Physiological Properties Influencing Floret Dynamics Under Stress in a Maize Hybrid and Its Parental Inbred Lines.

Plant dry matter and plant grain yield of genetically identical plants within a plant stand that is uniform in terms of spatial plant distribution and plant emergence may vary in the order of 3 to 5 fold at physiological maturity. The degree of plant-to-plant variability is associated with stress during the life cycle and is greater in older than in newer maize hybrids. A study was carried out to investigate the physiological mechanisms that are associated with the plant-to-plant variability. The frequency distributions of individual plant weights in the maize hybrid CG60×CG102, grown at 16 plants/m², and its two parental inbred lines, grown at 12 plants/m², were monitored during the life cycle using a morphometric methodology. Uniform plants were selected at the 8-leaftip stage.  Besides plant dry matter from the 12-leaftip stage to physiological maturity, rate of leaftip appearance, rate of spikelet initiation, plant and ear growth rate during the silking period, and kernel number and harvest index at physiological maturity were determined. The top 25% of the frequency distribution (by plant weight) was called the dominant plants (D) and the bottom 25% of the frequency distribution was called the dominated plants (d). The D/d ratio was approximately 2 for plant dry matter at maturity for the three genotypes and was about 2 for kernel number of the hybrid and CG60, whereas the ratio was 10 for the inbred line CG102. The association between kernel number and ear growth rate around silking was better than that between kernel number and plant growth rate around silking, indicating that partitioning is important. Dominated (d) plants at the 12 leaftip stage were doing poorly at physiological maturity, but D plants at the 12-leaftip stage did not necessarily do well at physiological maturity.