EFFECTS OF HERBICIDE CHLORSULFURON ON GROWTH AND NUTRIENT-UPTAKE PARAMETERS OF WHEAT GENOTYPES DIFFERING IN ZN-EFFICIENCY

Chlorsulfuron has been reported to induce and aggravate Zn and Cu defi ciency in wheat when applied to crops grown on soils with low availabi lity of these micronutrients. In the present study, the effect of chlo rsulfuron on the growth of three wheat genotypes (Triticum aestivum L. , cvs Excalibur and Gatcher, and T. turgidum conv. durum (Desf.) McKay cv Durati) differing in zinc efficiency was examined in Zn-deficient sandy soil fertilised with 0 or 0.8 mg Zn kg(-1) soil. Excalibur has p reviously been identified as the Zn- efficient genotype which can take up more Zn and has higher yield in soils with low plant-available Zn, while catcher and especially Durati are Zn-inefficient genotypes. Chl orsulfuron reduced the shoot dry weight but not root dry weight. Zn co ncentration and content in shoots and roots were reduced by chlorsulfu ron when applied with 0.8 mg Zn kg(-1) soil. Copper concentration was reduced by Chlorsulfuron in roots but not in shoots. Chlorsulfuron red uced the growth rate of the third leaf, decreased the total length of roots (especially the length of fine roots with diameter less than or equal to 0.2 mm), and increased the average root diameter, more so in the Zn-inefficient genotype Durati than in the other two genotypes. Ga tcher is the genotype most tolerant to chlorsulfuron among the three w heat genotypes judged by its root system being less affected by chlors ulfuron. Excalibur grew well at the three-leaf stage (growth rate of t he third leaf was not significantly inhibited by chlorsulfuron) but no t better than Gatcher later because of inhibition of root growth by ch lorsulfuron. The results indicate that Zn-efficiency trait of plants m ay contribute to the tolerance to chlorsulfuron but still there are ot her mechanisms involved. The reduced content of Zn or Cu may be a cons equence of reduced growth of plant roots and alteration of root geomet ry or morphology because the net uptake rates (based on root surface a rea) of these micronutrients were not reduced by chlorsulfuron.