Maize kernel composition and post-flowering source-sink ratio

In maize (Zea mays L.), there is little information on how the availability of assimilates during the effective grain-filling period affect final kernel quality. The objective of our research was to analyze the response of kernel starch, protein, and oil to changes in the post-flowering source-sink ratio (i.e., post-flowering shoot biomass increase per kernel). Two commercial hybrids of different kernel weight (KW) and protein content were grown at two stand densities (3 and 9 plants m(-2)) during 1998-1999 and 1999-2000. Pollination treatments were used to modify kernel number per plant (KNP). As KNP increased, starch, protein and oil yield per plant increased, but yield per kernel decreased (P < 0.05) in all treatment combinations. In both genotypes, starch, protein, and oil content per kernel varied between 114 to 238, 15 to 48, and 7 to 17 mg kernel 1, respectively, and concentrations varied between 650 to 700, 80 to 140, and 40 to 60 g kg(-1) dry weight, respectively. Within each hybrid, the post-flowering source-sink ratio explained (P < 0.01) the response of each kernel component content to modifications in KNP and stand density. In both genotypes, kernel starch, protein, and oil content were all maximized at the same post-flowering source-sink ratio (similar to420 and 570 mg kernel(-1) in DK664 and DK752, respectively). A decrease in the source-sink ratio beyond a specific threshold promoted a decrease in the relative protein content and an increase in the relative starch content. Limitations other than assimilates seem to govern the relative oil content of kernels, as no relation with the post-flowering source-sink ratio was found.