Abstract
Grain yield and mineral nutrient concentration in cereal crops are usually inversely correlated, undermining biofortification efforts. Here, sink size, expressed as kernel number per cob, was manipulated by controlling the time when the silks of sweetcorn (Zea mays) cv. Hybrix 5 and var. HiZeax 103146 were exposed to pollen. Twelve other varieties were manually pollinated to achieve the maximum potential kernel number per cob, and kernel Zn concentration was correlated with kernel number and kernel mass. As kernel number increased, kernel Zn concentration decreased, with the decrease occurring to similar extents in the embryo tissue and the rest of the kernel. However, total kernel Zn accumulated per cob increased with increasing kernel number, as the small decreases in individual kernel Zn concentration were more than offset by increases in kernel number. When both kernel number and mass were considered, 90% of the variation in kernel Zn concentration was accounted for. Differential distribution of assimilates and Zn to sweetcorn cobs led to significant decreases in kernel Zn concentration with increasing kernel number. This suggests there will be challenges to achieving high kernel Zn concentrations in modern high-yielding sweetcorn varieties unless genotypes with higher Zn translocation rates into kernels can be identified.
Highlights
Micronutrient deficiency is a severe nutritional problem affecting approximately 30% of the world’s population, mainly in developing countries (Kennedy et al, 2003)
The 14 sweetcorn varieties were manually self-pollinated to achieve the maximum potential kernel number.These varieties were harvested at 21 days after pollination (DAP), Kernel Zn concentration is influenced by kernel number | 4987 five cobs were sampled, and the kernel number per cob was determined
Hybrix 5 with varying kernel numbers at different maturity stages (18–28 DAP) is shown in Fig. 1 and Table 1.The rate of accumulation of both Zn and dry matter was greatest at 21–24 DAP and was either maintained or declined to different extents at 24–28 DAP (Table 1)
Summary
Micronutrient deficiency is a severe nutritional problem affecting approximately 30% of the world’s population, mainly in developing countries (Kennedy et al, 2003). One approach to addressing this issue of malnutrition has been through agronomic and genetic biofortification that aims to increase the concentration of a target micronutrient in the edible fraction of staple crops. Examples of species in which intensive biofortification efforts have been made include rice (Oryza sativa), wheat (Triticum aestivum), and maize (Zea mays). (White and Broadley, 2009) Despite these efforts, achieving the combination of high yield and high micronutrient concentration has proved challenging, as crop yield is usually inversely correlated to mineral nutrient concentration (Davis et al, 2004; Murphy et al, 2008). Decreases in the N, protein, and oil concentrations of shoots and kernels have been observed with increasing maize shoot biomass and kernel yield (Scott et al, 2006; Riedell, 2010; Abdala et al, 2018).
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