Dynamics of Kernel and Embryo Growth of Maize (Zea mays, L.) Crops Exposed to Severe Source Limitations during the Effective Grain Filling Period.

Recently we have demonstrated that kernel oil concentration is determined by the dynamics of both embryo-kernel ratio and embryo oil concentration. Pollen source affects both traits with a higher impact on the former. For a wide range of post-flowering source-sink ratios (i.e. defoliations, pollination timings), a robust relationship between embryo growth rate and kernel growth rate sustained the steady kernel oil concentration. Severe source limitations, however, could reduce the duration of the grain filling period, affecting kernel oil concentration mainly through modifications of embryo-kernel ratio dynamic. In this work, kernels of a normal oil content hybrid (DK752) self-pollinated and those of the same hybrid but pollinated with a high oil content hybrid (5MG), were sampled along the grain filling period to evaluate the effect of periods (ca. 21 days) of severe source limitation (80% reduction of incident solar radiation) on kernel and embryo growth dynamics. Final kernel weight was 50% reduced by early (from 18 to 39 days after silking) source limitations (ESL) due to reductions of the grain filling period (ca. 24%) and of grain filling rate (ca. 21%). When source limitation was late (LSL) imposed (from 39 to 60 days after silking), kernel size was only reduced (ca. 37%) due to a shorter (ca. 18%) grain filling duration. Final embryo weight was also reduced by ESL (ca. 57%) and LSL (ca. 35%) due to a shorter embryo growth period (ca. 27% and 13% for ESL and LSL, respectively) and a lower embryo growth rate (ca. 27% and 13%, for ESL and LSL, respectively). The ESL reduced embryo-kernel ratio of both crosses (ca. 11 and 16.5%, for DK752xDK752 and DK752x5MG, respectively), while LSL only affected (ca. 12.4%) embryo-kernel ratio of DK752x5MG. Consequently, kernel oil concentration was mainly reduced (ca. 20% and 11% for ESL and LSL, respectively) by ESL.