Relative grain zinc loading ability of cereals (rice, wheat, maize) and a grain legume (chickpea)

Abstract

Data from field experiments conducted at the ICAR-Indian Agricultural Research Institute, New Delhi, India during the last few years on Zn biofortification of the cereals, viz. wheat (Triticum asestivum L.), rice (Oryza sativa L.) and maize (Zea mays L.) and a grain legume (chickpea) were utilized in studying the comparative efficiency of these crops in grain Zn loading. Although Zn uptake per tonne of grain produced was the highest, the grain Zn loading was the lowest in rice. Zn concentration in grain (an intensity factor) was the highest in wheat at 46.8 mg/kg, closely followed by maize at 45.1 mg/kg, chickpea at 41.8 mg/kg and was the least for rice kernels at 21.2 mg/kg. ZnHI (a capacity factor for measuring grain Zn loading) was also the highest for wheat at 51%, followed by chickpea at 39.3%, maize at 35.9% and was the least for rice at 17.9%. Further, rice grain contains husk (about one-third by weight) and only kernel is consumed, for which ZnHI was only 6.3%; a major part of Zn loaded on grain in rice goes to the husk. Thus, from the Zn nutrition point of view rice is the poorest cereal. However, rice deserves utmost attention, because it is the staple food in South, Southeast and East Asia, where about 62.5% of the world’s people live and hunger and malnutrition is rampant. Since most grain Zn loading in rice is from the Zn absorbed by the roots through xylem in contrast to other crops, where it is mostly achieved through mobilization of Zn in the vegetative tissue through phloem, it is suggested that rice plant types using grain Zn loading through phloem be developed. It is necessary, because applied Zn gets fixed or precipitated in soil through several mechanisms and its availability to rice plants gets reduced as it reaches grain filling stage.