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 deficiency in wheat when applied to crops grown on soils with low availability of these micronutrients. In the present study, the effect of chlorsulfuron 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 previously 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. Chlorsulfuron reduced the shoot dry weight but not root dry weight. Zn concentration and content in shoots and roots were reduced by chlorsulfuron when applied with 0.8 mg Zn kg(-1) soil. Copper concentration was reduced by Chlorsulfuron in roots but not in shoots. Chlorsulfuron reduced 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. Gatcher is the genotype most tolerant to chlorsulfuron among the three wheat genotypes judged by its root system being less affected by chlorsulfuron. Excalibur grew well at the three-leaf stage (growth rate of the third leaf was not significantly inhibited by chlorsulfuron) but not better than Gatcher later because of inhibition of root growth by chlorsulfuron. The results indicate that Zn-efficiency trait of plants may contribute to the tolerance to chlorsulfuron but still there are other mechanisms involved. The reduced content of Zn or Cu may be a consequence of reduced growth of plant roots and alteration of root geometry or morphology because the net uptake rates (based on root surface area) of these micronutrients were not reduced by chlorsulfuron.