zea mays L.) were evaluated. A normal hybrid (“Dekalb XL67”), a gibberellin-deficient dwarf-5 mutant, and a chlorophyll- and carotenoid-deficient albino ( lw 3 ) mutant of corn were exposed to clomazone applied preemergence at rates of 0.0, 0.3, 0.6, and 1.1 kg/ha under greenhouse conditions. Normal corn was very sensitive to clomazone treatments and was severely bleached. Shoot height, shoot dry weight, and chlorophyll content of normal corn were strongly inhibited by all application rates of clomazone. The effects of combined treatments of clomazone and the growth retardant CCC on the growth of normal corn were additive or synergistic. The clomazone induced retardation of the longitudinal growth of normal corn was reversed by exogenously applied gibberellin (GA 3). The dwarf-5 mutant exhibited a greater tolerance to clomazone than normal corn. Clomazone caused a slight chlorosis and reduced the longitudinal growth of this mutant only when applied at the highest rate of 1.1 kg/ha. The short-lived growth of the lethal albino mutant of corn was not affected significantly by clomazone. Normal and dwarf-5 corn responded quite differently when treated with the bleaching herbicide norflurazon. In contrast to the results obtained with clomazone, both normal and dwarf-5 corn were bleached severely by all rates of norflurazon but their shoot heights were not affected by this herbicide. Norflurazon reduced shoot dry weights of normal corn, but not of the dwarf-5 mutant. These results support previously published reports suggesting that clomazone acts by a new mechanism of bleaching action which is different than that of norflurazon. The lesser sensitivity of the gibberellin-deficient dwarf-5 mutant to clomazone and the reversal of clomazone-induced effects on normal corn by exogenous gibberellin suggest a secondary action of this herbicide on gibberellin biosynthesis.