Iron and zinc biofortification strategies in dicot plants by intercropping with gramineous species. A review.

The lack of micronutrients such as iron and zinc is a widespread nutrition and health problem in developing countries. Biofortification is the process of enriching the nutrient content of staple crops. Biofortification provides a sustainable solution to iron and zinc deficiency in food around the world. <br/><br/>Reports have highlighted the current strategies for the biofortification of crops, including mineral fertilization, conventional breeding and transgenic approaches. Any approach which could increase root growth and result in a high transfer of Fe and Zn from the soil to the plant is crucial for biofortification. In addition to these approaches, we draw attention to another important aspect of Fe and Zn biofortification: intercropping between dicots and gramineous species.<br/><br/> Intercropping, in which at least two crop species are grown on the same plot of land simultaneously, can improve utilization of resources while significantly enhancing crop productivity, whereas monocropping is a traditional cropping system of only one crop growth. Monocropping has maintained crop productivity through heavy chemical inputs including the application of fertilizers and pesticides. Monocropping has therefore resulted in substantial eutrophication, environmental pollution, a food security crisis and economic burdens on farmers. Monocropping has also reduced the plant and microorganism diversity in the ecosystem. <br/><br/>Compared with monocropped plants, intercropped plants can use nutrients, water and light better due to the spatial and temporal differences in the growth factors and a variety of species-specific mechanisms of physiological response to environmental stress. Intercropping is common in developing countries such as China, India, Southeast Asia, Latin America and Africa. In particular, interspecific interaction facilitates the iron and zinc nutrition of intercropping systems such as peanut/maize, wheat/chickpea and guava/sorghum or maize. Intercropping also increases iron and zinc content in the seeds. <br/><br/>In a peanut/maize case study, the Fe concentrations in peanut shoots and seed were 1.47–2.28 and 1.43 times higher than those of peanut in monocropping, respectively. In intercropping of chickpea and wheat, the Fe contents in wheat and chickpea seed were increased 1.26 and 1.21 times, respectively, and Zn concentration in chickpea seed was 2.82 times higher than that in monocropping. In this review, we focus on exemplary cases of dicot/gramineous species intercropping that result in improved iron and zinc nutrition of the plants. We present the current understanding of the mechanisms of improvement of iron and zinc in intercropping. The available literature shows that a reasonable intercropping system of nutrient-efficient species could prevent or mitigate iron and zinc deficiency of plants. Here, we propose that intercropping can potentially offer an effective and sustainable pathway to iron and zinc biofortification.