Kernel Weight Determination of Extreme Plant Hierarchies in Maize (Zea mays, L.) Crops.

Improvement of maize grain yield has been based on an increased tolerance to crowding stress. At high plant population densities, early interferences among plants within a maize stand determine the onset of individuals with different ability to capture resource (i.e. dominant and dominated plants). These early established plant hierarchies differ in plant growth and biomass allocation to ears, conditioning their reproductive fate (i.e. both kernel number and kernel size). In this work we will study the effect of extreme plant hierarchies on kernel weight and its underlying processes (i.e. potential grain filling rate established around silking; actual grain filling rate and effective grain filling period). We will test the hypotheses of (i) a similar kernel weight between both plant types based on a similar potential grain filling rate, and (ii) a differential kernel weight response to alterations of the post-flowering source-sink ratio (i.e. plant weight gain per kernel). To test mentioned hypotheses a data base (3 field experiments) and a field experiment conducted during 2007/08, will be used to analyze kernel weight dynamic of the extreme plant hierarchies of two hybrids with contrasting tolerance to overcrowding. Data base analysis revealed that dominated plants had a lower kernel size than dominant plants, especially at high plant population densities. Differences in kernel weight between extreme plant types were not related to potential kernel weight established around silking. Contrarily, dominated plants had a lower post-flowering source-sink ratio than dominant individuals. Studies of kernel growth dynamic along the effective grain filling period are necessary to clarify the relationship among post-flowering source-sink ratio, actual grain filling rate and effective grain filling period.