MORPHOLOGICAL AND PHYSIOLOGICAL DIFFERENCES IN THE RESPONSE OF CEREALS TO ZINC-DEFICIENCY (REPRINTED FROM WHEAT - PROSPECTS FOR GLOBAL IMPROVEMENT, 1998)

Greenhouse and growth chamber experiments were carried out using seven bread wheat (Triticum aestivum), three durum wheat (ir: durum), two r ye (Secale cereale), three barley (Hordeum vulgare), two triticale (x Triticosecale Wittmack) and one oat (Avena sativa) cultivars to study response to zinc (Zn) deficiency and Zn fertilisation in nutrient solu tion and in a severely Zn deficient calcareous soil. Visual Zn deficie ncy symptoms, such as whitish-brown necrotic patches on leaf blades, d eveloped rapidly and severely in the durum wheat and oat cultivars. Br ead wheat showed great genotypic differences in sensitivity to Zn defi ciency. In triticale and rye, visual deficiency symptoms were either a bsent or appeared only slightly, while barley showed a moderate sensit ivity. When grown in soil, average decreases in shoot dry matter produ ction due to Zn deficiency were 15% for rye, 25% for triticale, 34% fo r barley, 42% for bread wheat, 63% for oat and 65% for durum wheat. Di fferential Zn efficiency among and within cereal species was better re lated to the total amount of Zn per shoot, but not to the Zn concentra tion in the shoot dry matter. However, in leaves of Zn efficient rye a nd bread wheat cultivars, the activity of Zn-containing superoxide dis mutase was greater than in Zn inefficient bread and durum wheat cultiv ars, suggesting higher amounts of physiologically active Zn in leaf ti ssue of efficient genotypes. When grown in nutrient solution, there wa s a poor relationship between Zn efficiency and release rate of Zn-che lating phytosiderophores from roots, but uptake of labelled Zn (Zn-65) and its translocation to the shoot was higher in the Zn efficient rye and bread wheat cultivars than in inefficient bread and durum wheat c ultivars. The results demonstrate that susceptibility of cereals to Zn deficiency decline in the order durum wheat > oat > bread wheat > bar ley > triticale > rye. The results also show that expression of high Z n efficiency in cereals was causally related to enhanced capability of genotypes to take up Zn from soils and use it efficiently in tissues.